How do I mulch a garden and why does it matter?
What mulch does for water, weeds and soil, which material to use where, and the mistakes that make it counterproductive.
- Difficulty
- beginner
- Time
- 2 hr
- Read
- 2 min
Short answer
Spread 5-8cm of organic matter over damp, weed-free soil, keeping it clear of plant stems and tree trunks. It suppresses weeds, holds moisture and feeds the soil as it breaks down — probably the highest-value hour in the gardening year.
Bare soil loses water, grows weeds, and loses structure under rain. Mulch addresses all three at once and improves fertility as it decomposes. The two things that make it fail are mulching dry soil and piling it against stems.
What you'll need
- Compost, bark or leaf mould
- Fork or spade
- Wheelbarrow (optional)
Step by step
- Weed thoroughly first.Mulch suppresses seedlings but not established perennial weeds, which grow straight through and are then harder to get at.
- Water the soil well, or mulch after rain.Mulch holds moisture in and also keeps rain out. Applied to dry soil it keeps it dry for months.
- Spread 5-8cm evenly.Thinner does not suppress weeds; much thicker can stop water and air reaching the roots.
- Keep it clear of stems and trunks.Leave a few centimetres of bare soil around each plant. Mulch piled against a stem holds moisture there and rots the bark.
- Choose the material for the job.Garden compost and well-rotted manure feed the soil. Bark chips last longer and look tidier but add little fertility. Leaf mould is excellent and free.
- Mulch in autumn or spring.Autumn protects the soil over winter; spring locks in moisture before summer. Either is far better than not at all.
- Top up annually.Organic mulch breaks down into the soil — that is the point. Expect to reapply each year.
- Use gravel or slate for drought-tolerant beds.It conserves water without adding fertility, which suits Mediterranean and alpine planting that dislikes rich soil.
Tips
- Fresh wood chip should not be dug into soil — it locks up nitrogen as it decomposes. On the surface as a mulch it is fine.
- Cardboard under a layer of compost smothers stubborn weedy ground effectively and breaks down within a season.
- Mulching keeps soil warmer in winter and cooler in summer, which noticeably reduces stress on shallow-rooted plants.
Common mistakes
- Mulching dry soil — It seals the dryness in. Water thoroughly first, or wait for rain.
- Piling mulch against stems and trunks — It holds moisture against the bark and causes rot, which can kill established shrubs and trees.
- Mulching over perennial weeds — Bindweed, couch grass and ground elder grow straight through and are then harder to reach and remove.
Questions people ask
How thick should mulch be?
Around 5-8cm. Thinner does not suppress weeds effectively; much thicker can prevent water and air reaching the roots.
What is the best mulch for a garden?
Garden compost or well-rotted manure if you want to feed the soil, bark chips if you want longevity and a tidy look, leaf mould if you want an excellent free option.