Mulching means putting down a nice thick blanket of compost or other material on top of the soil in spring or autumn. It’s great at keeping weeds down. It keeps warmth and moisture in the soil, protecting a plant’s roots and so benefitting the whole plant. It helps to give a lovely open structure to the soil. Mulching is really one of the best things you can do for your garden.

In this post we’ll talk more about what mulch is, its benefits and how to use it.

Kitten on hardwood mulch. Protect. Mulching

Kitten on hardwood mulch. © AnIndianaGirl and reused under the Creative Commons Attribution-Share Alike 3.0 Unported licence.

What is mulch and how to use it

You can make your mulch ‘blanket’ out of anything. Whether it’s organic and biodegradable (for example, garden compost, leaf mould, spent mushroom compost) or not (gravel, carpet, plastic), covering the ground will suppress weeds and keep in moisture. For improved soil structure, though, use organic materials.

Get ready to mulch when the soil is warm and moist. That’s in spring after the frosts have finished and in autumn before the first frosts. Don't mulch cold and wet ground.

Prepare the ground by weeding, dividing and moving plants. Then, when the ground is warm and moist, spread the mulch thickly in the spaces between plants.

  • Leave a small gap around the stems so they don’t rot from contact with wet mulch.
  • Spread mulch in a ring around, not touching, the base of shrubs and trees.
  • Don’t mulch the top of perennial plants.
  • Avoid any annual seedlings, and bulbs too.

In general, a thick layer is better than a thin layer but any layer will improve soil structure. Try to go for a layer at least 5cm / 2 in thick. To suppress weeds you’ll need it to be at least 8-10cm / 3-4in thick.

Mulching keeps weeds down

A thick, dense mulch suppresses weeds because it blocks light and this prevents annual weed seeds from germinating. Lack of light makes perennial weeds (such as dandelion, thistle, bindweed and ground elder) weaker and so they are easier for you to weed out.

Mulch of woodchips at RHS Wisley, Surrey, protects and improves the soil. Miss Marple. Mulching

Mulch of woodchips protecting soil at the Royal Horticultural Society garden at Wisley in Surrey. © Rowan Adams. Licensed for reuse under Creative Commons Licence Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)

A weed-suppressing mulch can be anything that blocks light, so it includes carpet, black plastic, stones and tiles, as well as organic mulch. It’s a great way of keeping a piece of ground weed-free until you’re ready to use it.

Mulching keeps warmth and moisture in the soil

Mulching keeps warmth in the soil. This benefits your plants by protecting their roots from swings in temperature, and from frost! Put down a covering in autumn to keep the summer’s warmth in the soil for as long as possible.

Mulching reduces evaporation so it keeps moisture in the soil and helps you make the most of rain. Anything that covers the soil and also lets rain in will do – gravel, grass clippings, carpet, leaves, pebbles, straw, tiles, bracken. Put down mulch in spring when the soil is moist. This will help your plants through any dry periods. Mulching can mean that you don’t have to water at all.

Organic mulch helps to develop a lovely soil structure

Garden compost. Mulching

Well rotted garden compost loosely spread under raspberry canes. Sarah Buchanan

Organic mulch (such as homemade compost, shredded trees and shrubs, straw, leaf mould, bark chippings, well-rotted farmyard manure and crushed shells) is taken into the soil by earthworm activity. It’s a sure-fire way of developing a good soil structure and also adds to healthy soil's food-web of bacteria, fungi, protozoa and nematodes.

A good soil structure absorbs and holds moisture so roots can find it and take it up easily, but it drains enough so it does not become waterlogged. A good soil structure makes for healthier plants.

Mulching also prevents soil from blowing and washing away in strong winds and storms.

Put down an organic mulch in borders and around fruit and vegetables such as courgettes, strawberries, fruit bushes and asparagus.

Plan ahead now so you're ready to mulch your garden when the frosts are over.