Best Soil Mix for Raised Beds: The 60/30/10 Recipe Explained
A raised bed is only as good as what goes into it. The 60/30/10 recipe — 60% topsoil, 30% compost, 10% aeration — is the mix experienced growers keep coming back to. Here is what each part does, how much you need for the most common bed sizes, and the mistakes that ruin an otherwise good mix.
Fill raised beds with about 60% topsoil, 30% compost, and 10% aeration material such as perlite or rice hulls. For a standard 4 × 8 ft bed filled 12 inches deep (32 cubic feet), that works out at roughly 19 cubic feet of topsoil, 10 of compost, and 3 of aeration. Keep compost at 30% or below — richer is not better.
What the 60/30/10 ratio actually means
The numbers are percentages by volume, not weight: six buckets of topsoil, three of compost, one of aeration, in whatever bucket you like. Volume is what matters, because roots experience space, not weight.
It is a starting recipe, not a law of nature. Filling over sandy ground? Lean slightly towards more compost. A heavy clay base underneath? A touch more aeration helps drainage. But if you are filling beds for the first time, mix it as written — it lands in the sweet spot for drainage, fertility, and structure that university extension guidance keeps confirming.
What each ingredient does
| Ingredient | Share | Job it does | What to buy |
|---|---|---|---|
| Topsoil | 60% | Structure and minerals — the bulk that roots push through | Screened loam topsoil; bulk is cheapest |
| Compost | 30% | Nutrients, microbes, and water retention | Aged, finished compost — dark, crumbly, earthy-smelling |
| Aeration | 10% | Drainage and the air pockets roots breathe through | Coarse perlite, pumice, or rice hulls |
Why cap the compost at 30%? Extension services generally advise keeping compost to about a third of a raised-bed mix at most. Go beyond that and the mix keeps decomposing and shrinking, excess salts and phosphorus build up, and the bed holds too much water in spring and slumps by autumn.
How much of each for your bed
Work out your bed’s total volume first (length × width × depth), then split it 60/30/10. Bag counts assume standard 2 cu ft bags, rounded up:
| Bed size | Total volume | Topsoil (60%) | Compost (30%) | Aeration (10%) |
|---|---|---|---|---|
| 4 × 4 ft, 12 in deep | 16 cu ft | 9.6 cu ft (5 bags) | 4.8 cu ft (3 bags) | 1.6 cu ft (1 bag) |
| 3 × 6 ft, 12 in deep | 18 cu ft | 10.8 cu ft (6 bags) | 5.4 cu ft (3 bags) | 1.8 cu ft (1 bag) |
| 4 × 8 ft, 6 in deep | 16 cu ft | 9.6 cu ft (5 bags) | 4.8 cu ft (3 bags) | 1.6 cu ft (1 bag) |
| 4 × 8 ft, 12 in deep | 32 cu ft | 19.2 cu ft (10 bags) | 9.6 cu ft (5 bags) | 3.2 cu ft (2 bags) |
| 4 × 8 ft, 18 in deep | 48 cu ft | 28.8 cu ft (15 bags) | 14.4 cu ft (8 bags) | 4.8 cu ft (3 bags) |
Skip the arithmetic — get your exact mix
Enter your bed’s dimensions for cubic feet, cubic yards, bag counts, and the 60/30/10 split worked out for you.
How to mix it: the layer method
You do not need a cement mixer. Add the ingredients in layers — a few inches of topsoil, a thinner blanket of compost, a sprinkle of perlite — watering each layer as you go. Repeat until the bed is full, then fork the top 8 inches together to blend it. Watering between layers settles air pockets now, rather than after you have planted.
Fill to about 1–2 inches below the rim. Fresh mix settles several inches over the first few weeks, so top it up with compost before planting — and plan on a 1–2 inch compost top-dress every spring to replace what decomposes.
What not to put in a raised bed
- Pure topsoil — compacts into a brick without organic matter and aeration to open it up.
- Pure compost — shrinks dramatically as it keeps breaking down, runs too rich, and drains poorly on its own.
- Unamended soil dug from the garden — brings weed seeds, compaction, and whatever pH problems you were trying to escape.
- Fresh manure — burns roots and can carry pathogens. Compost it for 6–12 months first.
- A gravel “drainage layer” at the bottom — it does not improve drainage; water actually moves more slowly across the texture boundary, and you lose root depth.
- Dyed or painted wood chips mixed through the soil — fine as a surface mulch, not as a mix ingredient.
Bagged mix vs mixing your own
Pre-mixed “raised bed mix” in bags is essentially this recipe, ready to pour — you pay for the convenience. Buying the three components separately and mixing them costs less per cubic foot, especially if you can get topsoil and compost in bulk by the cubic yard. The break-even point is usually around one cubic yard (27 cubic feet): below that, bags are simpler; above it, bulk delivery wins on price and on plastic waste.
Either way, check the label on bagged topsoil — some of it is little more than shredded wood and sand. Good bagged topsoil feels loamy and names its source.
Frequently asked questions
Can I use 100% compost in a raised bed?
It is tempting, but no. Straight compost keeps decomposing and shrinking, so the level drops fast; it can also carry excess salts and phosphorus that lock out other nutrients. Extension guidance consistently caps compost at about a third of the mix.
Can I reuse last year’s raised bed soil?
Absolutely — good soil improves with age. Each spring, top up what has settled with 1–2 inches of fresh compost and fork it into the top few inches. A full replacement is rarely needed.
What pH should raised bed soil be?
Most vegetables are happiest between pH 6.0 and 7.0 — the standard extension recommendation. An inexpensive test kit is fine for a first check; retest every couple of years, especially if you add a lot of compost or manure.
Perlite, vermiculite, or rice hulls?
All three aerate. Perlite is the classic choice for drainage and does not break down. Vermiculite holds more water — better for thirsty crops in hot climates. Rice hulls are the budget, renewable option, but they decompose within a season or two, so top them up annually.
Do I need fertiliser as well as compost?
In year one, a good 60/30/10 mix usually carries crops through the season. From year two, feed hungry crops (tomatoes, squash, brassicas) with a balanced fertiliser or regular compost top-dressing, following label rates.
How deep should the mix go?
Twelve inches suits most vegetables. Salad leaves and herbs manage with 6–8 inches; carrots and parsnips want 12–18. For deep beds, fill the bottom with cheaper bulk topsoil and put the 60/30/10 mix in the top 12 inches where the roots are.
Related guides
How Much Soil Do I Need for a Raised Bed?
The 30-second volume formula plus ready-made tables for every common bed size.
How to Grow Tomatoes in a Raised Bed
Spacing, planting depth, watering, and feeding — the complete tomato playbook.
How Often Should I Water My Vegetable Garden?
The 1-inch rule, the gallon math for your bed, and schedules by soil type.
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