Mulches

Mulching brings many benefits over and above its primary role in improving the soil. It gives your garden a neat, well-tended finish and reduces the amount of time and effort you need to spend on routine care.

Extreme weather is unkind to bare soil. Hot sunshine and winds dry and harden the surface, which causes heavy ground like clay to crack. Pounding rain turns the surface to a caked crust, and it washes away plant foods and even the topsoil itself. To protect your soil from these effects, cover the surface with a mulch.

Depending on the material you use, mulching can also:

• Improve soil texture
• Increase the soil's ability to retain water and nutrients
• Suppress weeds
• Provide plant nutrients
• Deter some pests
• Protect plant roots from temperature extremes, including moderate frost
• Give a decorative finish to beds or containers, especially for alpines.

Using Mulches

All bare cultivated soil benefits from mulching. Mulches tend initially to preserve the conditions they cover; for example, moist soil is prevented from drying out, while cold soil takes longer to warm up. So the best times to mulch are late spring, when soil temperatures are rising, and early autumn, before they begin to fall. Before covering the soil with a mulch, remove weeds, apply any fertilisers and ensure that the ground is thoroughly moist.

Types of Mulch

There are permanent inorganic mulches, such as gravel and shingle, and seasonal mulches, which include the various organic materials applied while plants are growing as well as being forked in later to improve the soil. There are also synthetic sheet mulches that are effective at suppressing weeds but which tend to look unattractive.

For maximum benefit spread loose organic mulches 5-10 cm (2-4 in) deep, depending on the plants. Young perennials, for example, need only a shallow mulch, which can be topped up as the plants develop, whereas shrubs, trees, fruit and potatoes can have a thicker layer. Leave a 5-8 cm (2-3 in) gap round the stems of trees and shrubs when spreading an organic mulch, to prevent rotting.

It is easier to mulch after sowing and planting but, where a mulch is in place, just scrape it aside to reveal the soil and replace it once you finish planting. Mulches are more effective insulators if they are kept loose, so check organic materials after heavy rain and gently loosen any compacted surfaces with a garden fork.

Manure allowed to rot down for at least a year makes a nutritious mulch for spreading generously around fruit, vegetables and roses. Dried and composted manure in bags is expensive and too concentrated for mulching, so is best used as a soil improver.

Garden compost is nourishing and free of charge, but it must be well made or it can introduce persistent weeds to previously clean soil.

Leaf-mold is an excellent soil conditioner. Sieve out the finer material for making potting compost, and use the coarse residue for mulching around any type of plant.

Cocoa shells are a waste material that is light, pleasant to handle and both decorative and natural looking. This mulch may form an impervious surface after heavy rain.

Grass cuttings are a useful mulch around well-established acid-loving plants such as rhododendrons and raspberries. Do not use for several mowings after weedkiller has been applied to the lawn.
straw (6) is spread around strawberries, cucumbers and squashes to ensure clean fruit. It is also useful for keeping greenhouse beds moist and for protecting frost-sensitive perennials in winter.

Sheet Mulches

Black plastic is widely used for mulching strawberries, potatoes and other crops. Lay the plastic over prepared soil and secure the edges by burying them in slits made with a spade, then plant through smaller slits, cut with a sharp knife. Black plastic absorbs heat and excludes light, effectively suppressing weeds, but it is impermeable. It can successfully be used to clear a large area of weedy ground, such as a new vegetable plot if it is left in position for a year or two.

Clear plastic is sometimes spread over the soil to warm it up in early spring or to protect a prepared seedbed until needed.

Black mulching paper is permeable and, like black plastic, used for short-term vegetable crops.

Geotextile membranes are long-lasting materials that suppress weeds while allowing water to penetrate. They are widely used under shredded bark and gravel.

Floating mulches include fleece and thin perforated plastic sheeting. They are spread over plants to help retain heat and moisture. They also protect crops from many flying insect pests as long as the edges are well secured (see black plastic). Since the materials are permeable and very light, they can be laid in position immediately after sowing and will rise with the plants as they grow. Use them in early autumn to protect crops against one or two degrees of frost.