Composting prunings

An excess of woody waste can be a problem for gardeners because it may take more than two years to decompose in a compost bin. This is partly because large stems tend to dry out quickly, reducing decomposer activity, and partly because fungi, which tackle the wood, are slow workers. In the past, prunings were burned and the resulting potash-rich ash was used to feed the soil, but bonfires cause harmful air pollution and are now illegal in many areas. More eco-friendly methods include transforming prunings into a useful mulching material or stockpiling logs to make homes for wildlife.

Recycling woody waste

Twiggy tree and shrub prunings can provide the carbon-rich bread in the compost sandwich, but because they take a long time to decompose you should only include them in thin layers. In addition, stems that are more than ¾in (2cm) in diameter will probably not compost down within a year, even in a hot heap, leaving you with large lumps in your black gold. This is because wood, like autumn leaves (see Making Leaf Mold), has a high lignin content which fungi break down very slowly. Large branches also have a relatively small surface area for the microbes to work on; the best plan is to shred them, which creates more surfaces and helps to speed up the action. Woody stems and branches left intact allow large air gaps between them, too, which causes them to dry out and slows down decomposition.

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A large hedge may produce too much woody waste to compost in a mixed bin.

Shred and mulch

If you produce a glut of prunings in the winter or spring, or have hedges that generate large quantities of woody waste, consider hiring or buying a shredder to create wood chips. Prunings taken from living plants will contain nitrogen as well as carbon, and are the best sort to shred and add in thin layers to a bin—hot composting is an ideal way to use them. Alternatively, you can compost wood chips on their own in a tall, thin bin that uses the weight of the stacked material to compress it and remove large air gaps. Using this method, the wood chips will take at least two years to break down into coarse-textured compost, though adding activators such as urine will halve that time. You can compost unshredded prunings, but only if you are prepared to wait three years.

Another way to use wood chips is to apply a 2–3in (5–8cm) layer of them over the soil to create a weed-suppressing mulch around fruit trees, or to make a naturalistic pathway through the garden or around vegetable beds.

TOP TIP If you do not have sufficient woody waste to warrant hiring a shredder, ask neighbors if you can pool your waste material with theirs and share the cost to make it worthwhile.

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Use large quantities of shredded prunings to make a path around vegetable beds or through an informal garden.

Homes for wildlife

Large logs and thick stems cannot be shredded or composted easily, but they are still a valuable asset to the garden. Log piles make the perfect homes for many types of wildlife such as beetles and hibernating frogs and toads, which prey on insect plant pests and are a benefit to the gardener. Simply pile up your logs and branches in a quiet corner in partial shade, pushing twigs and leaves into the gaps. Avoid deep shade or full sun, which may be too cold or hot for invertebrates and other wildlife.

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Stack spare logs and branches in a quiet area to create a wildlife habitat for invertebrates and hibernating amphibians.

Making Compost | COMPOSTING PRUNINGS

The HÜgelkultur method

This method works on a similar principle to trench composting but instead of burying your green waste you create mounds, known as hugels, of woody materials, green waste, and soil, which you then leave to decompose. This system of composting was described and named in the late 1970s by the German horticulturalists Hans Beba and Herman Andra, although there is historic evidence of its use hundreds of years earlier in Eastern Europe.

Start by digging a trench about 5ft (1.5m) wide and 12in (30cm) deep in a sunny area—it can be as long as you require. Set the soil aside. Place logs and branches at the bottom of the trench and add a 8–12in (20–30cm) layer of nitrogen-rich greens, such as kitchen waste or grass clippings, along with smaller branches, twigs, wood chips, and leaves, to fill the gaps. You can also use any turf removed when digging the hole—turn it root-side up and place it over the logs before adding the nitrogen-rich greens and twiggy materials. Then apply a 4–6in (10–15cm) layer of semi-mature compost or manure. If you have sufficient material, add another layer of slightly smaller logs and branches and infill as described above. Finally, cover the mound with the soil you initially excavated from the hole.

The decomposers will rot the contents and reduce the mound to half its height when the composting process is complete. This may take a year or more, but meanwhile you can plant into the soil covering the mound. Warmth generated by the decomposers speeds up growth, while the water-retentive areas on the sides of the mound and free drainage at the top suit many plants. As the mound rots down, it also delivers nutrients to the roots.

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The Hügelkultur method uses waste wood and prunings.

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