Guide
What Soil Mix for Raised Beds?
The best raised bed soil mix is 60 percent topsoil, 30 percent compost, and 10 percent aeration. Here is why each part matters, plus the per-bag amounts for a 4x8 bed.
The short answer
The best all-purpose raised bed soil mix is 60 percent topsoil, 30 percent compost, and 10 percent aeration like perlite or vermiculite, measured by volume. Topsoil gives body, compost feeds the plants, and aeration keeps the mix from packing down. Square-foot gardeners often use Mel's Mix instead.
Try it — Raised Bed Soil Calculator
Full calculatorA balanced, beginner-friendly mix. Good default for most vegetable beds.
Total soil needed
0.99cu yd
26.7 cu ft · buy ~29.3 cu ft to allow for settling
| Component | Volume | Bags |
|---|---|---|
| Topsoil | 16 cu ft | 11 × 1.5 cu ft |
| Compost | 8 cu ft | 8 × 1 cu ft |
| Aeration (perlite or vermiculite) | 2.7 cu ft | 2 × 2 cu ft |
A raised bed is not one bag of "soil." It is three ingredients in the right ratio.
Get that ratio right and the bed drains well, feeds your plants, and stays loose for years. Get it wrong, with straight topsoil or pure potting mix, and you fight compaction or empty your wallet.
This guide covers the mix itself. For the total volume math, the how much soil for a raised bed guide walks the formula, and the broader raised bed soil hub covers depth and cost.
The best mix: 60/30/10, and what each part does
The default vegetable blend is 60 percent topsoil, 30 percent compost, 10 percent aeration, all by volume. Each part has one job.
- Topsoil (60%) is the body. It gives the bed mineral structure and bulk, the stuff roots anchor into.
- Compost (30%) is the food. It adds organic matter, nutrients, and the biology that holds moisture and feeds plants.
- Aeration (10%) is the breathing room. Perlite or vermiculite keeps the mix from packing into a dense brick.
That balance is exactly why this blend works. Per the UMass Amherst Extension guide to raised bed soils, a raised bed needs both mineral soil and organic matter, not one without the other.
Compost is the part most people skimp on. Lean toward 30 percent, not 10.
The 60/30/10 ratio for a 4x8 bed
Ratios are easy to nod at and hard to shop for. So here is the split in actual bags.
A 4x8-foot bed filled 10 inches deep holds about 26.7 cubic feet of mix. Break that into three stacks by the 60/30/10 ratio.
| Ingredient | Share | Cubic feet | Bag size | Bags |
|---|---|---|---|---|
| Topsoil | 60% | 16.0 cu ft | 1.5 cu ft | 11 |
| Compost | 30% | 8.0 cu ft | 1.0 cu ft | 8 |
| Aeration (perlite/vermiculite) | 10% | 2.67 cu ft | 2.0 cu ft | 2 |
So one 4x8 bed is 11 bags of topsoil, 8 bags of compost, and 2 bags of aeration. That is the cart, not a vague "one cubic yard" you sort out at the register.
The Raised-Bed Soil Calculator rebuilds this list for any bed size and depth, so you do not redo the math for a 3x6 or a 4x10.
Mel's Mix: the square-foot alternative
The other recipe you will see is Mel's Mix, from Square Foot Gardening. It is equal thirds by volume.
- One-third compost (blend several kinds if you can)
- One-third peat moss or coco coir
- One-third coarse vermiculite
Per the Square Foot Gardening Foundation, the point is a light, friable medium that drains fast and resists compaction, ideal for tight, intensive planting.
The trade-off is cost. Mel's Mix uses no native topsoil, so filling a deep bed with it runs pricier than the 60/30/10 blend.
Pro tip
Pick by depth and budget. For a standard 8 to 12 inch vegetable bed, the 60/30/10 blend is cheaper and holds moisture well. For a shallow square-foot grid where fast drainage matters most, Mel's Mix earns its higher price.
What to avoid: straight topsoil or pure potting mix
The two easy shortcuts both backfire. A raised bed behaves like a big container, not like the open ground.
Fill it with straight topsoil and it compacts. Per the University of Maryland Extension, topsoil belongs in a raised bed mixed with compost, not used alone, because dense soil cuts drainage and stalls roots.
Fill it with pure potting mix and you overpay for the wrong thing. Potting mix is built for small pots, so it is too light to give a full bed lasting structure and far too expensive to fill one.
Bagged garden soil has the same problem as topsoil. It is meant to amend in-ground beds, so on its own it packs down in a raised bed.
How much to buy, plus 10 percent for settling
Buy the bag list above, then add a little. Fresh mix drops after the first few waterings as it settles.
Plan for about 10 percent extra. On the 4x8 bed that takes 26.7 cubic feet up to roughly 29.3 cubic feet, so fill a touch high and top up after the bed beds in.
Need the compost figure on its own? The how much compost do I need guide sizes just that ingredient.
Common mistake
Do not buy three bags labeled "raised bed soil" and call it done. Those premixes vary widely, and many are mostly bark or compost with little mineral body. Check the ratio. A bed wants real topsoil for structure, not just dark, fluffy organic matter that shrinks by half in a season.
The mix comes down to one ratio and three bags. Sixty percent topsoil for body, 30 percent compost for food, 10 percent aeration to keep it loose, plus 10 percent more for settling. Build that and the bed works the first year and the fifth.
Got your bed size? Open the Raised-Bed Soil Calculator for your exact per-ingredient bag list.
Common questions
What is the best soil mix for raised beds?
A balanced all-purpose mix is 60 percent topsoil, 30 percent compost, and 10 percent aeration like perlite or vermiculite, by volume. Topsoil gives body, compost feeds the plants, and aeration keeps the bed from packing down. Square-foot gardeners often use Mel's Mix, which is equal thirds of compost, peat or coir, and coarse vermiculite.
What is the difference between garden soil and raised bed mix?
Bagged garden soil is meant to amend in-ground beds, so it is denser and can compact in a raised bed. A raised bed mix is lighter and more open, so it drains well but still holds moisture. A raised bed behaves like a big container, so it needs the looser blend.
Can I fill a raised bed with just topsoil?
No. Straight topsoil compacts in a raised bed because the bed acts like a container, which cuts drainage and root growth. Topsoil needs compost for nutrients and an aeration material to stay loose. Per University of Maryland Extension, mix topsoil with compost rather than using it alone.
Is potting mix good for raised beds?
Not by itself. Potting mix is built for containers, so it is too light to give a full bed lasting structure and too expensive to fill one. Use it only in small pots. For a raised bed, build the 60/30/10 blend or Mel's Mix instead.
How much of each ingredient do I need for a 4x8 bed?
A 4x8 bed filled 10 inches deep needs about 26.7 cubic feet of mix. Split 60/30/10, that is roughly 11 bags of topsoil (1.5 cu ft), 8 bags of compost (1 cu ft), and 2 bags of aeration (2 cu ft). Add 10 percent for settling.
Sources
Agronomic claims in this guide are checked against these primary sources.
- Growing Vegetables in Raised Beds — University of Maryland Extension
- Raised Bed Soils for Vegetable Gardening — UMass Amherst Extension
- The Magic of Mel's Mix Soil — Square Foot Gardening Foundation
Keep reading
How Much Soil for a Raised Bed?
Length times width times height in feet, divided by 27, gives cubic yards. A 4x8 bed at 10 inches needs about 1 cubic yard. Formula, bag list, and a calculator.
Read →How Much Compost Do I Need?
Multiply square feet by depth in inches, divide by 324 for cubic yards of compost. Formula, worked examples, and a bagged-vs-bulk guide.
Read →Raised Bed Soil: The Complete Guide (Mix, Depth, Cost)
Everything that goes in a raised bed, in one place: the fill formula, the 60/30/10 mix, how deep to build, a cheaper bottom layer, and bulk-vs-bagged cost.
Read →