Mulch is a covering of straw, leaves, chips or similar material over the soil that shades it, cools it and slows the loss of water from the surface, and it also suppresses weeds that would draw water. Water the soil deeply first, then lay mulch 4-6 inches deep, kept about 2 inches from stems and trunks. How much water a mulch saves depends on the climate, the material, the depth and the soil, so measure it on your own beds instead of relying on a quoted percentage.
Mulching is covering the soil surface with a layer of organic or inorganic material to reduce evaporation, suppress weeds and moderate soil temperature.
Mulch Works By Shading, Insulating And Suppressing Weeds
Water leaves bare soil by evaporation from the surface. A layer of mulch shades the soil from the sun, slows the wind at the surface, insulates against temperature swings and, if thick enough, smothers weeds that would otherwise draw on the same water. It also feeds soil life as it rots.
The carrier guide (Drought Resilience & Water-Efficient Agriculture) says a 4-6 inch layer of organic mulch reduces evaporation by 50-70%. The related guide Mulching puts the cut in water loss at 70-80%. Neither gives a source, and they disagree; the real figure depends on the material, the depth, the weather and what is being compared. Treat both as an indication that mulch matters, not as a number to calculate with.
What You Need
- Mulch material in quantity (Mulch Types and Application Depth).
- Water, for the first soaking.
- Hands and a fork.
Method
Step 1: Water first. The carrier says never to mulch dry soil: water deeply and then apply mulch to lock in the moisture.
Step 2: Spread the mulch evenly to the depth for the material, 4-6 inches for straw or leaves.
Step 3: Keep it 2 inches off stems and trunks to prevent rot and rodent shelter, as the carrier advises.
Step 4: Refresh it each year, since it rots.
Step 5: Measure the effect. Take soil samples at 10 cm from a mulched and an unmulched patch after a dry spell and compare water content by weighing wet and dried soil: water content (dry basis) = (wet − dry) ÷ dry × 100.
Common Mistakes
- Mulching dry soil — it keeps the dry soil dry.
- Piling mulch against stems — rot and rodents.
- Mulching too early in spring — it keeps cold soil cold and slows warming.
Safety
Dry mulch burns
Dry straw, hay and wood chips ignite from sparks and cigarettes, and large heaps of fresh chips can heat and catch fire on their own. Keep mulch away from buildings, flues and fires, and spread it rather than leaving deep stockpiles.
What’s Next
- Learn next: Mulch Types and Application Depth — choosing the material
- Combine with: Soil Organic Matter and Water Holding Capacity — the longer-term fix