Composting & Soil: A Complete Guide

Almost every gardening problem traces back to the soil eventually. Plants that sulk, lawns that thin out, beds that bake hard or stay soggy, vegetables that never quite produce: most of the time the fix is not a new plant or a stronger fertilizer but better ground for roots to grow in. This guide is for homeowners who want to build that ground, whether you are breaking in a new-build yard of compacted clay, starting a first compost bin, or just trying to work out which bag of soil to buy at the garden center. It runs in the order the work usually happens: learning your soil type, testing it, fixing drainage and compaction, making compost, choosing bought-in soil and amendments, feeding plants, filling containers, and finishing with mulch. Each section links to our detailed guides, so you can dig into the step you are on and come back for the next one.

In this guide

1. Know your garden soil: clay, sand and loam
2. Test your soil before you amend it
3. Fix compacted, poorly draining and eroding soil
4. Start composting at home
5. Compost problems, worm bins, bokashi and leaf mold
6. Buying topsoil, compost and manure
7. Compost vs fertilizer: feeding your soil and plants
8. Potting soil, potting mix and seed starting
9. Mulch: types, depth and how much you need
10. Composting and soil gear worth buying
11. Frequently asked questions

Know your garden soil: clay, sand and loam

Soil texture is the mix of sand, silt and clay particles, and you cannot change it much, but you can change how it behaves. Take a handful of moist soil and squeeze. If it forms a sticky ribbon that holds together, you have clay; if it feels gritty and falls apart, it is sandy; if it holds a loose ball that crumbles when poked, you are lucky enough to have loam. A jar test (soil shaken with water and left to settle into layers overnight) gives a rough percentage. Our guides to clay vs sandy vs loam soil and telling clay from sandy soil walk through both tests.

The fix for both extremes is the same: organic matter, added every year. In clay it opens up pore space so water drains and roots can breathe; in sand it acts like a sponge that holds water and nutrients. Read how to improve clay soil for gardening, amending clay soil at planting time and how to amend sandy soil. Skip the old advice to add sand to clay, which can make something closer to concrete, and be skeptical of gypsum, which only helps in specific sodic soils; lime vs gypsum for soil explains when each is worth it.

Test your soil before you amend it

Guessing at soil chemistry is how gardens end up with too much phosphorus and the wrong pH. A soil test every three to four years tells you pH, the major nutrients and organic matter, and it is cheap through your state’s Cooperative Extension office. Take a dozen small samples from four to six inches deep across the bed, mix them in a clean bucket, and send about a cup. Our guide on how to test soil pH and adjust it covers sampling, and how to read a soil test report translates the results into what to add.

Most vegetables, flowers and lawns are happiest around pH 6.0 to 7.0. Lime raises pH and sulfur lowers it, but both work slowly, over months, so make corrections in fall for the following season. For quick checks between lab tests, home meters and strips can point you in the right direction; see soil pH meter vs test strips for which is more accurate.

Fix compacted, poorly draining and eroding soil

Compaction is the hidden problem in most yards, especially around new houses where heavy equipment squashed the subsoil. Signs include puddles that linger, water that runs off instead of soaking in, and roots that grow sideways. Loosen beds with a garden fork, add two to three inches of compost, and then stop walking on them: permanent paths and raised beds prevent compaction from coming back. Our guide on how to fix compacted soil covers lawns and beds, and why your soil is not draining helps separate compaction from a high water table or a hardpan layer.

The opposite problem is soil that sheds water like a duck’s back. Dry potting mix and peat-heavy beds can turn water-repellent; why soil turns hydrophobic explains how to rewet it. On slopes, bare soil washes away in every storm, so cover it with plants, mulch or erosion blankets as described in how to stop soil erosion on a slope. Around the house, soil should fall away from the foundation by roughly six inches over the first ten feet; see how to grade soil around a foundation. When you are ready to plant, our step-by-step on how to prepare soil for planting pulls it all together.

Start composting at home

Composting turns kitchen scraps, leaves and garden trimmings into the best soil amendment there is, for free. If you are new to it, start with composting for beginners and our step-by-step guide to how to make compost. The core recipe is simple: mix “greens” (nitrogen-rich scraps, grass clippings, coffee grounds) with “browns” (dry leaves, straw, shredded cardboard) at roughly two to three parts brown to one part green by volume, keep the pile as damp as a wrung-out sponge, and give it air. Green vs brown compost materials lists what goes in each column and what to leave out (meat, dairy, oily food, diseased plants and pet waste).

Next, pick a method. A hot pile of at least three feet on each side, turned every week or two, can finish in two to three months and kills most weed seeds; a cold pile you simply add to finishes in a year or so with almost no effort. Hot vs cold composting compares the two, and how to make compost faster covers shredding, turning and moisture tricks. No room for a bin at all? Trench composting means burying scraps directly in the bed.

Your compost bin can be as simple as a ring of wire fencing. Our plans for how to build a compost bin and pallet, wire and bin designs cost very little, and keen gardeners graduate to a three-bin compost system so one batch can finish while another fills. If you would rather buy, read compost tumbler vs compost bin first: tumblers are tidy and easy to turn but hold less and can go slimy without enough browns.

Compost problems, worm bins, bokashi and leaf mold

Most compost problems come down to the balance of greens, browns, water and air. A pile that smells like ammonia or rotten eggs has too many greens or too little air; add browns and turn it, as explained in why compost smells. A pile that just sits there is usually too dry, too small or too heavy on woody browns; see why compost is not breaking down.

Apartment dwellers and anyone with lots of kitchen scraps should look at worms. A worm bin under the sink or in the garage processes food waste into castings, one of the richest amendments you can make. Start with our vermicomposting guide or worm composting for beginners, and compare worm castings vs compost. Bokashi is a fermentation method that handles meat and dairy too; read the bokashi composting beginner’s guide and how to make bokashi compost.

Fall leaves deserve their own pile. Shredded leaves kept damp in a wire cage break down into crumbly leaf mold in about a year, a superb mulch and soil conditioner. See how to make leaf mold and compost vs leaf mold. More on compost: how to make compost tea, whether compost tea beats fertilizer.

Buying topsoil, compost and manure

Few gardens make enough compost for everything, so most of us buy some. Know what you are getting. Topsoil is bulk fill for leveling and building up grade; compost is the amendment you mix into it or spread on top. Our comparisons of compost vs topsoil, when to use topsoil or compost and topsoil vs garden soil clear up the labels. For anything over a few cubic yards, bulk delivery is usually cheaper and better quality than bags, as explained in bagged vs bulk soil; ask the supplier what is in the mix and look at it before it is dumped.

Manure is a great soil builder but should be well aged or composted before it goes near vegetables, since fresh manure can burn plants and carry pathogens. Read manure vs compost and chicken manure vs cow manure (chicken is far stronger). Mushroom compost is cheap and rich but can be salty and alkaline, so keep it away from blueberries and azaleas: see mushroom compost vs manure and mushroom compost vs regular compost.

Compost vs fertilizer: feeding your soil and plants

Compost and fertilizer do different jobs. Compost feeds soil life and improves structure but is low in nutrients; fertilizer delivers a measured dose of nitrogen, phosphorus and potassium. A well-composted bed often needs very little else, and a soil test tells you what is truly missing. Our guide to compost vs fertilizer explains how they work together, and organic vs synthetic fertilizer weighs speed, cost and soil health.

Form matters as much as source. Slow-release granules feed for weeks to months and suit lawns and shrubs; liquids act fast and suit containers and heavy feeders. Compare slow-release vs quick-release fertilizer, slow-release vs liquid and liquid vs granular fertilizer. Popular home remedies are often overrated: coffee grounds are a modest compost ingredient rather than a fertilizer, and Epsom salt only helps where a test shows magnesium is low. For turf feeding schedules, see our lawn care guide.

Potting soil, potting mix and seed starting

Never fill containers with garden soil. In a pot it compacts, drains poorly and suffocates roots. Use a soilless potting mix built from peat or coir, bark, and perlite, which stays light and airy. Our explainers on potting mix vs garden soil and potting soil vs potting mix decode the confusing bag labels. Refresh the top few inches of container mix each spring, and replace it entirely every couple of years as the bark breaks down.

For seed starting, a fine, sterile seed-starting mix prevents damping off. Soil blocks (compressed cubes of mix with no pot at all) give seedlings stronger roots and avoid transplant shock; see our soil blocking guide. For choosing pots, drainage and mixes for specific plants, the houseplants and containers guide and vegetable gardening guide go further.

Mulch: types, depth and how much you need

Mulch is the finishing layer that protects all the work underneath. It holds moisture, smothers weed seeds, evens out soil temperature and, if it is organic, feeds the soil as it breaks down. Our mulching guide covers the basics: two to three inches deep on beds, pulled a few inches back from stems and trunks (no “mulch volcanoes” around trees), topped up once a year. Work out quantities with how much mulch you need; one cubic yard covers about 100 square feet at three inches.

Choosing a type is mostly about where it is going. Browse types of mulch, then compare wood chips vs bark mulch, hardwood vs softwood and cedar vs pine for ornamental beds, and straw vs hay for vegetables (straw, since hay is full of seeds). Organic mulches beat rubber mulch for plant health, and dyed vs natural mulch explains what is in colored products. More comparisons: hardwood vs rubber, mulch vs rock, compost vs mulch, cover crops vs mulch for vegetable beds. A white or yellow crust on fresh mulch is usually a harmless slime mold; see why mulch molds.

Mulching a large property is heavy, repetitive work, and many homeowners hand it off along with planting. Our mulching and planting services page connects you with local crews, and the landscaping and hardscaping guide covers bed design and edging.

Composting and soil gear worth buying

Compost: best compost bins, best compost tumblers, best worm composters, best compost aerators and turners, best compost starters.
Soil and mixes: best bagged compost, best potting mix, best soil blockers, best soil scoops.
Testing and feeding: best soil test kits, best soil moisture meters, best soil thermometers, best fertilizer spreaders.

Frequently asked questions