Mulches are loose coverings or sheets of material placed on the surface of soil. Mulches can be applied to bare soil or to cover the surface of

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

Depending on the type of

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings.

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings.

mulching

• Help soils retain moisture
• Reduce watering
• Suppress weeds
• Improve soil organic matter
• Provide nutrients
• Deter some pests
• Warm up soil in spring
• Protect plant roots from extreme hot and cold temperatures
• Encourage beneficial soil organisms
• Provide a barrier for edible crops coming into contact with soil
• Give a decorative finish

Mulches can be split into two main groups;

Anything that can be decomposed by fungi, bacteria and micro-organisms, so it doesn’t persist indefinitely in the environment. Biodegradable plastics are usually made from plants, such as bamboo, rather than fossil fuels. Ideally, products that claim to be biodegradable should break down quickly and leave nothing harmful behind. However, they may need specific conditions in order to biodegrade successfully or may produce greenhouse gases such as methane in the process.

Biodegradable mulches

These break down gradually to release

To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key plant nutrients usually derived from soil are nitrogen, phosphorus and potassium, while carbon, oxygen and hydrogen are absorbed from the air. Other vital soil nutrients include magnesium, calcium and sulphur. Gardeners can add nutrients by applying fertilisers (either artificial or naturally derived) to boost plant growth and improve flowering and fruiting.

Non-biodegradable

Non-biodegradable mulches do not boost the fertility or structure of the soil, but they do suppress weeds, conserve moisture and some have the added advantage of looking decorative. Slate, shingle, pebbles, gravel, stone chippings and other decorative aggregates are often used as a mulch across beds. Sea shells, tumbled glass and similar materials can be used on the surface of containers, but it is best not to use any materials made from plastic. Dark coloured material will warm the soil in the sun whereas light coloured mulch such as white gravel will reflect sunlight and keep roots cooler in strong sunlight.

Sheet mulches or woven landscape fabric can be used for new beds or borders. After laying, slits can be made in the fabric, allowing direct planting through it. The downside is these mulches do not look very attractive, but they can be camouflaged with gravel, bark or others materials. To allow rain and irrigation water to reach the roots always choose a permeable sheet as a waterproof layer may cause surface runoff and drainage problems elsewhere. 

Mulches are best applied from mid- to late spring, when annual weeds have not yet germinated and herbaceous plants are dormant, and autumn, as plants are dying back. They can be applied around new plantings or to established beds and specimen plants. New plants that need to establish can be mulched at any time of the year when they will benefit from weed suppression and moisture retention in the soil. 

Beds and borders can be mulched entirely, taking care not to smother low growing plants or to pile mulches up against the stems of woody plants.

• To be effective, biodegradable mulches need to be between at least 5cm (2in) and ideally 7.5cm (3in) thick
• Lay mulches over moist soil, after removing weeds, when the soil is not frozen
• When creating new beds, planting through mulch sheets is effective
• Single trees and specimen shrubs are best mulched to the radius of the canopy
• As it decomposes over time, a biodegradable mulch will feed your plants and microorganisms in the soil reducing the need for additional soluble feed
• Ground covering mediterranean plants such as Thymus species may be best left unmulched as it can hold too much moisture around the stems and foliage

If laid correctly there is generally no problem with mulches. However, if they are in direct contact with the stems of trees or specimen shrubs they can cause the stem to soften, making it vulnerable to diseases.

To save water and suppress weeds, the type of organic material you choose is less important than putting on a thick enough layer. Thicker layers will block sunlight from weeds, insulate the soil better and reduce the amount of water evaporating.

Depending on the quality of the material there is a possibility of introducing weeds, pests and diseases to the garden and, with woodchips there is a slight risk of introducing honey fungus.

Once you have added a mulch to the soil you may need to apply extra water to reach the roots of the plants beneath, but mulch will also help rain to soak into the soil, and less water will evaporate, so you should find you need to water less frequently.

Using freshly chipped material such as woody prunings or grass clippings can encourage the microorganisms in the soil to grow but they may use up reserves of nitrogen, leaving less available for plant growth. If you have freshly chipped material, keep it stored for a few weeks before using.

There is no need to remove mulches to apply fertilisers. Fertilisers are spread over mulches in late winter and are washed down to plant roots by rain.

Avoid damaging roots of plants by hoeing weeds growing in mulches around permanent plants. Remove weeds by hand and add a further layer of fresh mulch.

Organic mulches can be easier to maintain as they can be replaced by adding another layer when it has completely rotted away. Gravel can sometimes mix with the underlying soil if not applied thickly, encouraging surface weeds. 

It is not uncommon for the white fungal mycelium of harmless saprophytic fungi to be found in soil that has been covered or enriched with an organic mulch. This is nothing to worry about and there is no need to dig out the mulch or white fungal growth.