Chapter ten

The sand-over-gravel approach, typically for bowling greens and golf greens

10.1
Introduction

Where there is a need for rapid drainage, approaching 25 mm (1 in) per hour, and a true, uniform, fine-turf surface over which a ball will roll easily and predictably, this can be achieved only by a well-maintained sand soil, rafted over a drained gravel bed. Such a sand soil is unlikely to exceed 400 mm (16 in) in depth and will provide only a maximum of 14 days water supply to meet peak demand in summer. With this type of construction, therefore, it is essential to make provision for efficient irrigation.

Cheaper alternatives are described in section 11.2. It is appropriate only where a sloped or undulating surface is an acceptable feature of the game and combines limited infiltration and discharge to underdrains with efficient shedding of surface water to peripheral soakaways or ditches. The overall rate of discharge through the soil is unlikely to be more than a tenth of that of a gravel rafted construction, the rest being cleared, like storm water, over the surface. However, it is less dependent than a rafted construction on special provision for irrigation as the grass can root through any shallow carpet of sand to make use of the water stored in the underlying soil.

10.2
Sand-over-gravel approach for fine turf

A sand soil, rafted over a drained gravel bed, has special problems of its own as well as problems it shares with any other constructions in which the rooting medium is made up predominantly of sand.

10.2.1
General principles

Depth of sand soil

One effect of the layered nature of this construction is that the finer pore system of the sand will accumulate infiltered water to the full depth of its critical tension before shunting excess through to the air-filled pores of the gravel drainage bed. The gravel layer acts like an air lock, creating a perched watertable in the sand above. To obtain maximum benefit for

FIGURE 10.1 Moisture profiles in sand soils, on level sites, rafted over gravel. (a) Deeper rooted, less matted turf. (b) Shallow, root-matted, turf. Initially, water applied to the surface of either soil will tend to accumulate to critical tension depth within the range of pore sizes present in the combined topsoil and blinding layers. Only as this layer is filled, to the extent that air entrapment and pore size allows, will excess then be shunted through the large-pore system of the gravel bed and onwards to underdrains. So long as the gravel bed remains sufficiently air-locked to form a capillary break at the sand/gravel interface, water within the critical tension zone of the sand layer will be retained after drainage from the gravel bed has ceased.

Where provision is to be made for sub-irrigation up through the gravel bed, there are advantages to be had from making provision for controlled air-venting from the top of the gravel.

water storage the sand soil should be built up to a height close to three-quarters of its critical tension (to predict, see Chapter 7, page 118). Under these circumstances the construction will combine the benefits of an even moisture profile with maximum water storage capacity and efficient clearance of excess (Figure 10.1). Too shallow a depth, i.e. half the critical tension of the sand used to form the topsoil or less, will encourage the persistence of surface wetness after rain, especially in winter, and will not increase the reserve of stored water with which to avoid the ill-effects of desiccation during drought. Though this tendency for surface wetness to persist will assist sward establishment, by encouraging rapid and uniform seed germination, it will do likewise for weeds and moss. Too great a depth of soil over the gravel bed, i.e. a depth greater than the critical tension of the sand used to form the topsoil, will not increase the water storage capacity but merely place the stored water reserve further beneath the surface. The surface will then tend to dry off rapidly, becoming loose and difficult for the establishment of new grass from seed.

As no natural sand is likely to be formed of particles all exactly the same in size and shape, heterogeneous packing will ensure at least a twofold range in pore size and a diffuse upper boundary to the water storage zone (see Figure 4.3c where the situation in columns of two different sands is quantitatively described). Soil depth to gravel surface, therefore, is bound to be a compromise, though the critical tension of the sand that dominates the topsoil will be the main consideration. Other factors will include the need to allow for long-term settlement, the need on some surfaces to incorporate slopes, and the need to allow for the balance likely to be struck between removals and additions in the course of maintenance.

Providing for slope

To construct the sloping surfaces required for golf greens and crown bowls there would appear to be two variations possible in the sand soil over gravel approach:

1.keep the surface of the gravel bed horizontal and vary both the depth and the character of the overlying soil;

2.incorporate the required undulations in the construction of the gravel bed and then make the overlying soil uniform in character and uniform in depth.

The first option requires the high spots to be created, either by an additional layer of finer textured sand, or by more of the initial fine sand suitably ameliorated with soil. In either case the effect will be to raise the level of the stored-water zone, coincident with the elevation of the surface.

The second option will require insertion of vertical barriers of polythene sheet around contours, e.g. at 100 mm (4 in) height intervals, to isolate the zones with potential for water storage in the elevated areas. Without such barriers water retained in the pore space would tend to be dragged away, downslope, leaving the high spots dry.

However, neither approach is likely to be entirely successful without further adjustments during maintenance: for example, local modification of the texture of the surface by careful choice of topdressing, especially when this can be incorporated after hollow-tine spiking.

Type of sand

As no element of bounce is favoured either in golf or bowls, the sand forming the mineral skeleton of the topsoil should be spherical and of uniform particle size so as to be yielding enough to deaden bounce on impact.

The grade of sand chosen to form the topsoil should fall well within the topsoil sand category in the Stewart zone system. If the D _K value (Chapter 7,page 118) is close to 0.170 mm, as might be the case for a fine topsoil sand, or 0.220 mm, as might be the case for a medium topsoil sand, then the surface should be built up to 350 mm (14 in) or 270 mm (l01/2 in) respectively. But note, within these overall construction depths the 100 mm (4 in) of blinding sand is likely to be included (Chapter 7,page 120). To allow for long-term settlement the initial depths might be increased by a further 10–20%, according as the initial soil is organic rich and/or unconsolidated.

Despite the old prejudice against using even slightly calcareous sands on fine turf, many fine greens have been created and subsequently topdressed with local dune sand of this type; those at Portrush in Northern Ireland and Newquay in Cornwall, being very good examples. The prejudice against calcareous sands has merit in so far as lime encourages earthworms, but a sudden change in pH upwards may also allow Ophiobolus patch disease to flourish temporarily. This disease seems to behave like an opportunist, flourishing temporarily in an immature soil, or when a sudden change in the chemistry of the soil environment upsets the existing microbial community and presents it with an opportunity to flourish. If it does manage to invade then it may give trouble for a few years before being subdued again by the longer-term, competitive efficiency of other micro-organisms.

There is much to be said for aiming at consistency in the sand used for construction and subsequent topdressing. This will avoid both the adverse effects of soil layering and also any risk of upsetting an established, healthy equilibrium in the biology of the soil. The aim should be to select, at time of construction, sands that are not only cheap and meet the necessary physical requirements but also afford the prospect of long-term availability; keeping in mind the years of topdressing that lie beyond the initial task of construction.

Consolidation during construction

To limit the risk of subsequent settlement upsetting the desired final levels, it is important to take care over the initial consolidation of the construction layers. This can best be achieved by wetting up from below (section 10.4), but where the necessary facilities for sub-irrigation are not available, settlement may well continue into the first year following construction. Saturated or completely dry sand settles well but moist sand is very sticky and needs a great deal of heeling and prodding to ease the sand particles into a stable, close-packed arrangement. Until this is achieved any surface application of water may lead to the soggy feel of a surface buoyed up by trapped air. It is for this reason that each 100–150 mm (4–6 in) layer of sand should be well consolidated before another layer is built on above.

Problems at the perimeter

If, around the periphery, the sand of the green abuts a vertical face of fine-textured soil there will be a tendency for the finer pores in the soil to abstract water from the coarser pores in the sand. To protect against any consequent risk of localized desiccation, consideration should be given to inserting a vertical plastic barrier between the soil and the sand. This need only extend from just below the surface to the full depth of the sand/soil junction (W in Figure 10.2), but if it extends to the whole depth of the excavation, it will also protect the gravel bed from the lateral incursion of soil.

Ameliorating the sand

Any soil or organic supplements should not be added in quantities likely to take over physical control of the medium, i.e. no more than 15% silt plus clay, or 10% organic matter, both estimated as percentage dry weight. Horticultural lignite can provide a durable, particulate, organic source which, unlike coal, its harder more fully carbonized relative, is not biologically inert and seems to release enough nitrogen and phosphate to encourage root branching in its vicinity. Seaweed meal, and other properly prepared organic residues, can provide a lush, biologically controlled, wide spectrum, slow release source of nutrients, valuable in a sandy medium which is not well endowed with mechanisms for soluble nutrient retention. A good topsoil might appear to be a cheaper alternative but it will be of value only so long as it retains its water-stable, granular structure. In the longer term the granular structure will collapse as the organic binding agents are dissipated by microbial decay and there are no earthworms to achieve the necessary restructuring. As a result the fine-particle components will then be free to migrate and may then block the free-draining pore space.

Grassing up

Choosing between direct seeding and turfing

For instant, visual effect, e.g. to discourage vandalism, turfing has much to commend it, but in the time taken to achieve a top quality playing surface, there is unlikely to be much difference between starting from direct seeding on site and starting from bought-in turf, provided conditions are ideal for establishment either way. The problem with seed is to get rapid, uniform germination, especially on a very sandy soil where there is always the added hazard of windblow, should the surface be allowed to dry out. Use of pre-germinated seed may shorten the period of anxiety but, having germinated, the seedling must not be left to desiccate. Part of the problem with turf is that not only must the species be appropriate but so must the soil that comes with it. A loam or organic-rich medium may be excellent for turf production but as a cap over the surface it may

FIGURE 10.2 Construction diagrams for putting and bowling greens: (a) bowls; (b) golf.

not benefit the performance of the soil already in situ. This is particularly important where the soil on site is necessarily very sandy to assist with drainage or, as for cricket (section 12.2), of a clay content appropriate for the development of pace.

The cost differential between direct seeding and turfing is considerable. Sward establishment from top quality turf can easily be ten times as expensive as direct establishment from seed, but this must be viewed as one part only of an overall construction budget. Loss of income from green fees because of delays in sward establishment will not help meet the interest payments on a loan. With turf, play may begin as soon as the sward has been stabilized in place by root anchorage, whether or not the playing characteristics are ideal. The only proviso is that the remedial action necessary to deal with any shortcomings in the playing surface can be carried out by the greenkeeping staff without undue interference with play: for example, core extraction followed by solid-tine spiking to lower high spots caused by uneven settlement, or hollow tine coring followed by sand topdressing to progressively remove an inappropriate capping of turf soil before it becomes buried, to persist as a drainage barrier under repeated increments of sand topdressing. There are no short cuts to sward use after establishment from seed but, since the character of the soil should be ideal, the initial maintenance can be concentrated solely on grooming the grass ready for play.

If the club can be persuaded that fine turf used for sport will require some provision for irrigation then it would be as well to install this at time of construction so as to have it available during the grassing-up period. It will be invaluable when seeding, not only to help initiate uniform and rapid germination and sustain subsequent growth, it will also be there to stabilize the surface against windblow in the event of drought. With turf, it will be there to wet up the soil surface before placement of the turves, encouraging root extension into the underlying soil. It will be there also to keep the turves moist until anchored against shrinkage. (Bounce variation arising from the shrinkage of new turves on a cricket square is discussed in Chapter 12, page 186.)

Turfing is an expensive option. Where economies are being sought, as with a DIY project, and seeding can be timed to take full advantage of warm, moist conditions, then seeding is a cheaper alternative. In Britain, after seeding in late August or early September a good sward can be established before winter and brought into use after thickening up in the following spring. (Further advice on seeding and working up a sward for use is given in section 10.3 and 10.5.)

Choice of species

The grass species chosen must be predominantly vertical in growth habit above ground, yet tolerant of frequent, close mowing. This could be achieved by a strongly rhizomatous, single grass species but, in Britain, is most commonly sought by seeding up with a mixture of suitable varieties of agrostis and fescue.

Recognizing and dealing with the problem of seed size

One problem with a fescue/agrostis mixture is that a single seed of fescue is some ten times larger than a single seed of agrostis so that such a mixture will readily segregate with agitation to leave the large fescue seed at the top and the fine agrostis at the bottom. This can happen in a seed hopper making it difficult to sow a mixture evenly. If possible, negotiate for the two species to be supplied separately, sowing them evenly in separate passes, crossing at right angles (page 159).

10.2.2
Management

Some practical aspects of management are also discussed in Appendix F.

Earthworms

Earthworms must be eliminated from bowling and golf greens as surface casts interfere with play. Therefore, if the soil is to drain rapidly it must consist primarily of sand. Also, without earthworms, there will be no natural agent present to incorporate organic residues off the surface. This means that organic debris will have to be removed physically or cliented and buried by regular topdressing, primarily with sand (Appendix F).

Topdressing

Frequent mowing, plus the surface accumulation of organic matter and fertilizer phosphate, will encourage surface rooting. If ignored this will in time make the sward sensitive to drought and intolerant of wear. The essential counter-measures will include scarification, hollow-tine spiking and again, regular application of very sandy topdressings.

Pest control

Any neglect of maintenance that leads to the surface development of a stable, root-bound mat of amorphous organic matter, or a loose accumulation of fibrous thatch, will favour the spread of the thread-like hyphae of fungal diseases and the root-eating larvae of insect pests.

10.3
Outline specifications for gravel-rafted golf and bowling greens

1.Excavate to form a foundation surface 125 mm deeper than the critical tension of the topsoil sand. For example, 125 mm+350 mm=475 mm (19 in) for a fairly fine topsoil sand intermediate between SN14 and SN15 in Table 7.1, or 125 mm+225 mm=350 mm (14 in) for a medium topsoil sand like SN12.

2.Blind the excavated, soil surface with a synthetic fabric filter, or excavate 30–40 mm deeper and use blinding sand in place of a fabric filter. The aim is to prevent the movement of soil up into the base of the gravel bed.

3.(a) For a bowling green, install a pipe drain of not less than 75 mm (3 in) in diameter in a shallow trench, 150 mm (6 in) wide and 150 mm (6 in) deep, located beneath the perimeter ditch. This should be organized to intercept all water flowing off the surface of the green and out of the gravel drainage bed, Figure 10.2. The pipe should fall at a steady gradient of not less than 1:200, proceeding both ways round the periphery to an outfall pipe at the opposite diagonal. Backfill the trench with trench gravel, tucking the edge of the synthetic filter fabric (if used) down the inner wall of the trench and anchoring with the gravel backfill.

(b)For a golf green, install one or more 150 mm (3 in minimum) pipe laterals in 150 mm (6 in) wide, 150 mm (6 in) deep trenches, linked through to a pipe main for discharge. This system of under-drains should be organized to intercept water according as it will flow through the gravel bed and discharge to a suitable outfall. If a synthetic filter fabric is to be used io blind the excavated soil surface, slit the fabric along the line of the drain trenches and tuck the spare fabric down, against the side walls, then put the pipes in place and backfill the trenches to the top with trench gravel. Again, a 10 mm layer of blinding sand can be used to blind the surface of the exposed soil in place of a fabric filter, Figure 10.2. Place plastic sheeting vertically around the side walls to prevent the surrounding soil from withdrawing stored water from the sand soil of the green.

4.Spread a 125 mm (5 in) deep carpet of a fine trench gravel, preferably somewhat angular to aid stability, following with 100 mm (4 in) of a fine blinding sand. Firm each layer into place by treading, heeling, raking and making good to appropriate levels. For both materials assume a requirement of 160 kilograms per square metre of surface for a layer intended to be 100 mm deep after consolidation.

5. Spread the topsoil, consisting of topsoil sand plus supplements, to a firmed, uniform, consolidated depth of 250 mm (10 in) or 125 mm (5 in), according as the sand is the fine or the medium topsoil grade. Supplement below 100 mm (4 in) with 2% by weight of horticultural lignite. The top 100 mm (4 in) should contain the full range of supplements listed below under (a). For an approximate estimate of the materials required assume 150 kg of dry topsoil sand per square metre of surface, for a layer intended to be 100 mm deep after supplementation and initial consolidation. Adjust for actual depth and area, then use this total to estimate the weight of each supplement required. When ordering the sand, however, add 5% to allow for wastage. Any excess should be stored under cover and used subsequently for topdressing.

Use one of two methods to mix supplements into the topsoil sand:

(a)Pre-mix batches of sand with supplements off site, using the following weights of supplement per 150 kg dry weight (1 m²) of topsoil sand:

3–4.5 kg low-fibre compost (i.e. C:N ratio less than 30) such as seaweed meal, worm compost, pelleted poultry manure, or composted farm yard manure 4.5 kg horticultural lignite 0.75 kg semi-organic, slow release or pre-seeding type of fertilizer, eg. 7%N: 10% P₂0₅: 7%K₂O.

Firm into place by repeated sequences of treading, heeling and raking to re-level, then roll in at least two directions. Throughout the firming process, try to keep the topsoil mixture slightly moist and as little agitated as possible so as not to allow the lighter components of the mix to segregate and rise to the surface. Check that the consolidated depth allows for further long-term settlement, assuming an organic-rich sandy layer may eventually settle a further 1/4th of its depth, and sand alone, 1/10th. Make up with additional material, if necessary, and again firm into place before checking levels.

(b)Spread sufficient topsoil sand to raise the surface to a level 100 mm (4 in) short of the final height, and consolidate. Then, spread uniformly over this sand surface the total amount of supplements required to ameliorate the final increment of topsoil sand. If need be, dilute supplements with two to three times their volume of topsoil sand to make it easier to achieve a uniform distribution. Then cover with the amount of topsoil sand calculated to achieve the required final height after consolidation. Use a spring-tine harrow, or equivalent subsoiling tine system, to reach through to the buried layer of supplements. Proceeding slowly and with caution, work the supplements up through the sand. Aim at an even mixture, getting under the supplement layer so as to avoid leaving any concentration at depth. Again, do not agitate excessively, e.g. by rotary cultivation, or light materials will tend to accumulate at the surface. Finally, tread, heel, rake and make good to consolidated design level as described in (a) above.

When a stone-free, sterilized topsoil is available with a water-stable, granular structure, and known particle-size composition, this may be used to form the whole topsoil if suitably ameliorated with topsoil sand (Appendix 3). The seaweed and fertilizer supplementation will still be required for the top 100 mm but the lignite can be left out entirely. The sand content of the soil can be used to cut down on the requirement for topsoil sand. For example, if the soil is 25, 50, 75 or 100% silt plus clay this can be mixec in 1:1, 1:3, 1:5, or 1:7 dry-weight, soil:sand ratios, to form a free-draining, loamy-sanc medium no more than 121/2% silt plus clay, reducing the requirement for topsoil sand by one half, one quarter, one sixth or one eighth.

6. After the trued and consolidated surface has been thoroughly wetted to a depth of 100 mm (4 in) by rain or overhead irrigation, and when weather conditions look favourable for seed germination, topdress with a low-nitrogen, pre-seeding fertilizer, at about 70 g/m² (2 oz/sq yd). Seed with a fine-turf mixture consisting of about 80% fescue and 20% agrostis by weight, choosing modern varieties from the scored character list published by the Sports Turf Research Institute, Bingley. Sow a mixture at the rate of 34 g/ m² (1 oz/sq yd). If the two species can be supplied ready for sowing separately, sow the fescue all in one direction at a rate of 27 g/m² (3/4 oz/sq yd) and the agrostis at right angles, using 7 g/m² (5 oz sq yd). To ensure good soil contact and help the seed to acquire the water necessary for germination, it is better for the seed to be worked into the top centimetre of the sand surface and then firmed into place by rolling. Irrigate if drought threatens to kill off the seedlings after germination has been achieved.

7. When the sward reaches a height of 40 mm (l1/2 in), roll to firm the soil round the roots. After vertical growth has been restored, top with a sharp mower set to a cutting height of 25 mm (1 in). Continue mowing at 25 mm (1 in), twice a week during the first eight weeks of growth, removing all clippings. After 2–3 cuts, fertilize as recommended for normal maintenance (section 10.5). Gradually lower the height of cut and mow correspondingly more frequently when preparing the surface for play.

10.4
Possibilities for further developments in the gravel bed approach

The gravel bed approach to construction is of special value under arid conditions where provision has to be made both for regular irrigation and the leaching away of salts. It can also find application in the construction of cricket tables, though the benefits of a gravel raft for drainage are much less likely to be required for a game played in summer-time on a heavily rolled, clay-rich topsoil.

The benefits of designs allowing for sub-irrigation through the basal gravel layer have yet to be fully explored. This approach has great potential to assist on critical occasions. For example:

1. to eliminate air for quick and effective consolidation of sand at construction time;

2. to more effectively saturate before leaching under arid conditions;

3. to ensure uniform seed germination and rapid establishment at time of construction or during pitch renovation;

4. to assist with cricket pitch preparation when the soil is deeply cracked and surface-applied water tends to trickle down past the bulk of the soil, instead of invading the clods to wet up evenly;

5. to maintain the exposed sand surface of a badly worn pitch stable for play.

Where provision for sub-irrigation through the gravel bed is contemplated, separate provision must be made for air-venting at the top of the gravel. Without this, trapped air will cause surface disruption if it is forced upwards in large bubbles through the topsoil. As an additional benefit, such an air-venting system will allow the gravel bed to be cleared separately after sub-irrigation, leaving the topsoil wet, e.g. to assist with sward establishment from seed.

10.5
Maintenance of fine, worm-free tur

Traditionally, autumn is the time for major renovation work and seeding. Spring is for boosting grass growth and removing weeds. However, completion of club tournaments often conflicts with the greenkeeper's need to begin major renovation work in good time to allow for a period of recuperative growth before all such work must cease for the winter. The alternative is to pursue a continuous renovation programme throughout the growing season, verti-cutting or lightly scarifying, spiking, over-seeding and topdressing a little every month, in harmony with the pattern of growth, rather than accumulating these tasks for one major effort in the autumn. Either way the players will be affected but, from the point of view of the sward, there is no doubt that the Tittle-and-often' approach is preferable, unless arrangements can be made for play to be switched to alternative greens. Much can be done to limit the extent of any interference with play by making adequate provision for skilled manpower, efficient equipment, and the supply and safe storage of materials.

10.5.1
Maintenance that should be given priority in the autumn

Timing

As the autumn renovation work may well involve considerable damage to the sward it should be started early enough to allow for topdressed seed to germinate and establish before the onset of winter. In England and Wales the growing season, as dictated by temperature, normally continues at sea level until the end of November, but with increasing altitude, growth is liable to slow down progressively earlier, stopping before the end of October at 300 m (1000 ft). For topdressing with fine sand, however, dry sand and a dry surface are essential and generally this cannot be relied upon after September, except in the drier east. For these reasons autumn renovation work should be organized for completion during September. At an altitude of 300 m (1000 ft), or in Scotland, or the wetter northwest of England, a start should even be made as early as late August.

Scarification and spiking

Nitrate, ammonium and phosphate ions all stimulate root branching and even do so when present as constituents of decomposing organic matter. Thus, any soil allowed to accumulate organic debris at the surface will encourage shallow rooting, quite apart from fostering surface wetness, disease, insect pests, and slowness of pace in a rolling ball.

It is inevitable where earthworms are absent that organic matter will tend to accumulate on the surface of the soil. Initially this will form a loose thatch of leaf debris but will subsequently settle down to form a root-bound mat. Therefore, steps to counteract this inevitable trend are essential in the worm-free conditions that we have to live with in our bowling green and golf green soils.

It would be best to look upon the sward-grooming procedures, carried out during the main playing season to improve the playing performance, as also contributing to less thatch accumulation. These are combing, brushing, wire raking, verti-cutting and light scarification. Verti-cutting should be aimed primarily at cutting vertically through the living tissue that escapes horizontal mowing by sprawling and should be carried out routinely throughout the growing season, e.g. at least once/month. Light scarification should be considered at best, as a crude form of verti-cutting that can be used to scratch through into the skin of organic debris that clings close to the soil surface as the thatch settles down. Light scarification, to be effective, must reach through to disturb this waterproofing skin, just scoring the surface of the mat layer. Deep scarification, by contrast, should be confined to major renovation work carried out in the autumn and may involve up to four passes in different directions. (On a cricket square it is vital to remove all the year's accumulation of thatch so that the clay-loam topdressing, required for the promotion of pace, can integrate directly with a mineral surface. Thus scarification on a cricket square can involve up to eight passes in different directions and considerable sward damage requiring subsequent re-seeding to repair.)

Solid-tine spiking or slitting are procedures used mainly with the aim of relieving soil compaction but with very mixed consequences. Unaccompanied by surface heave they can do no more than re-distribute the existing pore space. Carried out repeatedly they are liable simply to transfer any problem of compaction one stage lower. These procedures should not be carried out routinely, but with discretion, primarily to help with the renovation of a matted surface or to help with the infiltration of irrigation water and the incorporation of phosphate-rich fertilizers, seed and sand. Gentle pricking of the surface with a spiked Sarel roller to disturb and bypass any developing skin of thatch can help with aeration and surface water infiltration.

Hollow-tine spiking is typically the autumn procedure used curatively for long-term and accumulating benefit below ground. Ideally, this should be carried out annually, including the early years immediately after construction. The aim is to progressively remove more of each year's increment of root-bound mat, allowing it to be diluted with sand as it sinks within the profile, keeping the subsoil free-draining. On any green, the extraction of cores is necessary where a layer has been allowed to develop which is adversely affecting drainage. However, it can be effective only to the depth of tine penetration, and then much will depend on the nature of the soil beneath. At worst it will merely ensure that a buried, organic layer is helped to remain wet and anaerobic by having surface water diverted directly into it rather than through it. As with all other procedures, check to see that you have achieved what you intended. (See also Appendix G.)

Fertilizing

Spiking or slitting will open the surface to allow, first fertilizer, and then fine sand to penetrate. The autumn fertilizer should be low in nitrogen but high in phosphorus and potassium. Nitrogen (N) promotes lush growth, highly desirable in spring but too prone to frost damage and disease to be encouraged in the autumn. Potassium ions (K⁺), though retained by clay-rich soils, are liable, like the ammonium (NH₄)and nitrate (NO₃^-)ionic forms of fertilizer nitrogen, to be lost by leaching through free-draining, sandy soils. It could well be added, little and often, throughout the growing season and is applied in the autumn because of its value for promoting a degree of frost tolerance. All forms of fertilizer phosphorus are so poorly soluble when added to soil that they persist where placed and can be applied in large annual or biennial increments. This should be done after the soil surface has been cleared by scarification and opened up by spiking to allow incorporation, and when subsequent sand topdressing will ensure burial beneath the new surface.

A suitable, elemental, N:P:K ratio would be 4:7:7, or when expressed as N:P₂0₅:K₂0 (unfortunately also casually referred to as the NPK ratio) would be 4:16:8. There is no real advantage in every year using an organic carrier such as peat; most fine turf swards suffer from excess surface organic matter, not a deficiency. The aim during application should be to work this autumn fertilizer off the surface into the spike holes. Left on the surface, the insoluble forms of fertilizer phosphorus will stay there to stimulate surface rooting. Buried it will encourage root branching at depth; 35 g/m² (1 oz/sq yd) being sufficient.

Sand topdressing

Topdress the scarified, cleaned-up and fertilized surface with an approved sand, at something like 4 kg/m² (7 lbs/sq yd) if this is tackled only once a year. The purpose is to bury the fertilizer phosphorus, bury any residual organic debris, bury roots and re-true the surface. The sand, especially for the bounce-deadening character required of golf greens, should be fine and, normally, lime-free. It should be of a uniform particle size, like a plasterer's sand, and the particles should be rounded rather than the sharply angular and coarse material preferred by horticulturalists for potting composts. For bowls these requirements can be relaxed a little as a firm surface would not be unacceptable.

All of this will help to provide an open, yielding surface for rapid drainage and fast pace rather than a surface that may settle to become rigid and fiery, encouraging bounce. Choice of sand, therefore, is vital and doubtful samples should be sent for testing before application.

Pace is a matter of sward composition, vertical growth, mowing height, surface dryness and the absence of the spongy effect caused by a surface mat of thatch and superficial roots. The holding character required to stop a golf ball, that is pitched high on to the green, is better sought by proper maintenance and correct choice of sand than by the sogginess of a dampened mat. For application, the sand should be perfectly dry or, when brushed, it will smear over the sward instead of working into the base. Ideally it should be applied dry, onto a dry surface, systematically metered out in appropriate sized heaps and then luted into the base of the sward. The wider the lute the better as it will act as a straight edge to scrape sand off the high spots and leave extra in the hollows, so smoothing out local irregularities. This will make close mowing possible without scalping, discouraging the spread of moss and truing the roll of the ball. A 3 m (10 ft) lute would not be unduly wide for a flat bowling green but a drag mat or smaller lute will be required to accommodate the gentle undulations that are a desirable feature of a golf, or crown bowling green. Roll to consolidate.

The emphasis on sand as a topdressing is deliberate. It may be modified occasionally by the inclusion of a low fibre compost, such as milled seaweed, or a durable, particulate form of organic matter, such as a fine (less than 2 mm) grade of crushed lignite. This will become necessary if the zeal of the greenkeeper in scarification and sand topdressing leads eventually to a topsoil so raw and sandy as to be organic deficient.

After topdressing, the green will appear to be a sea of sand, but a shower of fine rain or an equivalent irrigation, will settle the sand and allow the grass to show through. On no account should the sward be left buried under a complete covering of sand or it will be smothered. For this reason, topdressing with sand should never be left so late that soil conditions are too wet, and the temperature too low, for recuperative growth.

Disease, worms and insect pests

Where drainage is good, irrigation not overdone, appropriate grasses sown, thatch removed and luxury uptake of nitrogen avoided, as much as possible will have been done to avoid undue trouble from the competitive efforts of disease and pest organisms. Thereafter, specific, early, curative treatment should follow clear visual evidence of trouble, using spot treatments when the symptoms are well defined and localized.

For close mown, fine turf, earthworms, unfortunately, must be excluded. Normally this is an inevitable consequence of the removal of clippings limiting their food supply, and the acid conditions that develop in a noncalcareous, sand soil, leached by high rainfall and acidified by the application of fertilizers containing sulphur. In addition they will have been killed by many of the chemicals used against pests and diseases, e.g. benomyl (as in Benlate), thiophanate-methyl (as in Mildothane), and malathion (as in Malathion 60). In special circumstances, generally where lime in the sand keeps the soil pH up, some earthworms will persist and require elimination by repeated application of a proprietary wormicide.

Over-seeding

Do not expect too much from over-seeding into fine turf that is frequently close mown. Seedlings may well appear, borne aloft on the limited food reserves available within the seed. But will they be allowed time to become independent and build up the reserves required for re-growth following relentless close mowing? It would not be advisable to start mowing a newly sown lawn immediately growth exceeded 6 mm (1/4 in)! With normal seeding, successful establishment requires delaying close mowing until at least two cuts have been taken at not less than 25 mm (1 in). This means that, if successful establishment is to follow on from seedling emergence, use must be suspended for at least 4–6 weeks during the growing season. Again, unless spare greens are available to switch to, the only alternative is to learn to live with the consequences of the relentless, self-seeding activities of Poa annua.

Over-seeding is necessary both to repair damage and keep abreast of the very efficient dispersal mechanisms of natural competitors. Well-managed, fine turf in Britain tends to be dominated by some combination of agrostis, fescue and the natural competitor, annual meadow-grass. The fescues used are fine, needle-leaved grasses, well-suited to cope naturally with partial desiccation and burial. However, being a type of grass that regenerates vertically from near the surface, it is the lawn grass that is most punished by close mowing. Agrostis and annual meadow-grass tend to escape because they can be more prostrate in growth, regenerating laterally over the surface, or just within the soil. When close mowing is combined with frequent irrigation, fescue loses out to the greater vigour of the other two. The balance between agrostis and annual meadow-grass is shifted in favour of annual meadow-grass when luxurious supplies of water and nutrients are applied and the constant, natural dispersal of annual meadow-grass seeds is not challenged by regular over-seeding with desired species.

There is much to be said for keeping fescue and agrostis seed supplies apart, sowing each species separately. Alternatively, use a combination of two varieties of agrostis, complementary in their peak periods of performance.

When ordering and applying seed keep the following rough estimations in mind:

The much larger seeds of fescue are probably best introduced in autumn, buried in coreholes or slits and under sand topdressing to ensure good seed/soil contact for the absorption of water. Agrostis seed, being very small and having a very limited food reserve, should not be buried deep, merely pressed into the surface at any time during the growing season when the soil can be maintained moist (e.g. by covering and/or irrigating) until germination is achieved.

As Poa annua seeds all the year round, even at close-mowing height, and does not require burial to germinate, it is exceptionally well equipped to invade any bare spots. The challenge, therefore, is to ensure that there is always some agrostis seed in place to compete. Hence, there is potentially some virtue in including at least some agrostis seed with all sand topdressings applied during the growing season.

A new development which promises to greatly assist sward repair and establishment from seed is the recent appearance of dry, pregerminated seed. This offers the possibility of uniform germination in four days without the difficulties associated with handling wet, pregerminated seed. The dry, pre-germinated seeds can be stored after treatment for many weeks, without loss of viability and, except for appearing to be at some risk from residual effects of herbicides such as paraquat, can be sown in the same way as ordinary seed. The extra cost of the pre-germination treatment can be off-set against the possibility of a reduced seeding rate because of the rapid, more uniform germination.

For equal numbers of seeds per unit area, the weight of fescue seed required is ten times that of agrostis. When uniformly spread, 1 g/m² of agrostis is equivalent in seeding rate to 10 g/m² of fescue, each providing six seeds per square inch (6.5 cm²). Use this information to adjust seeding rate to visual evidence of need. For example, making a generous allowance for the practical difficulties of achieving a perfect distribution, try 1/2 g/m² of agrostis seed (approximately 1 oz for an area 4 yards by 4 yards) mixed into each sand topdressing applied during the growing season. Alternatively, apply separately each autumn 1 g/m² of agrostis and 10 g/m² of fescue (approximately 1 oz and 10 oz respectively for an area 6 yards by 6 yards.

Instant repair of localized sward damage

Fuel spillage, animal urination, mower scalping, weed removal, etc. may cause localized damage requiring instant repair by turf replacement. This points to the value of a small area of turf nursery on site, conveniently located where the soil, sward and maintenance can replicate that on the green. A neatly cut, 50–100 mm (2–4 in) deep, stable, turf patch can then be instantly inserted, using a turfing iron or, where a core 108 mm (41/4 in) in diameter will suffice, a golf hole cutter.

Summary

The normal autumn renovations should proceed in the following sequence: mowing, scarification, removal of debris; spiking or hollow-tining plus removal of cores; over-seeding and fertilizing; sanding, brushing and luting to level out and integrate; irrigating if necessary to finally settle in.

10.5.2
Priorities for maintenance in spring and summer

Timing

Soil temperature dictates the onset of growth in spring and, apart from maintaining good drainage, the greenkeeper can do little about this. In general, growth starts about the third week in March but may be a week earlier in the south of England and at least a week later in the north. However, altitude can have a marked local effect. At 1000 ft (300 m) the onset of growth may be delayed for an additional three weeks, until the middle of April. Therefore, there are special difficulties for maintenance at altitude, both in the autumn and in the spring, and due allowance should be made for this in the late recovery of the greens.

To enable some account to be taken of variations in season from year to year, it is worthwhile installing a soil temperature recording thermometer in an area of maintained sward free from vandalism. In general, a soil temperature of 8°C (46°F) at 25 cm (10 in) depth can be taken to indicate the start of the growing season. However, beware false springs and delay the application of seed and fertilizer until soil temperature reaches the order of 10°C (50°F) at 25 cm (10 in), when growth really begins to take off (Appendix A).

Scarification

According to the amount of grass growth and mowing over winter, there may be some need to clean out the base of the sward and lift any sprawling horizontal shoots. Use a scarifying wire brush or verti-cutting mower to clean the surface top without penetrating the soil before fertilizing to promote new vertical growth in the spring. Deep scarification would not be advisable in the spring as the dry conditions of summer will discourage the healing over of any score lines.

Weed and moss control

Spring is the best time to weed kill as some weed killers damage young grass and, in any case, weeds are most susceptible when new leaves are exposed and the growth is thin-walled and lush. The grass, when growing vigorously, will rapidly fill in. The same can be said for moss killing though moss should not be there if maintenance and management are correct. Moss has no true roots and cannot compete; it can only fill in where damage such as tear wear or scalping has been caused and no immediate steps have been taken to achieve the necessary repair.

If certain weeds continually reappear consideration should be given to the possibility that these may originate either in the topdressing, Spergularia (Sandspurrey) being typical of dune sand, or in worm activity re-cycling buried, viable seeds from the underlying soil.

Fertilizing

The spring fertilizer should mainly be nitrogen to promote green growth. On very sandy media, however, potassium which, like nitrogenous fertilizers, is highly soluble and very prone to leaching, should also be regularly applied during the growing season. A suitable nitrogen (N) to potassium (K) ratio would be 12:8. When expressed as nitrogen (N):potassium oxide (K₂0) this becomes a ratio of 12:9. Apply on three or four occasions between the end of March and mid-August, using a rate of 35 g/m² (1 oz/sq yd) on each occasion. Do not apply in dry weather.

Avoid fertilizers that include much phosphorus during the growing season if they cannot be incorporated by burial. The buried autumn application will persist to carry the sward through.

Sand topdressing, light scarification and/or verti-cutting

With adequate staff and the facility to put greens temporarily out of use, topdress with 1 kg/m² (2 lbs/sq yd) of topsoil sand on each occasion after fertilizing during the spring and summer. This will cut down the need for a large autumn application. A policy of little-and-often is to be preferred. As already indicated, it would be advisable to use these occasions to include the recommended over-seeding with agrostis.

Prior to application, ‘prick-spike’ and recondition the turf surface with a verti-cutting mower or a wire brush type of scarifier to remove thatch. This will also provide a better seed bed and help any topdressing to integrate with the existing soil. However, as in the spring, do not cut into the soil as any desiccation will cause the cut to open up and persist, upsetting the true roll of a ball.

Prior to mowing, always give consideration to grooming. That means not just verti-cutting but combing and brushing to lift thatch or sprawling grass up to mowing height. For best effect, and certainly when preparing for a tournament, these operations should be repeated in two directions, each time finished off by mowing.

Mowing

Mowing should never be so low as to scrape the surface and should never involve removal of more than 1/3rd of the grown height. Since growth may easily achieve 25 mm (1 in) per week at the peak of the growing season this means that a maintenance height of 6 mm (1/4 in) can only be achieved, without weakening the grass, if cut each day, i.e. after 3 mm (1/8 in) of growth. This certainly applies during May, June and July. Removal of more than 1/3rd of the grown height cuts into reserves required for tillering or vigorous regrowth and most certainly affects the vigour of the vertical-growing grasses, in particular, fescue.

Cutting daily at 3 mm (1/8 in) should be considered only for special tournaments, and then, only if the mower is perfectly set and the surface sufficiently smooth to avoid any risk of high spots being scalped. Severe mowing, i.e. close mowing at infrequent intervals, will weaken the sward and encourage the invasion of moss. Far better to concentrate more time on grooming and increased frequency of mowing rather than lower the height of cut.

Where close mowing cannot be achieved without some spots being scalped and others being left too lush, steps should be taken steadily to improve the grading of the surface. High spots can be progressively lowered by extracting cores with a hollow-tine fork and not filling back with topdressing. Low spots can be raised by selectively topdressing or by turves being undercut and folded back to allow for extra sand to be inserted below.

Good equipment, skilfully used and properly maintained, is essential. Nothing is more disastrous to the sharpness of a mower than mineral matter sticking to the grass at cutting height. This risk is most severe after scarification and sand topdressing, especially if regular increments of fine sand are applied during the growing season, following each application of fertilizer. However, trouble can be avoided, both from the sand, and from the fertilizer scorching in dry weather, if these various topdressings are washed into the base of the sward by irrigation.

Irrigation

Facilities for irrigation are of value but should only be used to thoroughly soak at infrequent intervals. That is to say, it should only be used for the benefit of the grass to avoid desiccation, to wash in fertilizer or to settle in a topdressing of sand. It should be regarded as an aid to maintenance and should never be controlled by players seeking to influence the pace of the greens. Little-and-often irrigation onto a dry soil will encourage shallow rooting and make the sward particularly sensitive to drought, disease and limited nutrient supply. However, little-and-often can be justified if started before the soil has dried out in depth. This should keep the whole soil moist and, although such a moist regime will encourage annual meadow-grass and discourage fescue it will not promote surface rooting, nor risk ‘dry patch’ (section F.3) and desiccation.

A viable compromise between these two extremes is to delay irrigation until there is a marked fall in the clippings harvest when mowing. Such a growth check during the growing season indicates that the moisture deficit, though still well short of wilting point, when death would occur, has reached the stage when cell enlargement and, therefore, growth is affected. At this point, irrigate to re-wet the top 50–75 mm (2–3 in) of the soil by 5–6 applications of 2–3 mm (1/10 in), stopping only long enough between applications to prevent surface flooding leading to wasteful runoff Supplement with a wetting agent where there has been a history of dry patch problems. Thereafter, until the drought is broken, apply a single application of 2–3 mm (1/10in) daily to replenish at about the average, daily rate of evapo-transpiration loss in summertime. This approach will not discourage deep rooting or the maximum exploitation of the pace potential of a dry surface. What is vital is the skill to recognize the growth-check symptom and the ability then to react appropriately. With the advent of simple probe moisture meters this could now be more easily monitored.

10.5.3
Note for home-lawn owners

Too often the home-lawn owner gets carried away with the immaculate appearance of the sward on the local bowling green or golf green and jumps naively to the conclusion that this is all a consequence of choosing the correct seed mixture, fertilizing, lowering the height of cut and removing all clippings. It is not always appreciated how devastating is the effect of mowing at 6 mm (1/4 in), just once a week, or, worse still, once a fortnight. This alone leads to weak growth of grass, loss of fescue and, in the absence of earthworms, infill by moss, annual meadow grass and Yorkshire fog plus, with earthworms, daisies, plantains, and a wide range of other broad-leaved weeds. Most week-end gardeners would do better to maintain a sharp mower, raise height of cut to 25–35 mm (l-l1/2 in), and allow clippings to fly when they are fine enough not to smother. Then, in addition, lime, fertilize and weed kill in moderation, welcoming the assistance that earthworms can give with drainage, incorporation of organic residues and efficient root exploitation of the soil in depth (section 11.4).