Soil Cover: Never Leave Ground Bare

What it is

A permanent layer over the soil surface. Wood chips, straw, leaves, living plants, or a crust of moss.

Look at any forest floor. Nothing is bare. That is the rule.

Why bare soil dies

Direct sun pushes surface temperatures above 50°C on a hot afternoon. Bacteria, fungi, and protozoa cook in the top centimeters. Survivors retreat deeper, abandoning the zone where roots and microbes trade.

Rain hits like hammers. Each drop shatters the aggregates that hold pore space open. The surface seals into a crust. Water sheets sideways instead of soaking in.

That is erosion. Centuries of soil formation, gone in one storm.

Wind finishes the job. The soil food web cannot work without a stable roof. Masanobu Fukuoka spent decades watching this on his family farm. His conclusion: nature never leaves ground uncovered. Bare soil is a human invention.

Three kinds of cover

Organic mulch. Wood chips, straw, hay, shredded leaves, bark, grass clippings, compost. Shades the surface, buffers temperature, holds moisture, and decomposes into humus. The breakdown is the point. Each cycle adds another layer.

Living cover. Roots in the soil year-round. Cover crops like clover, rye, and vetch feed mycorrhizal fungi through root exudates. Standard in orchards and food forests, where creeping thyme or white clover holds the ground.

Inorganic cover. Gravel, stone, landscape fabric, plastic. Blocks light and evaporation but feeds nothing. Narrow uses only: gravel around Mediterranean herbs that need sharp drainage, or black plastic to solarise a weedy patch before planting. Never your default.

Pick the material

Wood chips belong on paths, around trees, and in perennial beds. Slow to break down. Strong weed suppression. Builds the fungal-dominated biology that woody plants want. Geoff Lawton has regenerated degraded ground in three to five years with thick chip mulch alone.

Keep fresh chips a few centimeters off vegetable stems. The carbon ties up surface nitrogen at the contact line, but the effect is shallow.

Straw is the vegetable garden default. Light, easy to spread, lets seedlings push through, gone in one season. Pairs well with no-dig over compost. Buy straw, not hay. Hay carries grass seed.

Leaf mould is the best mulch for trees and shade beds. Two-year-old leaf mould holds water like a sponge and matches the forest floor. Free if you have deciduous trees.

Depth and timing

8 to 15 cm is the working range for most materials. Thinner, weeds win. Thicker, rain bounces off and the layer below goes anaerobic.

Wood chips can go to 20 cm because the structure stays open. Grass clippings cap at 5 to 8 cm or they mat into slime. Straw sits at 10 to 15 cm.

For moisture, mulch after a deep watering once spring soil has warmed. For winter, mulch in late autumn after the soil cools but before hard frost. For new plantings, mulch the day you plant. Every bare day is an invitation.

Always pull mulch 5 cm back from stems and trunks. Bark rot starts where wet mulch meets living wood.

When it goes wrong

Matted grass clippings going black and sour. Pull them off, fluff with straw, restart.

Voles tunneling under deep straw in winter. Pack the first 30 cm around fruit tree trunks with gravel instead.

Hydrophobic wood chips repelling rain after a long dry spell. Scratch the surface with a rake before the next storm.