What is a mulch?

It is a gardening term for something which covers the soil, keeps moisture in and – most importantly - prevents weed growth.

Why and where would I use it?

You can use a mulch to clear a patch of weeds, to keep your soil moist, and even to create a path. Some mulches will also feed the soil, giving the plants nutrients. In fact mulches are a labour saving trick which all organic gardeners can use.

Here are three different types of mulch:

  1. Grass cuttings - often used to keep soil moisture locked in round bushes and plants. As the cuttings rot down they will release nitrates into the soil.
  2. Bark and shreddings - used to create paths and suppress weeds.
  3. Cardboard, newspaper or plastic membranes - used to prevent light on the soil, thereby stopping weeds from growing.

So how do I put down a mulch? And when?

This depends on where you are using a mulch.

In beds that are already planted, make sure your mulch goes down onto warm, wet soil. If the soil is cold and dry it will stay that way, hampering plant growth. The easiest stuff to use here is grass cuttings. Put a thick layer around the plants, having watered the soil first if necessary. Take care not to go right up to the stems - leave a ring of at least 10-15cms clear soil.

If you want to clear a patch of weeds – and this is especially good for anyone taking on a new allotment – then your mulch needs to be more robust to prevent light reaching the soil. A plastic membrane or thick layers of flat cardboard are ideal (don’t use carpet, the dyes - which may be toxic - can leach out into the soil.)

First cut the top growth off the weeds and either leave them on the soil, or throw them on the compost heap. Then cover the whole area with the cardboard or membrane and make sure it is fixed in place. If you add compost, straw or manure under the membrane, then the soil microbes and worms will break it down into the earth, giving the soil a lovely crumbly texture when you take the mulch off. This helps if you have to pull out the most persistent weed root systems such as bindweed and dock.

Now all you have to do is to leave it for 6 to 12 months. Without light and moisture the weeds won’t survive.

And finally, you can use bark and woody shreddings as a mulch to create a path. Lay them thickly (at least 15-20 cms thick.) It up to you if you want to use a membrane underneath - this gives double protection against weeds coming through, but if often looks unsightly as the bark wears away.

Finally - thick mulches of manure or compost can be used as part of the No Dig technique.