PUBLISHED: 08:11 28 March 2014 | UPDATED: 08:53 28 March 2014
Sue Adams on a good way to improve your soil!
My ideal soil structure is a silty loam and a pH of about 6-6.5. This is a soil which is slightly acidic and friable and incorporates plenty of organic matter. You can dig it soon after heavy rain as it drains well and it rarely dries out completely. I was blessed with this type of soil when I used to grow vegetables on the alluvial flood plain of the River Otter in Devon. Friends close by were forced to work heavy, red, East Devon clay and envied my good luck. However, this ideal soil is hard to come by naturally, and for most of my gardening career, I’ve needed to work my earth to encourage the characteristics I want. To manipulate the soil in this way you need to understand the role and application of mulches and how they assist nature in that search for balance.
Mulches are generally applied as thick blankets (sometimes up to three or four inches deep if you’re using them to prevent weeds) of organic matter, packed around plants. Organic mulch is conventionally well rotted garden compost or animal manure, leaf mould, spent mushroom compost, composted bark or a combination of several of these. You can also use sheep fleece, old carpets, gravel, horticultural fleece, black plastic and branded products such as Mypex and Vitax – which is a form of biodegradable woolmoss. The mulch you choose depends on the purpose, cost, and aesthetics.
Organic mulches will tend to be the mulches of choice for smallholders. They can cost nothing with a bit of forward planning and, over time, disappear into the soil and enrich it. The important thing with all of these organic mediums is that they’re thoroughly composted and that you apply them to a clean soil surface. The composting process, which can easily take a couple of years, does two important things: it kills off weed seeds, and turns the organic matter into small particles, which the soil can incorporate into itself with minimum effort. Compost adds essential plant nutrients and humus, in safe quantities, to soil. If you add uncomposted organic mulch to your soil, it might leach the goodness out of the soil as it continues to decompose, undermining your attempts to improve the soil’s quality.
Maintaining the cycle
If you consider the life cycle of plants, it’s easy to see how important it is to put back into the soil what you’ve taken out. As a plant grows, it takes nitrogen and other nutrients from soil to assist the growth process. The plant dies, falls onto the ground, and over time, rots down. Animals may also graze on some of the plant material and help add nitrogen and other nutrients as they return it to the earth via their excrement. The process is slow, but it balances what is taken from the earth with what is returned to it.
On the smallholding, however, we grow things in an unnatural manner. We grow concentrations of specific plants, sometimes in the same place for years in a row, and we expect high yields. We clear away or harvest dead plant material, depriving the soil of the nutrients it needs to regain its strength, and we tend not to let livestock onto vegetable beds, dropping manure. Because of all this, we need to put back into the earth what we’ve taken from it. Hence the compost heap, manure heap or leaf mould bin. By returning composted plant material as a mulch, you ensure that the soil is replenished and not depleted by the composting process itself. You also protect the soil from erosion, evaporation of water and invasion by nutrient-hungry weeds.
Nature also has a method of ensuring that rotted organic matter is incorporated into the soil, instead of remaining on top of it – the earthworm. The worm drags rotting leaves into the ground and the mulch on top is incorporated – without you lifting your spade – into the soil beneath. This is the principle behind no dig beds, raised beds or Chinese beds, where each year a top dressing of mulch is applied and gradually incorporated into the earth, improving pH, structure, drainage and fertility. Your mulch is also your fertilizer, protecting, nourishing and improving structure while adding the chemicals which encourage leaf, root and fruit growth in an environmentally sustainable way. Remember, though, not to mulch right up to the collar of the plant – if organic mulch comes into contact with the plant stem, there’s the danger the plant itself will rot.
Your mulch can also help to manipulate pH. Animal manure has a tendency towards acidity, so over time will lower the pH and make soil slightly more acidic. Spent mushroom compost, on the other hand, is alkaline and will slightly increase the pH if applied consistently.
Mulches can also do much more to help keep your soil the way you want it. If you have an area you want to keep free of weeds, or as moist as possible, you could try using old wool carpet or sheep wool. It’s a natural material which can eventually assimilate into the ground, adding to the humus content. Dense enough, it will stifle any weed growth so that your soil is still clean when you begin your planting programme. It will also help prevent evaporation. You can put a ring of carpet or fleece around the base of a young tree to stop weeds competing with the tree for nutrients and to help preserve moisture. Remember though that wool isn’t composted, so the earth will have to work hard to draw any nutrient value from it.
Coarse bark is also useful as a weed suppressant. It hasn’t been broken into small pieces by the composting process so it stays on top of the soil longer and, like wool, isn’t an attractive host to weed seedlings.
If you have an area of ground covered in weeds and you have plenty of time, a thick black plastic sheet used as a mulch will clean it for you. Weight the plastic down with stones so no light can get under it and the wind can’t disturb it. Leave it for a year (or more with stubborn perennial weeds) and the ground will then be ready to dig.
A mulch of horticultural fleece allows light to penetrate. It will warm up the soil so you can get ahead with planting, and can protect soil and crops from attack by specific pests.
A mulch of gravel or grit can be attractive, help to prevent plant rot and act as a pest deterrent. I’ve used it to stop a particular patch of earth becoming a cat latrine. It can be dry and uncomfortable for slugs to cross and so deter them. I’ve seen a mulch of crushed eggshells used for the same reasons.
Sharp sand or fine grit can help lighten very heavy soil. Incorporate it within an organic mulch to create a cocktail tailored to your own soil conditions and requirements. Each year earthworms will pull it into the ground along with the plant matter. Otherwise, you can dig it in.
Strawberries, I’m sure, were so named because they were mulched with straw to protect the berries from damp and slugs. Nowadays black plastic, far less romantic, is laid on clean, moist ground and the plants are planted directly through holes in it into the ground. The plastic keeps the ground weed free, conserves water and keeps the berries clean and dry. It can remain for two or three years before it starts to decompose, by which time you will be ready to move your strawberry plants anyway.
Mulches are natural allies when growing plants for ornamental purposes or for food. I use them because they improve, feed and protect soil with minimal chemical intervention, while allowing me to recycle the by-products of production. Above all, they work with nature instead of against it.
This article is from the May 2006 issue of Country Smallholding magazine.
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