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There are several benefits that come with mulching. The primary is the way it suppresses weed growth, thanks to its blanketing effect – most weeds can’t push through the mulch layer and those that do make it are weak and can be easily removed by hand. In addition, weed seeds can’t get through to the soil to germinate.
Mulches also have a beneficial effect on soil temperatures by reducing the wide fluctuations that occur at surface level, from baking hot during the day to cold at night. This means less stress for the plant roots, too. And a healthy garden is all about healthy roots – they’re the powerhouses of your plants!
Types of mulch
There’s a range of materials you can use as garden mulches, but they fall into two main camps – organic and inorganic. Organic mulches are derived from plant-based materials, such as straw, shredded timber and bark. Over time they’ll break down, which has the effect of improving the soil’s structure and water-holding capacity. It also means, of course, that you need to top it up periodically with a fresh layer.
Inorganic mulches are mainly rock-derived – things like pebbles, gravels and scoria. There are also more showy materials available, like coloured crushed glass products, but these aren’t all that practical for covering large garden areas. Because of the lack of soil‑enhancing benefits, it’s best to restrict your use of inorganic mulches to small‑scale decorative uses, such as around pot plants or on small garden beds for colour and interest. Here, you can scrape it back when you need to feed the plant or top up the potting mix.
How deep?
With mulch, there’s a ‘just right’ quantity. Too shallow, and it won’t do its job; too deep, and water can’t get through to reach the soil. As a rule of thumb, spread a covering 2–5cm thick, using the higher level for coarse mulches such as chunky barks and wood waste products. Keep finer mulches like shredded straw to about 2–3cm, as thicker layers can pack down and become a water-repelling blanket – the opposite of what you want.
Compost
Free if you make it yourself, compost also feeds the soil as it breaks down. Use coarse-textured types.
Fallen leaves
Shred up the foliage of deciduous trees in autumn and compost them in bins or large garbage bags. Works best when mixed 50:50 with compost.
Bark
Available in a range of sizes, from chunky to quite fine, bark is a long-lasting mulch. It’s best used around shrubs and trees and for covering large garden areas.
Grass clippings
A free source of mulch, if you mow your lawn regularly. Clippings should be composted for 2–3 months before you use them.
Shredded wood
These mulches are available in a variety of sizes and colours. As they can draw nitrogen out of the soil, spread a layer of manure over the ground before you apply them.
Straw mulch
Derived from sources such as lucerne and sugar cane, they’re lightweight, easy to spread and come in bags or bales. Lucerne also releases nitrogen as it breaks down.
