Home › Soil and water

Raised Bed Soil Mix: How to Fill a Raised Bed Cheaply (Ratios and Volumes)

Ratios, bag counts per bed size, and the log trick that halves the cost of a deep bed.

Updated 2026-09-10

This guide contains affiliate links. If you buy through them I may earn a commission at no extra cost to you.

The mix

60% topsoil or bagged garden soil, 30% compost (mix two sources), 10% aeration (perlite, coarse bark fines or coir). Pure compost or pure bagged potting mix both fail: one slumps and stays wet, the other dries out and blows away.

How much you need

Bed	12 in deep	17 in deep
4×4 ft	0.6 cu yd (16 bags of 1 cu ft)	0.85 cu yd (23 bags)
4×8 ft	1.2 cu yd (32 bags)	1.7 cu yd (45 bags)
2×8 ft	0.6 cu yd (16 bags)	0.85 cu yd (23 bags)

Bulk delivery of a screened “garden blend” by the yard costs half of bagged soil once you need more than about 1 cu yd.

The deep-bed trick

In a 17 in bed, fill the bottom 6–8 in with logs, branches, leaves and grass clippings, water it, then add the mix on top. It saves a third of the soil cost, holds moisture and settles a couple of inches over the first year: top up with compost.

Each spring

Add 1–2 in of compost on top. Do not dig it in. Test pH every couple of years (6.0–7.0 is right for almost everything). Feed heavy feeders (tomatoes, squash, brassicas) with an organic slow-release fertilizer mid-season.

What I'd buy first

Luster Leaf Rapitest Soil Test Kit

around $15

Cheap pH/NPK check before you buy amendments.

Check price via Amazon Associates (US)

Espoma Organic Garden-tone Fertilizer 4 lb