Your raised bed soil isn't used up at the end of the season. Here's why it settles, how to refresh it with compost, and why replacing it is almost never the answer.
What you need
At the end of the first season a raised bed looks lower than you left it, and the instinct is that the soil is spent and needs replacing. It isn’t, and it doesn’t. Here is what happened and what to do about it.
The soil settled. A new bed’s soil is full of air pockets and coarse organic matter, and over a season that organic matter decomposes and the whole thing compacts. A new bed can lose as much as half its height in the first year. That is normal, and the soil is still far from used up.
Each season, top the bed up with compost. Spread a quarter-inch to an inch of finished compost over the surface, and either work it into the top several inches or, for a no-till bed, leave it for the worms to pull down. That one habit restores the volume the settling took, and it replenishes the organic matter and nutrients that decomposition and last year’s harvest drew down. If the level dropped a lot, add more of a soil-and-compost blend to bring it back up.
Replacing the soil wholesale throws away a year of structure and soil life you paid for in patience. It’s worth it only in rare cases: a confirmed, persistent soil-borne disease, or a contamination problem a test turned up.
It is tempting to reach for a fertilizer at the same time you top up, but no guide can hand you the right amount:
How it works: Whether a soil has enough nitrogen, phosphorus and potassium (N-P-K) depends on the site, and there's no way to know it without a test.
Evidence: settled without a trial (epistemics).
We will not invent an NPK number. Your county extension office will test this soil for about $15. Until then, feed heavy feeders, do not feed root crops, and add compost.
Compost added every year covers most of what a home vegetable bed needs. Where you want to go further, correcting a real deficiency or the acidity, a soil test every two or three years tells you what the bed is short of. Then you add what it needs and nothing it doesn’t.
The bed settled; it isn’t spent. Top it up with compost every season, test it every few years, and keep the soil you spent a year improving. The next guide answers the question that usually comes right after this one: whether you still need to rotate crops in a bed you’re refreshing this way.
Good places to read more about the technique on this page. The grade on each card comes from that card’s own sources.
Next in Know your ground → The soil test, the best $15 in gardening
The rule this guide leans on → Fertilizer recommendations without a soil test are guesswork. Say so.
