Building Healthy Soil | UC Master Gardener Program of Contra Costa County

Sustainable Gardening - Building Healthy Soil

The following information describes how to build healthy soil in a home garden.

Healthy Soil is a living system that includes:

Inorganic material—rock/mineral particles.
Air (especially oxygen) and water.
Organic material—living organisms: roots, worms, microbes, etc.; decomposing/decomposed organisms.

A self-balancing natural ecosystem with stable populations of plants & soil organisms.
Approx. 5% organic matter with a stable, slightly acidic pH that keeps nutrients supplied in plant-available forms.
Continuous nutrient cycling throughout the soil system. Plant roots exude sugars & proteins that attract & feed
soil organisms. As these organisms die/decompose or are eaten by others, nutrients are released back to plants.
Strong “crumb” or granular soil structure, with a mixture of pore sizes that hold both air and water.

Life in the soil creates soil structure

Soil organisms decompose organic matter, slowly producing humus, which is highly resistant to further breakdown.
Soil organisms produce glues and filaments that bind tiny mineral particles and humus together into soil crumbs.
Worms and other burrowing creatures continuously open pathways for roots, air, and water.

Maintains critical soil air space while acting as a rainfall reservoir... soil becomes like a sponge.
Drains excess water quickly, avoiding detrimental, disease-friendly anaerobic conditions.
Helps soil resist erosion & compaction.
Allows beneficial soil organisms to flourish; they maintain the structure & keep the nutrient cycle going.

Disruption of the soil system leads to soil compaction, erosion, infertility, etc.

Excessive disturbance, especially rototilling and construction
Working or even walking on wet soil
Excessive watering; excessive dryness
Leaving soil bare (but leave some bare for native bees)
Chemical fertilizers, pesticides, chlorinated water (includes chloramines)
Excessive pruning/shearing of plants (stimulates excess growth, depletes soil nutrients)

Returns nutrients to the soil; keeps waste out of the landfill.
Replenishes/supports populations of beneficial soil organisms.
Helps form soil aggregates, improving soil structure.
- Clay soils: improve aeration, water infiltration & percolation.
- Sandy soils: increase water-holding capacity, which helps hold nutrients.
Organic mulches decompose in place, providing slower but similar benefits. Sheet mulching is especially effective.
If you’re short on time, keeping the soil covered with an organic mulch is the simplest approach.

Work with, not against, the ecosystem...handle with care; put back what you remove.
Avoid compaction & excessive soil disturbance.
Reduce pruning & waste—right plant, right place; design beds carefully.
Avoid chemical/synthetic fertilizers, overfertilizing, overwatering, and severe underwatering.
Use compost and mulch to
- supply/recycle soil microbes & nutrients,
- nurture the soil organisms that partner with your plants,
- and thus, to keep the engine running!

Below are a few ways to build healthy soil

Apply disease and weed-free organic mulch 2-4” thick, keeping it away from the root crowns of plants.
Apply coarser mulch more thickly and finer-textured mulch more thinly.
Reapply as needed.

Cut or mow weeds.
Apply a thin layer of compost and cover with dampened newspaper or cardboard, overlapping edges.
Cover with 2-4” of mulch as above.
Keep damp to hasten decomposition and soil enrichment.

UC Master Gardener Program of Contra Costa County
2380 Bisso Lane, Concord, CA 94520