Mulch is the single most useful thing most gardeners can do for their soil. A good layer of mulch keeps moisture in the ground, suppresses weeds, moderates soil temperature, feeds soil life as it breaks down, and makes beds look cared for. Yet many gardeners either skip mulching entirely or use the wrong material in the wrong place. The choice matters: a mulch that is perfect for a shrub border can smother a vegetable bed, and a mulch that suits a path can rob a flower bed of nitrogen.
This guide compares the main mulch types, explains what each one does best, and covers the application rules that apply to all of them.
What mulch does
Mulch works in several ways at once. It shades the soil, so less water evaporates and the soil stays cooler in summer and warmer in winter. It blocks light, so weed seeds cannot germinate. It breaks the impact of rain, so soil does not compact or splash onto leaves. And organic mulches — the ones that rot down — feed earthworms and microbes, which in turn improve soil structure and fertility.
A mulched bed needs less watering, less weeding and less feeding than a bare bed. That is why experienced gardeners mulch everything they can. The only beds that are usually left bare are seed beds, where mulch would block germination, and the immediate area around plant stems, where mulch piled against the stem can cause rot.
Organic mulches
Organic mulches are made from once-living material. They break down over time, adding organic matter to the soil — which is their great advantage — but they need topping up, usually once or twice a year.
Wood chip mulch is made from chipped branches and bark. It lasts a long time, looks tidy, and is excellent for paths, shrub borders and around trees. It is not ideal for annual vegetable beds, because it is slow to break down and can tie up nitrogen at the soil surface if mixed into the soil. See our detailed guide to wood chip mulch.
Straw mulch is the classic vegetable garden mulch: light, cheap, easy to spread and quick to break down. It is excellent for mulching vegetables, for strawberries and for keeping soil off low-growing crops. It can contain weed seeds if it is hay rather than straw, so buy straw, not hay. See our guide to straw mulch.
Leaf mulch is free, abundant every autumn, and one of the best soil builders available. Shredded leaves break down into leaf mould, which holds moisture and feeds soil life. Whole leaves can mat together and repel water, so shred them first if you can. See our guide to leaf mulch.
Compost is the finest mulch of all for feeding the soil, though it is usually used in thinner layers than other mulches and is best reserved for beds that need feeding as well as covering. A 2–3 cm layer of garden compost over a bed in spring or autumn is one of the best things you can do for it.
Grass clippings are free and nitrogen-rich, but they must be used thinly — a few centimetres at most — or they mat together, go slimy and smell. Never use clippings from a lawn treated with weedkiller unless the product label says it is safe for garden use. Let clippings dry for a day before spreading them.
Bark mulch is decorative, long-lasting and good for shrub borders and around trees. Like wood chip, it is slow to break down and best kept out of annual beds. Fine bark is better for smaller plants; coarse bark suits large shrubs and trees.
Inorganic mulches
Inorganic mulches do not break down, so they do not feed the soil — but they also do not need replacing, and they have uses where organic mulches struggle.
Gravel and stone are excellent for Mediterranean and drought-tolerant planting, for paths and for areas where you want a permanent, weed-suppressing cover. They warm the soil, which suits heat-loving plants, but they can overheat the roots of plants that prefer cool soil. They are heavy, hard to move and difficult to remove if you change your mind.
Landscape fabric and weed membrane suppress weeds under gravel or bark, but they also block organic matter from reaching the soil and can make the soil beneath them lifeless over time. They are best used under paths and gravel areas, not under planting. Avoid plastic sheeting as a mulch in beds — it stops water and air reaching the soil.
Slate and crushed shell are decorative options for pots and small areas. They look good, suppress weeds and do not blow away, but they add nothing to the soil and can be expensive over a large area.
How deep should mulch be?
Depth depends on the material. For most organic mulches — wood chip, bark, straw and shredded leaves — a layer of 5–8 cm is the standard range. Thinner than that, weeds push through and moisture evaporates. Thicker than about 10 cm, you risk smothering the soil, keeping it too wet in winter and too cool in spring, and creating a home for slugs.
Compost is the exception: apply it in a thinner layer, about 2–3 cm, because it is dense and rich. Grass clippings should be no more than 2–3 cm at a time. Gravel needs about 5 cm to suppress weeds effectively.
Always keep mulch a few centimetres away from plant stems and tree trunks. Mulch piled against a stem — the "mulch volcano" — holds moisture against the bark, invites rot and gives pests and diseases a way in. Leave a clear gap around every stem.
Our mulch calculator can work out how much mulch you need for a bed of any size, so you can order the right amount.
When to mulch
The two main mulching seasons are spring and autumn. In spring, mulch after the soil has warmed up and after you have weeded and watered the bed — mulching cold, dry soil locks in the cold and the dryness. In autumn, mulch after the first rains, when the soil is moist, to protect roots over winter and feed the soil as the mulch breaks down.
Never mulch a dry bed. Water thoroughly first, or wait for rain. Mulch on dry soil acts like a roof, keeping rain off the soil below and leaving plants thirstier than before. This is one of the commonest mulching mistakes, and one of the easiest to avoid.
Do not mulch over weeds. Pull or hoe them first, because a thick mulch will suppress small weed seedlings but will not kill established weeds — they will simply push through. And do not mulch a seed bed until the seedlings are up and big enough to cope; mulch blocks the light that seeds need to germinate.
Choosing the right mulch for the job
For vegetable beds, choose a mulch that breaks down quickly and feeds the soil: straw, compost or shredded leaves. For shrub borders and trees, choose something long-lasting: wood chip or bark. For paths, use wood chip or gravel. For pots, use fine bark, gravel or compost. For strawberries and other low crops, straw is the traditional choice because it keeps fruit clean and dry.
Think about what you want the mulch to do. If the priority is feeding the soil, choose compost or leaf mould. If the priority is weed suppression for a year with no attention, choose wood chip or bark. If the priority is keeping the soil cool and moist through summer, any thick organic mulch will do. If you are unsure, check your local extension service for mulches that suit your soil and climate.
Common mulching mistakes
The biggest mistake is the mulch volcano — piling mulch against stems and trunks. Keep a gap. The second is mulching dry soil, which locks drought in. The third is using fresh, uncomposted wood chip in a vegetable bed, where it can tie up nitrogen at the surface and slow growth. The fourth is using hay instead of straw, which introduces a crop of weed seeds. The fifth is mulching too thinly to do any good — a centimetre of mulch is decoration, not mulching.
Another mistake is forgetting that mulch is not a substitute for feeding. Organic mulches feed the soil slowly, but hungry crops still need compost and, where needed, fertiliser. Plan feeding with our fertiliser calculator and keep the mulch doing its own job.
Frequently asked questions
What is the best all-round mulch? For most gardens, shredded leaves or garden compost are the best all-rounders: free or cheap, good for the soil and easy to apply. Wood chip is best for permanent plantings and paths; straw is best for vegetable beds.
How often should I replace mulch? Organic mulches break down, so top them up once or twice a year — usually in spring and autumn. If you can still see the soil through the mulch, it is time to add more.
Can mulch attract slugs? Yes, thick, damp organic mulch can shelter slugs and snails. It is still worth mulching — the benefits far outweigh the risk — but keep mulch away from stems, avoid over-thick layers near vulnerable seedlings, and use slug control methods as needed. See our guide to slugs and snails control.
Does mulch attract termites? Wood chip and bark near a house can shelter termites in some regions, though the risk is often overstated. Keep wood mulches a short distance from wooden structures, and check your local extension service for termite guidance in your area.
Can I mulch in winter? Yes — autumn mulching protects roots from frost and feeds the soil over winter. Just make sure the soil is moist before you mulch, and keep the mulch away from stems so it does not hold damp against the plant in cold weather.
The bottom line
Mulch is the highest-return job in the garden: it saves water, suppresses weeds, feeds soil life and protects roots. Choose the right material for the job, apply it 5–8 cm deep on moist, weeded soil, keep it away from stems, and top it up once or twice a year. For more on mulching, see our guides to straw mulch, wood chip mulch and leaf mulch, or browse the guides hub.