Soil
Compost for Raised Garden Beds
Make compost about a third of a new raised bed's soil, then spread 1 to 2 inches on top every year. Use finished, crumbly compost that smells earthy, not sour.
| Type | Best use | Watch for |
|---|---|---|
| Homemade yard compost | Yearly top-dressing, mixing into new beds | Weed seeds if the pile never got hot |
| Municipal or bulk compost | Filling several beds at once | Woody chunks; ask what feedstock it's made from |
| Composted cow or horse manure | General vegetable beds | Herbicide residue from treated hay |
| Composted poultry manure | Heavy feeders, in small amounts | Very high nitrogen; can burn seedlings |
| Mushroom compost | Mixing into new beds | Can be salty; keep it under a quarter of the mix |
| Leaf mold | Improving soil texture | Low in nutrients on its own |
| Worm castings | A handful in planting holes | Too costly to fill a bed with |
How much compost to use
When you fill a bed from scratch, compost should make up about 30% of the mix, with the rest mostly topsoil and a little bark or perlite. Our soil recipe page has the full blend and bag counts.
More isn't always better. A bed that's half or more compost drains fast, sinks a lot as it decomposes, and can hold more phosphorus than plants use. Keep it between a quarter and a third of the volume. Half-rotted leaves and wood belong underneath instead; see base layers.
After the first year, feed the bed from the top. One inch spread over 32 square feet works out to about 2.7 cubic feet, or two 1.5-cubic-foot bags. Two inches takes about 5.3 cubic feet. For a 4x4 bed, halve those numbers.
Types of compost
Any finished compost will improve a bed, but they aren't identical. Plant-based compost from leaves and yard waste is mild and good for every crop. Composted manures carry more nutrients, so they suit hungry plants like tomatoes, squash and corn.
Poultry manure compost is the strongest. Mix it in a few weeks before planting and use about half as much as you would other compost.
Bulk compost from a city program or landscape yard is often the cheapest by far, and some towns give it away. Ask what goes into it. Compost made from grass clippings, hay or manure can carry broadleaf herbicides such as aminopyralid or clopyralid, which survive composting and curl the leaves of tomatoes, beans and peppers. If unsure, sow a few beans in a pot of it first; twisted, cupped leaves are the warning sign.
Good compost is dark brown, crumbly, and smells like a forest floor. If it's hot, slimy, or smells like ammonia, it isn't finished yet.
When to add it
Fall is the easiest time. Spread 1 to 2 inches after clearing out spent plants and let winter rain and worms work it in. Beds are ready to plant in spring with no digging.
Spring works too. Add compost two to three weeks before planting and mix it into the top few inches with a fork. Don't till deeply; it breaks up the soil structure you've built.
During the season, you can side-dress hungry crops with a half inch of compost around the base of each plant at midseason, then water it in.
Fresh, uncomposted manure is a different matter. Many extension services recommend working it in at least 90 to 120 days before you harvest any food crop, so fall is the only practical time to use it.
Making compost at home
A home pile can supply most of what a few raised beds need each year. Make it at least 3 feet wide, 3 feet deep and 3 feet tall so it holds heat.
Layer roughly two to three parts "browns" to one part "greens" by volume. Browns are dry leaves, straw, shredded cardboard and wood chips. Greens are kitchen scraps, coffee grounds, fresh grass clippings and garden trimmings. Keep the pile as damp as a wrung-out sponge.
Turn it every week or two with a fork. A well-built pile heats to 130 to 160°F in the center, which kills many weed seeds, and can finish in two to four months. An untended pile still works, just more slowly: plan on six months to a year. Leave out meat, dairy, oils, pet waste, diseased plants and weeds that have gone to seed.
Short on space? A closed bin or worm bin makes smaller amounts, or bury kitchen scraps 8 to 12 inches deep in an empty corner of a bed and plant over the spot after a few weeks.
Signs you need more
- The soil level has dropped well below the rim.
- The surface crusts over after rain or watering.
- Water puddles or runs off instead of soaking in.
- Plants are pale or slow even with steady water and sun.
- You see few earthworms when you dig.
Any one of these is a good reason to add an inch or two of compost this season. If the bed has sunk more than a few inches, refill it using the steps in our budget filling guide. For bagged products, Thrive Garden carries a range of soil amendments, and local garden centers stock compost too.
How to choose
You have a yard
Start a pile with fall leaves and kitchen scraps. It covers most of the yearly top-dressing for two or three beds.
You're filling new beds
Buy bulk compost by the yard and blend it into topsoil. Check the source for herbicide risk first.
Your crops are hungry
Use composted manure or add some poultry compost for tomatoes, squash and corn.
Your soil is heavy
Add leaf mold or plant-based compost to loosen it; it improves texture more than nutrients.
Related guides
Can a raised bed be filled with pure compost?
It's not a good idea. Pure compost settles a lot, dries out quickly, and can be too rich for some crops. Blend it with topsoil so it's about a third of the mix.
Is bagged compost as good as homemade?
Usually, yes, as long as it's finished and from a reliable source. Bagged compost costs more per cubic foot, so it makes the most sense for small beds and yearly top-ups.
Is it better to dig compost in or leave it on top?
Either works. Mixing it into the top few inches gets it to roots faster, while leaving it on top protects soil structure and lets worms do the work.