Bare, open soil is the exception in the garden, not the rule. In nature the earth is always covered, with leaves, dead plants or living green. Mulching imitates exactly that and brings the garden several advantages at once.
But mulch is not just mulch. The wrong material in the wrong place can do more harm than good, from a rotting heap of grass to hungry vegetables under bark. Whoever knows what belongs where turns a simple layer into a powerful tool.
What mulching does
A mulch layer works on several levels at once. It holds moisture in the soil because it slows evaporation, so you need to water less often. It shades the earth, so weeds hardly germinate. And it protects the soil from capping by rain and from drying out in the sun.
On top comes the long-term gain: organic mulch is broken down bit by bit by worms and microbes and so builds humus, much as with compost. The soil turns looser, darker and more alive. Mulching is therefore soil care and water-saving in a single move.
Which material where
The commonest mistakes arise because the wrong material is used. A short overview helps.
The right mulch in the right place
- Grass clippings: only thin
Nitrogen-rich and quickly available, ideal for vegetables. But always apply only thinly and slightly dried. Fresh and heaped thick, it clumps and rots into a slimy, smelly layer.
- Straw: the vegetable classic
Loose, airy and slow to rot. Perfect for tomatoes, strawberries and squash, because the fruit lies clean on the straw instead of in the mud.
- Leaves: free in autumn
They fall for free and cover beds and perennials over winter. Mix in some coarse shreddings to keep them airy, so they do not mat down.
- Bark and shreddings: ornamental only
For shrubs, paths and ornamental woody plants. On the vegetable bed, though, taboo, because as they rot they bind nitrogen and take it from the hungry crops.
How to mulch properly
Weed and water first
Before mulching, remove the weeds and water through in dry spells. The mulch layer preserves the state of the soil, so mulch a clean, moist soil.
Mulch onto warm soil
Mulch only once the soil has warmed in early summer, roughly from May. A thick layer on cold, wet earth keeps the soil cool for a long time and slows growth.
Layer thin and to suit
Apply the mulch about two to five centimetres thick, fine material thinner, coarse a little higher. Keep a small gap from stems and the base of the trunk, so nothing rots there.
Top up and observe
Organic mulch rots and grows thinner. Top it up over the season. Watch whether slugs gather under the damp layer; then air it or keep it away from young plants.
The soil wants to be covered. But grass clippings only thin, bark only in the ornamental garden, and mulch never against the stem.
The core rule of mulching
Frequently asked questions
Why does my grass-clipping mulch rot?
Because it lies too fresh and too thick. Fresh grass contains a lot of water and nitrogen; heaped thick, it clumps and rots into a slimy layer. Always apply it only thinly and let it dry off a little first.
May I put bark mulch on the vegetable bed?
Better not. Bark and wood shreddings bind nitrogen as they rot and take it from the vegetable plants. Use bark mulch for shrubs, ornamental woody plants and paths. For vegetables, straw, grass clippings and leaves are suitable.
Does mulching encourage slugs?
It can encourage them, because they love the damp, sheltered layer. In a healthy garden with beneficials it is usually no big problem. But around young, sensitive plants you mulch sparingly to be safe.
When is the best time to mulch?
Once the soil has warmed in early summer, usually from May. Too early on cold earth, the mulch keeps the soil needlessly cool. Over winter, by contrast, a layer of leaves protects the beds from cold and erosion.
Do I still have to feed under the mulch?
Organic mulch itself provides nutrients as it rots and replaces part of the feeding. With woody mulch or hungry heavy feeders, you add some organic fertiliser as well, to balance the nitrogen binding.
