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MENDIP TIMES
The magic of mulch
WHAT is mulch? It is probably best described as a surface dressing between plants which has so many useful attributes. It is very much a “gardener’s best friend”! Homemade garden compost can be used as a mulch, but unless you are an expert composter, it is likely to contain a lot of With MARY weed seeds. However, it will have many of PAYNE MBE the other benefits. Well-rotted horse or farmyard manure is similar and may introduce both weed seeds and active roots of perennial weeds such as bindweed, which you have hopefully avoided putting in your garden compost heap. This is especially so if it has been stored outdoors. A mulch made from straw is available commercially in many garden centres and this is an excellent product, providing many of the benefits, without the associated weed problem, and the bonus of discouraging slugs and snails. For vegetable plots where “looks” are less important, a layer of cardboard can be used, or even several sheets of newspaper covered with a layer of grass clippings. Mushroom compost is excellent, but will decay within 12 months and need replenishing. Woodchip mulch is ideal as it decays slowly and tree surgeons are often only too pleased to get rid of shreddings. All organic mulches have the bonus of breaking down to provide some nutrition, but there are so many other advantages, particularly for those looking to make gardening easier for yourself and better for your plants. So, what makes mulch so useful? One of the huge advantages, particularly in these times of climate change and summer droughts, is a mulch layer which will help prevent undue water loss by surface evaporation from the soil. This occurs not only in sunny weather but also during periods of drying winds. Fine grade woodchip mulch can be used on pots to reduce evaporation and therefore reduce watering. Some commercial nurseries use shredded miscanthus grasses for this purpose as it helps prevent the germination of hairy bittercress, the scourge of container plants. The other main bonus of mulch is that a minimum depth of 5cm (2”) will prevent the germination of weed seeds. It does this by cutting out the light from the surface of the soil, so seed germination is inhibited. This is only effective if a weed-free material is used for the mulch, so not homemade compost, or farmyard manure. A layer of organic mulch will not prevent perennial weeds, such as ground elder, couch grass, and bindweed from pushing through from persistent underground roots, but adding a layer of cardboard will inhibit them somewhat. I always recommend a minimum 5cm layer of woodland mulch (wood chip) to be applied immediately after an area has been planted. This will inhibit seed germination for a period of about three years. If home compost, farmyard manure or mushroom compost is used it will decay within 12 months and need replenishing. Mulch will gradually improve your soil structure by adding nutrients as it breaks down. Even a clay soil regularly mulched will show significant improvement quite rapidly. It is sometimes claimed that woodchip mulch will lead to a deficiency of nitrogen. This is not the case if it is put on the PAGE 54 • MENDIP TIMES • MARCH 2022
surface of the soil. If it is incorporated into the soil, then the bacteria and fungi that break it down need nitrogen. To do this they take it from the soil. If you a have a garden shredder, then the chippings can be put immediately on the surface of a border. They will rapidly lose their freshly shredded colour. Shreddings from conifers are more acidic that those from broadleaved plants but can still be used, especially around rhododendrons and other acid loving plants. Other advantages include preventing rain splash, so it can be used instead of straw for strawberries, or spread beneath roses after leaf fall to help prevent black spot disease. It helps prevent erosion on newly planted slopes and may help prevent diseases. Research has shown that wood chips from willow may reduce the incidence of apple scab disease. The salicylic acid appears to prompt a disease fighting immune response. While in Australia avocado pear plantations mulched with woodchip helped prevent the devastating Phytophthera disease which is currently causing problems worldwide. Woodchip from eucalyptus has fungicidal, insect repellent and antimicrobial properties when used as bedding for poultry and animals. The use of woodchip on land contaminated by oil or diesel spills helps clean the soil by encouraging the fungi responsible for degrading such materials. Tender plants can be insulated by a generous layer of mulch whilst all treated areas will benefit from the soil insulation. One concern may be that the woodchip you purchase has come from diseased trees but the evidence so far is that it does more good than harm, but should not be dug into the soil and should be kept away from the bark of trees. A bark mulched newly planted area looks more aesthetically pleasing and by the time the mulch has decayed the plants themselves should have covered the ground and excluded light to help prevent weed seed germination. Planting any area infected with persistent perennial weeds is to be seriously discouraged. The National Trust and Royal Horticultural Society both use pigs to clear land prior to planting! Virtually the only downside to mulch in a garden is that birds, especially blackbirds, like to scratch and flick the bark onto paths or paving in search of the slugs and worms hiding beneath. Don’t be alarmed if a layer of white threads grows beneath the surface of a woodchip mulch. This is simply the “root” systems (mycelium) of the saprophytic fungi that are breaking down the mulch. You may get the occasional toadstool as well. Composted bark is frequently used in “peat free” or “peat reduced” potting compost these days and often leads to a flush of toadstools.
