Mulch is a thick layer of material placed over the soil and around plants, used to suppress weeds and lock moisture into the soil, while acting as a physical barrier to drying winds and direct sun. Some mulches also contain nutrients, acting as slow-release plant food. As worms take the mulch into the soil they help to improve soil structure, making it more moisture retentive, free-draining and fertile.
Organic mulches also contain nutrients, acting as slow-release plant food. What’s more, while they’re breaking down they attract beetles, worms and other soil invertebrates, which provides food for birds.
Mulching: jump links
- Types of mulch
- When to use mulch
- How to apply mulch
- Where to apply mulch
- How to make mulch
- Problems with mulching
Find out more about mulches and mulching, in our guide, below.
Types of mulch
There’s a wide variety of mulches to use – both organic and inorganic – which have different uses in the garden. Organic mulches are made from dead plant material such as compost, leaves, bark or grass clippings. Inorganic mulches include rocks or gravel but they can also include plastic sheeting, landscape fabric and ‘rubber mulch’. Unlike organic mulches, inorganic mulches do not break down. Indeed some, such as plastic sheeting, can disintegrate over the years and pollute your garden environment. Inorganic mulches don’t add nutrients to the soil and can, in some instances, stop nutrients reaching soils. However they can offer a more long-term solution to weed suppression than organic mulches.
Organic mulches include:
Leaf mould – low in nutrients but an excellent soil conditioner, leaf mould provides a quick reward for a little effort. Simply bag up leaves in autumn and they should be ready to mulch around your plants after around 12 months.
Well-rotted horse manure – this is packed with nutrients and retains moisture well. It’s excellent for mulching around hungry plants like roses and edibles, especially pumpkins and squashes. Make sure it’s been left to rot for at least two years, otherwise it can ‘scorch’ plant leaves and even remove nutrients from the soil as it breaks down.
Homemade garden compost – this is is a fantastic all-round mulch, great for retaining moisture, suppressing weeds and improving soil. Add kitchen scraps and chopped up garden waste to your compost bin and turn every few months. You should have a useable compost between six and 12 months later.
Composted woodchips or bark – this bulky mulch breaks down slowly and is ideal for improving soil structure by improving drainage and making it more moisture retentive. Also, its dark colour makes offsets the green of plants beautifully.
Mushroom compost – often bought as ‘spent’ mushroom compost, this alkaline mulch is light and easy to use. Given its high pH, it’s ideal for lime-loving vegetables, including brassicas like kale, cabbages and broccoli. Avoid using on lime-hating, ericaceous plants like rhododendrons, camellias and heathers.
Want to know more about organic mulch? Watch our No Fuss video guide, where David Hurrion reveals some of the basic forms of organic matter, including rotted horse manure and home-made compost, and explains where they’re best used:
Inorganic mulches include:
Rocks or gravel – rock or gravel mulches are typically used in gravel gardens, and can help seal moisture into the soil and suppress weeds. Bear in mind that rock or gravel mulches can heat up in the sun and cause the planting area to become too hot for many plants to grow. They’re best used in drought-resistant planting schemes.
Plastic sheeting or landscape fabric – this is laid over the soil and suppresses weeds. Some fabrics are better than others. Bear in mind that some will disintegrate over time and leach plastic fragments into the soil and surrounding environment. It’s also thought that impermeable sheeting also stops rain, air or nutrients reaching the soil, which makes it a bad option for using around plants, which need water, nutrients and air to live.
Rubber mulch – made from recycled tires, rubber mulch can suppress weeds and breaks down naturally, albeit very slowly. However, it’s not clear how toxic rubber mulches are. Potentially material from old tyres could contain a number of harmful chemicals from the road that could leach into your soil.
When to use mulch
The best time of year to mulch is spring and autumn, although April is the ideal time to mulch with organic compost as the soil is moist and accessible, and plants are just starting into growth.
How to apply mulch
Applying compost is easy – simply lay 5cm of your chosen mulch onto the bed or around key plants, without smothering them or damaging the lower stems. Bear in mind that a really thick layer of mulch will suppress more weeds, but bulbs and other plants will find it hard to grow through more than a 5cm layer. Use your hands or a spade to add the mulch, depending on the material you choose. Finally, use a rake or hoe to make sure the mulch is evenly distributed.
When applying mulch, it pays to prepare the soil beforehand. This will save you time and effort in the long run:
- Fork out perennial weeds and pull out annuals by hand
- Rake the surface of the soil to level out dips and hollows, then re-firm as necessary
- Water thoroughly to ensure the soil is moist before applying the mulch, so the mulch keeps the water in the soil
Where to apply mulch
Around spring bulbs – mulching around spring bulbs as the foliage dies back will feed the bulbs and lock in moisture just when they need it. Mulching will also reduce the need for digging, which can easily lead to bulb damage.
Under hedges – apart from regular clipping, hedges are often ignored. Their roots are packed together, and benefit from an annual mulch to lock in moisture and feed the plants. Make sure the soil is moist or water well before mulching.
Around herbaceous perennials – dark organic mulch visually sets off herbaceous perennials. If you’ve just divided and watered them, then mulching around the new plants will give them a boost as the growing season gets going.
Around fruit trees and bushes – fruit trees and bushes need plenty of moisture around their roots, especially when fruit is forming. A regular mulch will suppress weeds and help keep the plants healthy and resistant to pests and diseases.
How to make mulch
You can make your own mulch by composting kitchen and garden waste. You can also make your own leaf mould. If you have access to a local stables you can buy (or be given) horse manure which you can pile up to rot down (make sure all animal manure has rotted down for at least two years otherwise it may scorch your plants).
Problems with mulching
Problems with mulching occur usually when you’ve mulched too thickly, which prevents bulbs and herbaceous plants from growing. Gently use a rake or long-handled cultivator to gently thin out the mulch, which may help plants grow better.
Here, Kevin Smith, BBC Gardeners’ World Magazine, explains which bulbs grow through mulch and how deeply to mulch your soil:
Another problem you might experience is when using manure to mulch plants. If this isn’t well-rotted it can scorch plant leaves and even lead to the, becoming distorted.
Some types of inorganic mulch can disintegrate into the soil, heat up the planting area and potentially leach harmful chemicals into the soil.