Over winter it is possible to collect a stockpile of woody prunings. The ideal way to deal with this is to shred it and add it to the compost heap. However, to create the traditional ‘hot heap’ you also need similar volumes of soft green material or grass clippings, not so common in winter.
Another way of dealing with the woody prunings is to simply shred them, pile them up for at least six weeks to allow them to weather and then use the wood chip as a mulch for pathways or as a weed suppressant on borders. Bark and woody tissues of trees and shrubs are toxic to seedlings if used fresh as they contain naturally occurring toxic substances such as monoterpenes and tannins. These phytotoxins are reduced to innocuous levels if the moist chippings are stacked as suggested. When heaped, the chippings are invaded by naturally occurring thermophilic bacteria that can reduce the monoterpene content by 75 percent, making it suitable for horticultural purposes. If the heaps are large enough, most of the common pathogens that might be present will also be killed by the high temperatures generated.
As an alternative you can create a woody compost heap. This can be a freestanding pile or you can make a structure out of woody prunings. Use large woody off-cuts as corner posts. At each corner have two posts with a small gap between them. Use prunings larger than finger thickness to form the walls (pushed down firmly between the corner posts) and thinner material can simply go into the heap cut into 30cm (12in) lengths; don’t worry about shredding them. A heap of pure woody prunings could take more than five years to rot, including part of the walls. Soft prunings or grass clippings can be added and they will speed up the process. Try not to disturb the heap too much as it will become a haven for all sorts of animals - such as beetles, centipedes, slow worms, grass snakes, hedgehogs etc.
Shredder types
Most domestic shredders can cope with woody stems less than 35–40mm (1 - 1 1/2in) in diameter. Larger branches can be cut into lengths and stacked to make wildlife habitat piles. Whether to hire or buy a shredder really depends on how much use you anticipate making of it. For gardens with a lot of twiggy material from hedges, soft fruit and shrubs, it may be worth buying an electric-powered shredder. These are relatively quiet and effective on thinner stems. In gardens occasionally generating thicker material such as tree branches, hiring a petrol-powered shredder annually may be more economical.
Safety first
Always ask for a demonstration if hiring a shredder, and refer to the manufacturer’s instructions after purchasing one before using it. Gloves and goggles are essential to protect hands and eyes from flying debris. Never try to force material through the shredder or unblock jams by putting your hand near the moving parts: turn off the power first. Many shredders can be unblocked by simply putting them into reverse.
Paul Alexander