By Azura · Updated June 2026 · Raised Garden Hub is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you.
Your soil is 80% of your success in a raised bed. Plants live in the top layer, so this is the one place not to cut corners. The good news: a great mix is simple.
The recipe: Mel’s Mix (and a cheaper variant)
The classic Mel’s Mix from Square Foot Gardening is three equal parts:
- ⅓ compost (ideally a blend of several sources)
- ⅓ peat moss or coco coir (moisture retention)
- ⅓ coarse vermiculite (aeration and drainage)
If vermiculite is pricey where you are, a solid budget version is 50% quality topsoil/compost, 30% aged manure or leaf mold, 20% perlite or coarse sand.
Do NOT fill a raised bed with…
- Straight garden soil — it compacts and drains poorly in a bed.
- Bagged “potting mix” alone — too light and expensive at this volume.
- Fresh manure or fresh wood chips on top — they burn roots or steal nitrogen.
How much soil do you need?
This is where people overspend. Enter your bed size to get the exact volume, bag count, and a per-third breakdown for Mel’s Mix:
Raised Bed Soil Calculator
Enter your bed size to see exactly how much soil you need.
Mel's Mix recipe (equal thirds)
- — cu ft compost / manure
- — cu ft peat moss or coco coir
- — cu ft coarse vermiculite
Top up every season
Soil settles and feeds your plants, so it drops a few inches a year. Each spring, top up with 1–2 inches of fresh compost and lightly mix it in. That alone keeps a bed productive for years without a full refill.
Save money on deep beds
For tall beds, don’t buy premium mix all the way down. Use the cheap fill methods (hugelkultur, lasagna layering) for the bottom and save the good mix for the top 8–12 inches.
Need a bed first? Start with our best raised garden beds of 2026.