Explainer: How to mulch your garden and why you should

A layer of mulch on the soil confers many benefits. Experienced gardeners know it’s the key to fertile soil and healthy plants.

My garden has a challenging clay soil that takes on a concrete-like consistency in summer, but since I’ve stated mulching like a maniac I’ve witnessed a huge improvement in my soil’s health and now am a fully fledged mulching convert.

What is mulch?

Mulch is a protective layer of material on top of your soil to insulate it from dryness, warm the soil up, add nutrients or suppress weeds. The word mulch comes from the middle English word molsh, meaning soft and moist.

In nature, soil is usually covered by a layer of mulch from decaying matter such as leaf litter or groundcover. In most environments, it’s unnatural for soil to be left exposed to sun and wind and the same goes for your garden beds.

Open, exposed soil always suffers more in summer than soil that’s partly shaded, mulched or even weedy!

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Why mulch at all?

In spring and summer, when plants are growing rapidly and conditions are heating up, it’s particularly important to mulch your garden because it prevents the soil from drying out. It also allows plants to put their roots down deeply so you don’t need to water as often.

Plants that are stressed by a lack of water are less productive and more likely to be mauled by sucking bugs such as aphids and green shield beetles. By acting like an insulating blanket, mulch ensures that moisture levels are consistent, which is important for crops such as tomatoes that are susceptible to conditions like blossom-end rot or develop split skins with too many extremes of wet and dry.

Mulch can also extend the growing season by trapping warmth around crops in the cooler months.

Mulch also suppresses weeds. If you add a good thick layer, say 10cm deep, weeds tend to put their energy into growing long and spindly as they try to reach the light rather than putting down strong roots, which makes them easier to pull out.

Mulch also provides a home for many types of soil life, such as worms, which feed on decaying matter to produce humus, which is like gold dust for your soil because it retains water and makes your soil loose and friable.

What can I use as mulch?

If you want to splurge a little, you can buy commercial mulches such as pea straw and bark-based mulches. They are popular choices and can be bought by the bag from garden centres.

• Pea straw lasts around one season but improves your soil structure as it breaks down.
• Bark lasts three years or longer and also improves the structure of your soil.

If you’re mulching on a budget, use what you’ve got. At my house, we make mulch out of feijoa tree leaves. We leave them to rot down over autumn, then pile them on the garden in spring. We also put the feijoa tree prunings through a mulcher as well.

Lawn clippings

Lawn clippings are an excellent, nitrogen-rich source of mulch, particularly for nitrogen-hungry citrus trees. Just don’t spread them more than a couple of centimetres thick as they can become slippery and stinky.

Weeds and other plants

You can also use weeds as mulch. Just make sure you’ve removed any seedheads first and don’t use invasive weeds such as tradescantia or bulbous weeds such as oxalis. Leave weeds to wilt for a day and then turn them root side up when mulching with them.

You can also use living plants as mulch, such as in the traditional Native American Three Sisters method where beans grow up corn plants and squash grows at the bottom, its large leaves mulching the soil.

Seaweed

This gift of the sea makes a fantastic mulch that is rich in valuable nitrogen, phosphorus and potassium.

Stones and gravel

They don’t add humus to the soil but do lock in moisture, suppress weeds and reduce transfer of soil-borne diseases during rain or watering.

Other options include shredded cardboard, newspaper, sheep dags, and even the pine needles from your Christmas tree.

Compost can be used as a mulch too, although that won’t help you to suppress weeds. Or use your old bean plants, comfrey leaves or cover crops such as mustards and lupins as mulch. To speed things up, use a mulcher.

Where should I put the mulch?

All plants benefit from mulch. Spread it around your trees, shrubs, fruit trees and bushes (particularly those that have been planted in the last year), perennials, bulbs and annuals in the flower garden, and vegetables.

However be careful that the mulch doesn’t smother small plants or touch the trunks of woody ones as this can burn the stems or soften them, making them vulnerable to disease.

Go for a donut shape of mulch around trees. Other plants such as strawberries and lettuces are happy to be tucked up snug as a bug in a rug in their mulch though and, in the case of strawberries, this also keeps their fruit clean.

And the golden rule is also to water well before you mulch or mulch after rain, so you’re not locking dry soil in.

Basically, mulch, mulch and more mulch is what you need. Follow this many layered approach to gardening and your garden will reward you with mulch joy.