8 things you should know about mulch

With the approach of winter, gardeners everywhere will soon be into mulching. But do you know how to properly add mulch to your garden? Here are eight important things you should know about mulch to help protect your garden over winter, so it has a good start next season.

Mulches have three main functions: they regulate soil temperature, reduce water loss and help with weed control. What's more, they may be organic, inorganic or a combination of both. Are you adding mulch to your garden properly to give it the best chance of flourishing next spring?

Sheets of plastic laid on the soil in early spring will warm the soil quickly and enable it to dry out faster. They can be used to prepare a site for an early crop of lettuce, or to warm the soil for sowing melon seeds.

• Black plastic has the advantage that it smothers any weed seedlings that germinate beneath it and can be used to control perennial weeds.

Loose mulches laid between the plants or around trees and shrubs help insulate the soil from extremes of temperature – but they also work in reverse and hold high or low temperatures in the soil. This is important where winters are cold.

• Don't pack down mulch too tightly. Otherwise, it loses any "insulating" properties it affords the soil.

Trees planted in fall should not be mulched until the following summer.

• A mulch applied at planting time will keep the soil frozen until late spring, which could harm the young tree. That's because their foliage – in warm air – starts to grow before the soil thaws and the roots can't take up enough moisture (the roots only extend as far as the mulch), which often kills the tree.

Where winters alternate between freeze and thaw, heaving can be a problem.

• A loose mulch applied in early winter after the soil has cooled, or even frozen, will help to prevent this.

By protecting the surface of the soil from the sun, wind and heat, loose mulches can help to significantly reduce water evaporation.

• Mulch also helps to reflect the sun's heat, further reducing the need for watering under the drought conditions.

If applied 10 to 15 centimetres (four to six inches) deep, a good layer of mulch can cut off the light to weed seeds.

• If laid around trees and shrubs, the mulch should not be put too close to the trunk. As well, the mulch layer should extend only to the end of the trees' and shrubs' branches, otherwise you may be overdoing it.

Organic mulches should be large enough to resist being blown or washed away, but must allow the passage of water and air.

• Coarse bark chips and shredded cedar bark are the most commonly available, but cocoa husks or spent hops are also good mulches.

If you restrict air circulation to the plant's roots and the soil is too damp, there's a chance they could begin to rot – which could potentially spell trouble for the plant's overall health.

In addition to plastic sheeting, landscape fabric (also called geotextile cloth) can be used as an inorganic mulch.

• Although it allows water to pass through and stops weeds from growing, landscape fabric will break down in sunlight and has to be covered with a thin layer of organic mulch.