How it works
total = length × width × depth; each part = total ÷ 3
Mel’s Mix, from Square Foot Gardening, is one-third blended compost, one-third peat moss (or coco coir) and one-third coarse vermiculite — measured by volume, not by weight. The calculator finds the bed volume by multiplying length, width and depth in feet, then divides by three to size each ingredient. It also converts each third into five-gallon buckets: a five-gallon bucket holds about 0.67 cubic foot, so the standard 4-by-4-by-6-inch bed — eight cubic feet — works out to roughly four buckets of each ingredient, matching the published recipe. The compost is the most important third: it should be a blend from several sources — at least three, ideally five different composts — so the bed gets a broad range of nutrients rather than relying on one input.
Sources
- Square Foot Gardening Foundation — Mel’s Mix Resources Mel’s Mix is 1/3 blended compost, 1/3 peat moss (or coco coir) and 1/3 coarse vermiculite by volume; a 4×4×6-in bed needs 8 cu ft — four 5-gallon buckets of each.
- Square Foot Gardening Foundation — The Magic of Mel’s Mix The three ingredients are used in equal parts; blended compost should have at least 3 but ideally 5 different ingredients for balanced nutrition.
FAQ
What is Mel’s Mix?
Mel’s Mix is the soil recipe from Mel Bartholomew’s Square Foot Gardening method: equal parts, by volume, of blended compost, peat moss (or coco coir) and coarse vermiculite. It is light, holds moisture without waterlogging, and is nutrient-rich, so plants can be spaced closely in shallow beds.
How much of each ingredient do I need?
Exactly one-third of the total volume each. For the classic 4-by-4-foot bed, six inches deep, that is eight cubic feet total — so about 2.7 cubic feet, or roughly four five-gallon buckets, each of compost, peat and vermiculite. Enter your own bed size above and the calculator does the split.
Can I use coco coir instead of peat moss?
Yes. Coco coir is a common, more renewable substitute for peat moss and is used in the same one-third proportion by volume. Peat is acidic and mined from bogs, so many gardeners prefer coir on sustainability grounds; either works in Mel’s Mix.
Why does the compost need to come from several sources?
Square Foot Gardening recommends blended compost made from at least three, and ideally five, different sources — for example composted manure, mushroom compost and homemade compost. Different composts carry different nutrients, so blending them gives the bed a broader, more balanced supply than any single compost.
Do I have to replace Mel’s Mix every year?
No. The peat and vermiculite last for years; only the compost is consumed as plants grow. Each time you replant a square, mix in a trowel of fresh compost. Top the bed back up with compost annually rather than remaking the whole mix.
How deep should a Square Foot Gardening bed be?
The standard Square Foot Gardening box is six inches deep, which suits most vegetables because the loose, rich mix lets roots spread rather than dig. Deep-rooted crops like tomatoes do better with a deeper box or open ground beneath the bed.
Volumes are estimates and the mix settles after watering, so prepare a little extra. Ingredient quality — especially the compost blend — drives results. General gardening guidance, not professional advice.