Step 2 - Soil & Fill
A Raised Bed Soil Mix Recipe That Works
Three ingredients, simple proportions, and a per-cubic-foot table so you can order the right amounts.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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Equal parts compost, topsoil and a coarse aeration material. That is the working recipe, it is close to what most commercial bed mixes are doing, and at bulk prices it costs a fraction of buying bags.
| Component | Proportion | What it contributes |
|---|---|---|
| Compost | 1 part | Nutrition, water holding, biology |
| Topsoil or screened loam | 1 part | Mineral body, structure, trace nutrition |
| Coarse aeration material | 1 part | Air space, drainage, structure that lasts |
For the aeration component, use coarse sand, pumice, perlite, or fine bark. Avoid fine builder's sand, which fills the gaps rather than creating them and can make a mix worse.
How much you need
| Bed | Total mix | Compost | Topsoil | Aeration |
|---|---|---|---|---|
| 4 x 4 ft | 16 cu ft | 5.3 cu ft | 5.3 cu ft | 5.3 cu ft |
| 4 x 8 ft | 32 cu ft | 10.7 cu ft | 10.7 cu ft | 10.7 cu ft |
| 4 x 12 ft | 48 cu ft | 16 cu ft | 16 cu ft | 16 cu ft |
A cubic yard is 27 cubic feet, so a 4 x 8 bed at 12 inches is a little over a yard in total. Most bulk suppliers sell compost and topsoil by the yard, and a half-yard minimum is common.
Optional additions, and how much
- Worm castings -- a few pounds worked into the top few inches, or a handful per planting hole. Do not treat them as a bulk ingredient.
- Kelp or alfalfa meal -- a slow-release nutrition source; follow the rate on the bag, which is usually measured in cups per square foot.
- Biochar -- helpful for long-term structure and water holding, but it must be charged with compost or a nutrient solution first, or it will absorb nutrients out of the bed in its first season.
- Lime or sulfur -- only after a soil test tells you the pH needs adjusting. Guessing at pH adjustments causes more problems than it solves.
Mix it properly
Mix on a tarp or in a wheelbarrow rather than trying to combine layers inside the bed. Dampen the components as you go -- dry peat and dry compost both resist wetting, and a dry pocket in the middle of a bed stays dry for a surprisingly long time.
Do not over-mix. You are combining, not pulverizing; keeping some crumb structure is part of the point.
When buying bagged is the better call
For a single small bed, bagged mix probably wins. Bulk deliveries have minimum orders, you need somewhere to put the pile, and mixing 16 cubic feet by hand is a real afternoon of work. Mixing your own starts paying once you are filling two or more beds -- see the best raised bed soil for the bagged options, and the soil calculator to size the order.
What to buy
The products that fit the advice above, chosen by the process on our how we choose page. We have not hands-on tested them; specifications are the manufacturers’ own.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickCoast of Maine Castine Blend Raised Bed MixCompost-rich blend with castings, kelp and biochar | A bed you fill once and feed | 9.0 | Check price on Amazon |
| 2 |  Wiggle Worm Pure Earthworm CastingsPure castings, used at low rates | Topping up a tired bed | 8.8 | Check price on Amazon |
| 3 |  Charlie's CompostComposted poultry litter with mineral additions | A compost boost, not a fill | 8.4 | Check price on Amazon |
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Scores are our own editorial judgment, formed from published specifications and independent sources. They are not aggregated customer ratings, and they are not the result of hands-on testing, which we do not currently do. See how we choose.
Common questions
What is the best DIY raised bed soil mix?
Equal parts compost, topsoil and a coarse aeration material such as pumice, perlite or coarse sand. That gives you nutrition, mineral body and air space, which is broadly what commercial raised bed mixes are formulated to provide.
Is mixing your own raised bed soil cheaper?
Once you are filling two or more beds, considerably. Bulk compost and topsoil cost far less per cubic foot than bags. For a single small bed, bagged mix usually wins on convenience because bulk suppliers have minimum orders and the mixing is real work.
Can I use play sand in a raised bed soil mix?
Avoid it. Fine sand fills the gaps between soil particles rather than creating air space, and it can make a mix denser rather than more open. Use coarse sand, pumice, perlite or fine bark for the aeration component.
Do I need to add fertilizer to a homemade bed mix?
Not usually in the first season if the compost fraction is good -- compost carries nutrition. From the second year, either top up with compost annually or add a slow-release organic source such as kelp or alfalfa meal at the rate on the bag.
Sources
Factual claims on this page are backed by the published sources below, and product specifications are the manufacturers’ own. Where a figure is not published, we say so rather than estimating it.