Mulching: keeping the soil moist for longer

Mulching means covering bare soil with a layer of material: straw, dead leaves, shredded branches… It is the simplest way to water less. It uses no water, so it remains possible whatever the restriction level.

What mulching does

• Less evaporation: sun and wind no longer reach the soil, which stays moist much longer after rain or watering.
• Cooler soil: roots suffer less during heatwaves.
• Fewer weeds: deprived of light, they hardly germinate, and they no longer take your plants' water.
• Living soil: a plant-based mulch slowly breaks down and feeds earthworms and soil life.
• Less crusting and run-off: rain soaks in instead of running off packed soil.

Which materials to choose

Plant-based materials, best because they enrich the soil:

• Grass clippings: free, but let them dry for a day or two and spread them thinly (2 to 3 cm), otherwise they ferment.
• Dead leaves: ideal in autumn, at the foot of shrubs and in flower beds.
• Straw or hay: the standard choice for vegetable gardens.
• Shredded branches (wood chips): long-lasting, perfect under trees, hedges and in beds.
• Flax or hemp mulch: light and clean, handy for beds and pots.
• Pine bark: decorative and long-lasting, rather for beds and acid-loving plants.
• Plain brown cardboard without coloured ink: under another mulch, to smother weeds on a new bed.

Mineral materials (gravel, slate, volcanic rock) last for years but do not feed the soil; they suit rock gardens and Mediterranean plants. Avoid plastic sheeting: it keeps rain out and breaks down into fragments.

How to mulch

1. Pick the right time: in spring, once the soil has warmed up (around May), or in autumn. Mulch laid on cold soil keeps it cold.
2. Weed, then lay the mulch on moist soil, right after rain (or watering, if your commune's decree allows it): mulch keeps moisture in, it does not create it.
3. Spread a thick layer: 5 to 10 cm for straw, leaves or wood chips; less for fine materials such as grass clippings.
4. Keep a few centimetres clear around stems: mulch against a stem or trunk holds too much moisture and can rot it.
5. Top up the layer during the season as it breaks down.

Mistakes to avoid

• Fresh wood chips dug into the soil: as they break down they use up the soil's nitrogen. Leave them on the surface, or use them under trees and shrubs rather than in the vegetable garden.
• Too thin a layer: under 5 cm, weeds come through and evaporation goes on.
• Slugs: straw shelters them. Keep an eye on young plants and keep the mulch a little away from seedlings.
• Mulching dry soil: the next rain will struggle to get through. Wait for rain, or water first if your commune's decree allows it.

What about the lawn?

You cannot mulch a lawn, but you can help it in the same way:

• mow higher in summer (7 to 8 cm): tall grass shades the soil;
• leave the clippings on the lawn ("mulching" mowing): they break down in a few days and limit evaporation;
• accept that it turns yellow during a drought: an established lawn usually greens up again with the autumn rains.

When watering is allowed, mulching combined with ollas or watering at the foot of plants lets you water much less often. When it is banned, mulching remains the best way to keep the water of the last rain.