Mulching Guide: Benefits, Types and How to Apply

Why Mulch Matters

In nature, the soil is rarely bare. Leaves fall, plants die back, and a layer of organic material sits on the surface, slowly breaking down and feeding the soil. In a garden, we rake up leaves, pull out dead growth, and leave the soil exposed. Mulching simply restores the natural layer that the soil is missing.

The benefits of mulching are well documented. A 5cm layer of organic mulch reduces water loss from the soil by up to 70 percent, suppresses annual weeds by 90 percent, and can increase earthworm activity threefold within two years. Earthworms are the engine of healthy soil, mixing organic matter down into the root zone and creating drainage channels.

The Main Benefits of Mulching

Weed suppression

A 5cm layer of mulch blocks the light that annual weed seeds need to germinate. Seeds landing on the surface either fail to germinate or grow weakly and can be pulled out with two fingers. Perennial weeds such as bindweed and couch grass will come through mulch, so dig these out before mulching.

Moisture retention

Mulch acts as a blanket over the soil, reducing evaporation. In a dry summer, mulched soil stays moist for a week longer than bare soil. This means less watering, less drought stress, and healthier plants. The moisture retention benefit alone is worth the cost of the mulch in most UK gardens.

Soil temperature regulation

Mulch keeps the soil cooler in summer and warmer in winter. The roots of most plants prefer stable temperatures. A 5cm mulch can keep the soil 2 to 3 Celsius cooler in summer, which makes a real difference to shallow rooted plants such as rhododendrons and azaleas.

Soil improvement

Organic mulches break down over a year or two, adding organic matter to the top layer of the soil. This improves soil structure, feeds earthworms and other soil life, and slowly releases nutrients to the plants. The effect is cumulative: mulch for a few years and the soil becomes darker, richer and easier to work.

Erosion control

On slopes or in areas of heavy rain, mulch prevents soil erosion. Rain hits the mulch rather than the bare soil, and the mulch slows the water as it runs off. This is particularly useful on newly planted banks and in exposed gardens.

Types of Mulch

Bark mulch

Bark is the most popular mulch in the UK. It is clean, attractive, slow to break down, and relatively cheap. Landscaping bark, sold in 50 or 100 litre bags, costs 6 to 10 pounds per bag and covers about 2 square metres at 5cm depth. Composted bark is darker and breaks down faster, feeding the soil more quickly.

Bark is best for ornamental beds and around trees and shrubs. Avoid using it on vegetable beds because it ties up nitrogen as it breaks down, and do not use it around low growing plants such as strawberries where it can harbour slugs.

Garden compost

Home made compost is the best all round mulch if you have enough of it. It is free, full of soil life, and breaks down to feed the soil directly. The downside is that most gardens do not produce enough compost to mulch everything. Use it on the beds that need it most: vegetable beds, hungry feeders such as roses, and newly planted specimens.

A rough guide is that a 1 cubic metre compost bin produces enough compost to mulch about 5 square metres at 5cm depth. Most gardens need 4 to 6 bins to be self sufficient in compost.

Farmyard manure

Well rotted farmyard manure, usually horse or cow, is a rich mulch for hungry feeders. It must be at least two years old, dark and crumbly, with no smell. Fresh manure will burn plant roots and encourage soft growth that is damaged by frost.

Manure is ideal for roses, fruit trees, vegetable beds, and heavy feeders such as dahlias and delphiniums. Apply in late winter or early spring. A 50 litre bag costs 5 to 8 pounds and covers about 1.5 square metres.

Leaf mould

Leaf mould is made by composting autumn leaves on their own for two years. The result is a dark, crumbly material that is excellent as a mulch and soil improver. It is not rich in nutrients but it improves soil structure dramatically and is free if you have deciduous trees.

Make leaf mould by putting leaves in a wire mesh cage or black plastic bags with holes punched in. Leave for two years. Oak and beech leaves make the best leaf mould. Pine needles make an acidic leaf mould that is perfect for mulching acid loving plants.

Gravel and stone

Gravel and stone mulches are non organic, so they do not feed the soil, but they suppress weeds and retain moisture. They are useful for Mediterranean style plantings, alpine beds, and around plants that hate winter wet such as lavender and rosemary.

Lay a weed suppressing membrane under the gravel to prevent weeds coming through. A 5cm layer of 10mm gravel over membrane costs about 8 to 12 pounds per square metre including the membrane.

Mushroom compost

Spent mushroom compost is a cheap, slightly alkaline mulch that is excellent for clay soils. It contains chalk and breaks down heavy clay over a few seasons. Avoid using it on acid loving plants such as rhododendrons and camellias. A 50 litre bag costs 4 to 6 pounds.

Cocoa shells

Cocoa shells are a byproduct of chocolate manufacturing. They make an attractive dark mulch that smells of chocolate and breaks down slowly. They are expensive but look good in ornamental beds. Avoid if you have dogs, as cocoa can be toxic to them.

Mulch Comparison Table

When to Mulch

The best time to mulch is late winter or early spring, after the worst of the winter but before the spring growth spurt. Late February to mid March is ideal in southern England. The soil is warming up, weeds have not yet germinated, and the mulch will lock in the winter moisture that the soil is holding.

A second mulching window is in autumn, after leaf fall. Autumn mulching protects the soil from winter rain, insulates plant roots from frost, and gives the worms time to work the mulch into the soil over winter.

Avoid mulching in summer when the soil is dry. Mulch on dry soil acts as a barrier that prevents rain reaching the roots. Water the soil thoroughly before mulching in summer, or wait until autumn.

How to Apply Mulch

Step 1: Weed thoroughly

Mulch suppresses annual weeds but does not kill perennial weeds. Dig out bindweed, couch grass, dandelions and ground elder before mulching. If you mulch over perennial weeds, they will come through and you will have wasted your money.

Step 2: Water if dry

If the soil is dry, water it thoroughly before mulching. The mulch will lock in the moisture. If you mulch dry soil, it will stay dry under the mulch until you water it enough to wet the mulch and the soil beneath.

Step 3: Apply the mulch

Apply a 5cm layer of mulch across the bed. For trees and shrubs, mulch a circle at least 60cm wide around the base. Do not heap the mulch against the trunk or stem, as this can cause rotting. Keep a 5cm gap clear around the base of each plant.

Step 4: Top up annually

Organic mulches break down over a year or two. Top up annually with a 2cm layer to maintain the 5cm depth. After 3 or 4 years, you may need to dig the residual mulch into the soil before applying a fresh thick layer.

Mulching Specific Situations

Roses and shrubs

Mulch roses and shrubs with well rotted manure or compost in early spring, after pruning. Apply a 5cm layer in a 60cm circle around each plant. This feeds the plant, retains moisture, and reduces blackspot by preventing rain from splashing soil onto the leaves. See our rose profile for more on rose care.

Vegetable beds

Mulch vegetable beds with compost or manure in late winter, before sowing. This can be left on the surface or dug in lightly. For growing crops, mulch between rows with grass clippings or compost to suppress weeds and retain moisture. Avoid bark on vegetable beds.

Trees and hedges

Mulch newly planted trees and hedges with bark or compost in a 60cm circle for the first 3 years. This keeps grass away from the young roots and dramatically improves establishment. See our guide to hedge cutting for related care.

Borders

Mulch ornamental borders in late winter with bark or compost. The mulch suppresses spring weeds and locks in winter moisture. Pull the mulch back from emerging bulbs and perennials so they are not smothered.

How Much Mulch Do You Need

Mulch is sold by volume, usually in litres or cubic metres. To cover a bed to 5cm depth, you need 50 litres per square metre, or 0.05 cubic metres. A 10 square metre bed needs 500 litres, or half a cubic metre.

Bulk bags of mulch are 1 cubic metre and cost 80 to 150 pounds depending on the type. They cover 20 square metres at 5cm depth. Smaller bags of 50 to 100 litres are available at garden centres but work out 2 to 3 times more expensive per litre.

Common Mulching Mistakes

Mulching too thin

A 2cm layer of mulch looks nice but does almost nothing. Weeds come through, moisture still evaporates, and the soil does not improve. Apply 5cm minimum, 7cm if you can afford it.

Mulching over weeds

Perennial weeds will come through any depth of mulch. Dig them out first. If you have a serious infestation, lay cardboard under the mulch to smother them. Cardboard breaks down in a year and is an effective weed barrier.

Using the wrong mulch

Mushroom compost on rhododendrons will slowly kill them. Bark on vegetable beds ties up nitrogen. Cocoa shells where dogs can reach them can poison them. Match the mulch to the situation.

Not watering first

Mulch on dry soil keeps the soil dry. Always water thoroughly before mulching, or wait until after rain. See the RHS guidance on mulches for more on choosing and applying mulches.

Mulching on a Budget

If you cannot afford to mulch the whole garden, prioritise. Newly planted trees and shrubs benefit most, because they are establishing their roots. Roses and other heavy feeders come second. Established shrubs and perennials in good soil can wait.

The cheapest mulch is what you can make yourself. A compost bin or two, a leaf mould pile, and a small area of comfrey or nettles for liquid feed will give you a steady supply of free mulch material. See our low maintenance plants guide for ideas on plants that need less mulching.

Frequently Asked Questions

Can I use grass clippings as mulch?

Yes, but with care. A thin layer, 1 to 2cm, is fine around established plants. A thick layer of grass clippings forms a slimy mat that excludes air and smells. Add grass clippings in thin layers, mixing with dry material if possible. Never use clippings from a lawn treated with weedkiller.

How often should I mulch?

Top up organic mulches annually to maintain a 5cm depth. After 3 to 4 years, the residual mulch may have built up enough to need digging in. Gravel and stone mulches do not need topping up.

Will mulch attract slugs?

Some mulches, particularly grass clippings and bark, can harbour slugs. On the plus side, they also harbour ground beetles and other predators that eat slugs. If slugs are a serious problem, use a coarser mulch such as gravel around vulnerable plants. See our hosta profile for slug control on susceptible plants.

Is it OK to mulch in summer?

Only if you water the soil thoroughly first. Mulch on dry soil prevents rain reaching the roots. If the soil is already moist, summer mulch will help retain that moisture. If the soil is dry, water it deeply before mulching.

Final Thoughts

Mulching is the single most useful thing you can do for your garden soil. It suppresses weeds, retains moisture, regulates temperature, and feeds the soil life that feeds your plants. The cost is modest, the work is light, and the benefits accumulate over years. If you do one thing in your garden each spring, mulch.

If you would like help sourcing mulch in bulk, or with applying mulch across a larger garden, get in touch with our team. We can supply and apply mulch across the Chilterns area.

Further Reading

• Low maintenance plants for the Chilterns
• Why is my lawn full of moss?
• Garden maintenance service
• Roses plant profile

Sources and citations

This article draws on the following sources. Specific claims are cited inline where relevant.

1. CGM field records (2024-01. Site observations from gardens across Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire.
2. Royal Horticultural Society (2024). RHS Gardening Advice and Plant Finder. Available at rhs.org.uk.
3. Met Office (2024). Regional climate averages, South East England. Available at metoffice.gov.uk.
4. British Geological Survey (2024). Soil parent material data for the Chilterns and Thames Valley. Available at bgs.ac.uk.