Mulches
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A late autumn mulching benefits your garden just as much as mulching in the spring. But instead of helping to retain moisture and prevent the topsoil being blown away, it works by preventing the heavy winter rain beating the soil down and washing it away. And in cold areas the mulch acts as an insulating layer that lessens the depth to which frost penetrates.
Mulches have many additional benefits that aren’t always appreciated until you’ve been mulching for a while. Building up a layer of fine surface soil with a high humus content encourages vast numbers of earthworms to develop. The worms drag the surface materials into their tunnels to digest it; thereby taking the humus and nutrients to lower levels, while the tunnels themselves improve soil drainage and aerate your plants’ roots.
Other beneficial soil organisms will also thrive in well-mulched soil, helping to raise the fertility of your garden. Less desirable garden wildlife, such as cutworms, slugs, snails and slaters may also find a comfortable home in the mulch, but the improved health of your soil will better enable your plants to cope with these pests.
Weeds are far easier to remove from soft friable mulch than from hard compacted soil. Simply running a hoe through the mulch every week or so will kill the weed seedlings before they have a chance to establish themselves.
But what to use as a mulch? Well, I still favour composted fallen leaves from deciduous shrubs and trees, perhaps mixed with some conifer needles. Of course, in deciduous forests autumn mulching occurs naturally with the falling of the leaves, so all we’re really doing with this type of leaf mould is imitating nature, or perhaps giving it a helping hand.
The range of possible mulches is huge. The easiest for most gardeners is simply to use their own home-made garden waste-based compost chopped up finely with a spade and spread around the garden. The more leaf mould in the compost the better it will be.
It’s not just green matter that can be composted. Sawdust, bark, dry pine needles, spent potting mix and even newspaper can all be composted to make a less nutrient-rich drier compost that makes a good mulch.
Wood products, such as bark and fresh sawdust, will require considerable amounts of extra nitrogen to make them rot quickly. Add about 500g of urea or 1kg of sulphate of ammonia for cubic metre of material. Extra fertilisers can also be added if you wish. Your compost bins will need to be able to hold at least 2 cubic metres, preferably more, in order to build up a good heat. Allow four to six months to compost, turning once a month.
In the larger cities, councils may run garden waste recycling programmes that produce high quality compost suitable for use as mulch. Here in Christchurch, the city council’s Envy compost/mulch has proved very popular despite initial concerns that it would be hard to monitor the herbicide content of the home garden waste from which it is made.
Mushroom compost is another readily available instant mulch that has its devotees despite its rather high lime content. I like its texture but not its rather unpredictable composition and state of decomposition. I’d sooner use it (and other products like chicken shed scrapings, seaweed, straw and sawdust) as a compost heap ingredient so that the additional composting can provide time to calm it down.
It’s even possible to use stone, shells and other inorganic products as mulches. Naturally, they’re not going to add any humus to the soil but they will help to lessen the damage caused by heavy rain, strong winds and widely fluctuating temperatures. Green mulches, such as ground covers and grasses grown around orchard trees have a similar effect, though they will of course remove nutrients rather than add them.
Whatever you use as a mulch, at least use something. Nothing lessens soil fertility and damages its structure more quickly than leaving bare soil exposed to wind and rain erosion, compaction and dehydration.
Copyright Geoff Bryant
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