Mulching to Improve Garden Soil


Mulching means covering the ground with a layer of material. Mulches can either be biodegradable (generally loose organic materials such as compost, manure, leafmould and bark, which will eventually rot down) or nondegradable (sheet materials such as plastic, which do not add organic matter to the soil). Both types of mulch help to control weeds, and this is the most important use of nondegradable mulches and other sheet mulches such as newspaper.

Mulching to Improve Garden Soil

Mulches help retain moisture in the soil, in particular the top several centimetres, which is beneficial to shallow-rooted plants. They also protect the soil surface from pounding rain and can keep crops clean and free from disease. They can also alter the temperature of the soil and the air just above them. Dark mulches absorb heat in the day and radiate it at night, while light-coloured mulches reflect heat rather than store it. The temperature above light mulches can thus be significantly lower at night.

Biodegradable mulches

It is biodegradable mulches that play the most important part in soil management. Organic matter is added to the soil as the mulch is taken under by worms and other soil-living creatures and gradually broken down. This improves the soil structure and supplies plant nutrients. The quantity and rate at which the nutrients become available depends on the particular mulch. Even stemmy materials such as straw, which would normally induce nitrogen robbery, can be used as a mulch if dug into the soil; the small amounts taken under gradually by soil organisms do not usually cause problems. However, only use such mulches around permanent plantings or where they can be removed easily at the end of the season so you do not accidentally incorporate them into the soil.

Applying a loose mulch

It is essential that the soil is wet before you apply a mulch, since rainwater will only percolate slowly through the mulching material and some will be absorbed before it reaches the soil. It is also vital that the soil is warm, since the mulch can act as an insulating barrier and prevent the soil from warming up quickly. This is particularly the case with light-coloured mulches. Never apply such a mulch in winter or early spring.

However, once in place on a warm moist soil, the mulch helps to keep it warm and moist but prevents it getting too hot or wet. This moderating effect is very beneficial to soil life and plant roots.

Spread the mulch evenly over the soil surface. How thick you apply it will depend on the size of the plants and how much material you have available. Even a 1cm (3/8in) layer will help to improve the soil structure, but it takes 7.5-10cm (3-4in) of a loose mulch to control weeds effectively.

In most cases you should keep the mulch a few centimetres away from the plant stems as it can encourage rotting and cause a grafted tree or shrub to shootfrom the rootstock. However, occasionally mulching right round the stem can be beneficial. Tomatoes and brassicas, for example, will make new roots into a mulch and this helps them to grow.

Slugs and Mulches

Rapidly decaying mulches, such as compost, grass mowings and hay, provide the moist, nutrient-rich environment that slugs love. However, some argue that the mulch provides an alternative food source for slugs and encourages slug predators such as ground beetles, so less damage is done to plants. A dry mulch such as bark or shredded prunings is less likely to encourage slugs, and cocoa shell is said to deter them.






On seedbeds

Around bedding plants, herbs, herbaceous plants

In autumn before sowing

Any time when soil conditions are suitable

To improve soil structure

To improve soil structure and moisture and look attractive


On vegetable crops with a long growing period

Around herbaceous plants

When well-established and still actively growing

In spring

To provide nutrients and keep in moisture

To provide nutrients, keep in moisture and improve soil structure

Worm Compost

On plants in pots or individual garden plants that need feeding

Any time when growing strongly

To provide nutrients

Well-Rotted Manure

Around plants that need a lot of feeding

When making quick growth, usually in spring

To provide nutrients, particularly nitrogen

Lawn Mowings

Around widely spaced vegetable crops

Any time when soil conditions are suitable

To control weeds and keep in moisture

Shredded Prunings

Around trees and shrubs.

On paths.

Any time when soil conditions are suitable

Any time

To protect soil surface and control weeds

To keep the surface clean


Around trees and shrubs

Any time when soil conditions are suitable

To protect soil surface, look nice and control weeds


Around fruit on the ground

Between widely spaced shrubs, fruit trees and bushes

On paths

Before fruit forms

Any time when soil conditions are suitable

Any time

To keep fruit clean and keep in moisture

To control weeds and keep in moisture

To keep surface clean


Around fruit trees, canes and bushes

In late spring

To control weeds, provide nutrients and keep in moisture

Cocoa Shell

Around bedding and herbaceous plants

When in active growth

To control weeds, look attractive and provide nutrients

Sawdust/ Woodshavings

On paths

Any time

To keep surface clean

28. January 2011 by Dave Pinkney
Categories: Manures and Fertilisers, Soil Cultivation | Tags: , | Comments Off on Mulching to Improve Garden Soil


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