Mulching: What to Use, When, and How Thick
Owen Petrakis · Oct 6, 2026 · 5 min read
Quick answer
A layer of mulch suppresses weeds, holds moisture, and feeds the soil. Applied wrongly, it can smother plants.
Mulch is any layer of material spread over the soil surface. It is one of the most effective, lowest-effort jobs in the garden.
The best times to mulch are mid to late autumn and early spring, when the soil is moist but not frozen.
1 Why mulch
- ✓Blocks light so weed seeds do not germinate
- ✓Reduces evaporation, so you water less in summer
- ✓Insulates roots from extremes of heat and cold
- ✓Organic mulches break down and improve soil structure
2 Types of mulch
Organic mulches include garden compost, well-rotted manure, leaf mould, bark chips, and straw. Compost and manure feed the soil most. Bark is long-lasting and good for shrub borders. Inorganic mulches such as gravel and slate do not improve soil but suit dry, Mediterranean-style planting.
3 How to apply it
Weed the area first and water if the soil is dry. Spread mulch 5 to 8 cm deep. Keep it a few centimetres away from the stems of shrubs and trees — mulch piled against bark traps moisture and can cause rot.
4 Common mistakes
- ✓Mulching dry or frozen soil, which locks the problem in
- ✓Using fresh wood chip around small plants; it can temporarily take nitrogen from the surface
- ✓Spreading it too thinly to suppress weeds
- ✓Covering the crowns of perennials, which can rot them
5 Make your own
Collect autumn leaves in bin bags, add a splash of water, poke a few holes, and leave them for a year or two. The result, leaf mould, is a free and excellent mulch and soil conditioner.
This is general gardening information. Results depend on your climate, soil, and conditions. Follow label directions for any fertiliser or treatment, and check whether plants are toxic to pets or children before bringing them home.