Mulches and mulching

Mulches are an invaluable garden aid. They are used to reduce water usage, to clear ground and to suppress weeds in planted areas. They work in weed suppression by excluding light, without which plants cannot grow. Mulches are applied as a 5-10 cm layer, depending on the material.

Water conservation

Using mulches is one of the easiest methods of water conservation. They keep the soil cool and reduce evaporation. They suppress weeds, which take up large quantities of water. Mulches such as gravel and pebbles also prevent surface run-off.

Clearing ground

Cut down long grass and weeds. Lay the mulching material over the area to be cleared. If weeds come through the material, lay a little more over that area. This method will take at least six months.

Suppressing weeds in planted ground

Apply and incorporate organic matter, e.g. compost, into the area before applying the mulch. Always mulch a warm, moist and weed-free soil. Avoid heaping mulch around plant stems as this can lead to rotting in winter.

Many types of mulch break down into the soil, so re-apply to ensure an effective barrier.

Mulch materials

Black woven plastic

Will let air and water through, so plants can be fed and watered. However, worms cannot work in any organic matter applied to the membrane. Will last for about 15 years when covered with a loose mulch and is useful to stand pots on outside. However, it is expensive and is a non-renewable resource.

Black plastic sheeting

Will last for 1-3 years, depending on thickness. Useful for clearing ground prior to planting and warms up the soil. However it is not advised for long term use as it will not let air and water through and will degrade quickly if not covered. It is also a non-renewable resource.

Cardboard

Flattened boxes are free and will last for a season. Useful for clearing ground and when weeds grow through, they can be easily replenished. In windy areas, will need to be held down by bricks or planks.

Newspaper

Only use black and white newspaper, as colour supplements contain some heavy metals. Excellent for short-term weed suppression. Needs to be held down with a loose mulch such as grass clippings or straw. Useful in the vegetable garden, around the bases of fruit bushes and makes good tree mats. Can acidify soils with a low pH.

Carpet

Only use heavier wool and hessian-backed carpets. Good for paths if covered with bark.

Leaf mould

Excellent mulch as it slowly provides humus and nutrients. It can be slippery on paths but attractive for decorative beds.

Garden compost

Provides nutrients, but it is too valuable to use as a thick layer.

Woodchip

Cheaper than ornamental bark, good for informal paths. Woodchip can cause nitrogen shortage for new plants, so mix a nitrogen-rich organic fertiliser in the mulch to counteract this.

Sawdust

Like woodchips, it can cause nitrogen robbery, so it is best used on paths. Do not use sawdust from treated wood.

Ornamental bark

Made from composted and graded conifer bark. Attractive, so is good for decorative beds. Unlike woodchips, does not cause nitrogen shortage. However, it is expensive and the soil must be weed free before application.

Hay or straw

Should be used over a layer of newspaper for effective weed control. Best to use semi-rotted material so it doesn’t blow away.

Very good for fruit bushes; straw supplies some potash and hay, potash and nitrogen. Hay can introduce weed seeds.

Pebbles, gravel or slate

These be expensive but are excellent for preventing surface run-off and soil compaction. Winter rotting of stems is reduced as soil drainage is improved. Attractive on alpine and scree beds.

Lawn mowings

Excellent for holding moisture in the soil, but avoid any from lawns to which weed killer has been applied. Spread 2-3 days after cutting, to avoid it heating up excessively.

Shredded prunings

Can be used fresh on paths, but compost for a few months before using on a planted area. To reduce risk of spreading disease, do not apply prunings around parent plant. The success of a mulch in the garden depends on choosing the right mulch for the right job.

Flower garden (alpine beds)

• Woven plastic + ornamental bark
• Ornamental bark ·
• eaf mould
• Lawn mowings
• (gravel and pebbles)

Vegetable garden

• Garden compost
• Lawn mowings
• Leaf mould

Fruit garden

• Newspaper + hay or straw
• Garden compost

Paths

• Newspaper
• Carpet + ornamental bark
• Woodchips or sawdust
• Shredded prunings

Land clearance

• Black plastic
• Carpet
• Cardboard