Mulching your garden: how and why to mulch

17 June 2021

Find out how mulching your garden can prevent weeds growing and improve your soil at the same time.



If you want to spend your summer relaxing in the garden, rather than weeding and watering, try mulching beds and borders - a thick layer of leafmould, composted bark or other covering material, will make maintaining borders easy and give your plants a boost at the same time.

Why mulch?

There are many reasons why mulching the soil every year is a good idea.

Suppress weeds 

A deep mulch will prevent weeds from growing, which rob moisture from the soil and need constant hoeing or pulling out by hand to control. Although some weed seeds will germinate on top of the mulch, they cannot anchor themselves well in the bulky material and are easy to uproot.

Feed the soil

Although winter rain can wash goodness out of the soil, you can give it a pick-me-up by spreading mulch, because as the material rots down nutrients are released back into the earth, improving the soil in the process.

Lock-in moisture 

If applied over wet ground in the spring, it will also help to lock in moisture that can be used by plants in warmer weather. This is a real boon given recent water shortages and the threat of hosepipe bans in some parts of the country.

Protect tender plants

Mulches can also be spread over tender bulbs or around the stems of less hardy plants in winter to help insulate them from frost.

Which is the best mulch?

If you have made your own leafmould or garden compost this is ideal for mulching, but don't worry if you haven't. Garden centres and DIY stores stock a large range of materials that can be used instead, including well-rotted farmyard manure, composted bark and organic wheat straw. If you have a local brewery you might even be able to get spent hops for free, but be warned hops are toxic to dogs so do not use them in your garden if you have a dog or dogs visit as it can prove fatal.

Choose a mulch that will suit your garden - wheat straw sets off tropical plants wonderfully, but looks out of place in a traditional border. Probably the most popular material is bark, which is available in several grades. As a rule of thumb: the finer the grade, the quicker it will rot down and need replacing.

In some gardens gravel or slate shingle makes an attractive mulch - lay it on top of a sheet of landscaping fabric (available from garden centres) to prevent it from being trodden into the soil, but obviously slate and gravel won't feed the soil.

Sheet mulches can also be used, although they're unattractive so are more likely to be seen at an allotment or covered in a decorative mulch such as slate or gravel. Many allotmenteers use sheets of corrugated cardboard weighted down with stones, although it's impossible to know what chemicals recycled or treated cardboard might contain.

Find out how to make a compost heap

How to mulch the garden

Before laying a mulch, clear the site of weeds and make sure the soil is moist. 

If necessary, soak well as it will be difficult to wet the soil after it has been laid.

Spread a 10cm (4in) layer of mulch material across the whole area with a spade and rake to leave a level finish - wear gloves if you are handling manure or composted straw. 

Avoid the mulch touching the stem of the plant as this can make the stems too soft, leaving them vulnerable.

Although the mulch will help to conserve moisture, you will have to apply water during prolonged spells of dry weather.

When to mulch the garden

Spring is an ideal time to mulch, but if you left it too long it can be done any time, as long as the soil is moist. 

My mulch is moldy, can I still use it?

It's not uncommon to see some biodegradable mulch, especially bark, coated in a powdery white fungal growth. This is likely to be a saprophytic fungi, a harmless fungi that feeds on decaying matter, breaking it down into nutrients that then feed the plants. It might not look attractive but it does not harm living plants.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.