What is living in my soil?
A handful of healthy soil holds a huge number of organisms, most too small to see. Bacteria and fungi break down organic matter. Protozoa and nematodes feed on them and release nutrients. Earthworms and insects mix and aerate the soil.
Together they build crumb structure, cycle nutrients and sometimes help plants resist disease. You do not manage each organism. You manage the conditions they live in.
The mix of organisms changes with the food you give them. Fresh plant residues favor bacteria, and woody materials favor fungi, so a range of materials supports a range of life.
How does compost help?
Compost adds organic matter that feeds soil life and improves structure and water holding. Finished compost also supplies some nutrients, though the amount varies with the materials used.
It is not a substitute for a soil test. Compost can add nutrients that are already high in your soil, so test first and apply with the results in mind.
Compost is not magic, and it does not fix compaction, drainage or pH on its own. Look at these other conditions too, and use a soil test to see where you stand.
- Feeds soil organisms
- Improves crumb structure
- Helps hold water and nutrients
- Adds some nutrients that vary by material
What makes compost good?
Good compost comes from a balance of carbon-rich materials, such as leaves and straw, and nitrogen-rich materials, such as kitchen scraps and manure. It also needs moisture and air. Piles that are too wet turn smelly, and piles that are too dry stall.
Finished compost looks dark and crumbly and smells earthy. If it still smells sour or contains recognizable scraps, it needs more time. Ask your extension office for methods that suit your scale.
Turning a pile adds air, and some gardeners use a thermometer to track how the pile behaves. Because heat and time targets matter for food safety, follow current extension guidance instead of rules of thumb you read online.
- Carbon-rich: leaves, straw, shredded paper where allowed
- Nitrogen-rich: kitchen scraps, manure, fresh plant trimmings
- Moisture like a wrung-out sponge
- Air through turning or a well-built pile
Is it safe to use?
Compost that contains manure needs care when used on food crops. Manure can carry disease organisms, and proper composting is meant to reduce them. Food safety guidance for gardens and farms covers handling, timing and wash practices.
Ask your extension office for current guidance on manure compost and food crops. Also be careful with inputs from outside sources, since hay, manure and grass clippings can carry herbicide residues that damage plants. Ask suppliers about their sources.
Wash hands after handling compost, wear gloves and keep children and pets away from active piles. Wash produce grown in or near compost before eating. If you are unsure about a source, hold the material in a separate pile and use it on ornamental beds first. Observe how plants respond for a season before putting it on food crops.
How do I use compost wisely?
Spread compost on the soil surface or work it lightly into planting areas. A soil test and the needs of your crop guide how much to use. More is not always better, and excess can cause nutrient problems or runoff.
Keep compost away from wells, streams and ditches, and store piles where rain will not wash them away. Local rules on composting at your scale vary, so check with your county.
Your extension office can tell you whether to apply compost before or after planting for your crops, and how long to wait between application and harvest where manure is involved.
What are other ways to feed soil life?
Compost works best as part of a larger plan. Cover crops, mulch, crop residues and reduced tillage all feed soil organisms and protect their habitat. Rotating crops also changes what the soil community receives.
Avoid claims that a single product or compost tea will fix a soil. Tested results and your own observation of plant growth and soil condition are better guides.
Notice how your plants and soil respond over several seasons. That record is more useful than any single test.
- Cover crops and living roots
- Mulch and crop residues
- Less tillage
- Crop rotation
Key takeaways
- Soil life drives nutrient cycling and structure, and compost feeds it.
- Test your soil before adding compost.
- Use caution with manure compost on food crops and with outside inputs that may carry herbicide residue.
- Pair compost with cover, mulch and less disturbance.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.