Understanding Mulch

Never underestimate important role that mulching plays in your garden.

What Is Mulch?

‘Mulch’ is described in The Royal Horticultural Dictionary of Gardening as a layer of material spread on the soil above the roots of plants with the object of (1) supplying ‘food’ to the plant, (2) conserving soil moisture, or (3) preventing sudden fluctuations in temperature.

Understanding Mulch

There are few things as beautiful as watching the seasons change, especially during autumn. Leaves decorate our gardens with their copper-red splendour, swirling to the ground and forming lush tapestries of coloured patches.

This is a gift from the trees at a time, when our lawns receive their last cut and the gardens slowly go to sleep. The last summer veggies get pulled out and surpluses get chopped up, frozen or pickled. But for some gardeners, this is the busy season as they prepare for the colder months. This includes applying that all-important layer of mulch.

That’s a broad if accurate definition, but it’s important to remember that not all mulches are equal. Mulch can be placed in two categories: organic (all previously living materials, like leaves, straw, hay, grass clippings and bark) and inorganic (gravel, pebbles, stones, landscape fabric and plastic). Some have a specific purpose and are better suited in some areas of the garden than others. Organic mulches are better suited to the planted garden if applied correctly, feeding both the soil and microorganisms. Inorganic mulches perform a more decorative role and add no nutritional value to your soil, despite being potentially costly. These are better suited for pathways and seating areas or for demarcating borders and focal points.

Organic Mulches

These mulches break down over time and improve the soil structure. This is why they should be refreshed and added to regularly as soon as you see bare soil. As they break down they release nutrients that feed the soil, soil microorganisms and plants. But they also assist in suppressing weeds, saving water and regulating soil temperatures. This keeps plant roots cool in hot months and warm in cooler months.

Young plants benefit from this consistent growing environment. It means they don’t have to compete with weeds for nutrient uptake in the growing phase, or get stressed from fluctuating soil temperatures. Never apply mulch up to the stems of plants as this can cause rot and disease. Always leave a 2cm gap between the mulch and the plant’s stem.

Some organic mulches have earned a bad reputation in the past, with the worry being that they can alter the soil pH or even add toxins to your soil. It’s an unfair reputation though. Unless you have recently treated your lawn with a herbicide, grass clippings are the cheapest option to use in any garden bed. Just think of all the fertiliser trapped in those blades of grass!

The top third of any lawn is very dense in nutrient value, and grass clippings can be added green or left to dry before being used as a mulch. A layer of 2cm is sufficient. This still allows enough air and water to permeate through to the lower soil. While it is true that grass clippings added too thick can become a breeding ground for fungal diseases, they will never rob your soil of nutrients. Grass clippings are one of the cheapest forms of mulch and are very effective if applied correctly.

Leaves

Leaves are often raked up and disposed of, which is such a waste. They have formed the basis of earth’s soil over millions of years! Leaves feed microbes, which in turn release beneficial trace elements that the trees have stored in the leaves. This makes them available to our plants. Leaves also feed earthworms, which are all important in creating good soil humus and amending soil by lightening clay soil and helping to retain moisture in sandy soils.

Before applying leaves as a mulch, it is a good idea is to shred them. This creates a bigger surface area for the microbes to get to work on and maximises water and airflow to the soil. The smaller particles will break down more quickly, so always have leaves readily available to top up the mulch.

Leaf mould is also an easy way of adding much-needed nutrients to the garden. To make it, place wet leaves in a refuse bag, where they will break down over just weeks and can then be added as mulch to beds. When adding leaf mould to the garden, add a layer of grass clippings or shredded leaves on top. This creates a layered mulch effect. This will prevent the leaf mould from drying out quickly on hot days and so will protect the soil’s microorganisms. So, while the season is raining leaves, use them wisely and allow them to enrich your soil.

Straw And Hay

Straw and hay are two different organic mulches, although gardeners sometimes categorise them together. The discarded by-product of a harvested crop like wheat: the seed heads are removed and the stalks are known as straw. Hay, on the other hand, is usually varying size bundles of grasses, usually used as a feed for livestock. Yes, you guessed it: with hay can come seeds just waiting to germinate. Straw has the benefits of better insulation, as the hollow stems trap heat. And although they do break down over time, the nutrient value is less than that of leaves, lawn and hay. Straw is mainly fibre, and all the good plant’s energy has gone into producing the seed head. Regardless of this, straw adds a beautiful golden hue to any veg garden, making us long for farm life.

Hay has the benefit of being the whole plant, adding nutrients as it breaks down rather quickly. Hay also has the advantage of packing down on the soil, preventing erosion in heavy rains. It is, however, a warm and snug place for snails to hide and should be inspected regularly.

Bark Chips

The last popular organic mulch on our list is bark chips, which shouldn’t be confused with wood chips or wood mulch. These come in different sizes and take the longest to compost or decompose. Depending on the size of the pieces, bark can last up to three years before it needs to be replaced. It is excellent at suppressing weeds when added in a thick layer, as well as insulating the soil during frost periods. But the drawback is that more watering is needed to penetrate the thick layer to get to the soil. Bark chips are a great option for decorative spaces, pathways in veggie gardens, and for use in mature garden beds. It is a costly mulch, so be sure to use it where it will be of most value.

Inorganic Mulches

These are classified as anything not previously living, which means gravel, stones, pebbles and landscaping fabrics or plastics.

Despite not breaking down and adding anything to the soil, they do have a role to play in the garden. This group of mulches are better used as decorative elements, in pathways and high traffic areas. When using gravel, stone and pebbles, they should be placed on landscaping fabric. This prevents your expensive decorative mulch from disappearing into the muddy soil. Landscaping fabric allows air and water to penetrate the soil while suppressing weed growth.

There are also semi-organic mulches that we need to make mention of, such as newspaper and cardboard. These can be used to suppress weeds and will eventually break down and add organic matter to the soil. They are often used as the base for layered or lasagne gardening.

There are many mulches to consider, each with a specific function. And they can be used by themselves or in a combination. You can layer different mulches, and use different mulches at different times of the year or for specific tasks. You can also chop and change depending on what you have at hand at the time. The most important thing is to make sure you are mulching in some way. Start today by giving back to your garden and it will reward you in healthy plants for your plate.

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