Homemade Soilless Potting Mix for Seedlings
- Lisa
- Oct 27
- 3 min read
If you want a no-soil seed-starting medium that drains well, holds moisture, and stays fluffy, Mel’s Mix™ from Square Foot Gardening (SFG) is a proven classic.
This guide shows you how I make a homemade soilless potting mix (Mel’s Mix) with equal parts compost, peat moss (or an SFG-approved alternative), and coarse vermiculite—measured by volume, not weight.
At a Glance
What it is: A soilless potting mix (no native/topsoil) using Mel’s Mix™ ratios
Best for: Seed starting, transplants, and raised beds
Core ratio: 1/3 blended compost + 1/3 peat moss (or approved alternative) + 1/3 coarse vermiculite (by volume) Square Foot Gardening+1
Why it works: Moisture-retentive yet well-drained, nutrient-rich from compost, light & friable for roots Square Foot Gardening
What You’ll Need to Make Homemade Soilless Potting Mix
Compost (blended)
Use a blend of different compost sources (yard, mushroom, manure-based, etc.) for a broad nutrient profile. Avoid woody, chunky, or unfinished compost. Compost is the nutrition engine of Mel’s Mix—fertilizer isn’t required when your compost quality is high.
Peat moss
Peat adds water-holding and structure. Moisten dry peat/coir before mixing to reduce dust.
Coarse vermiculite
Look for coarse grade (not fine). It improves aeration, prevents compaction, and helps manage moisture for tender roots. Square Foot Gardening
Measuring tools & setup:
A 5-gallon bucket (or any equal-size container) for measuring by volume
Tarp, wheelbarrow, or large tote for mixing
Hose or watering can (to lightly moisten peat/coir)
How to Mix Mel’s Mix (No Soil) — My Method
1) Measure by Volume
Add 1 bucket compost, 1 bucket peat (or moistened coir), 1 bucket coarse vermiculite to your mixing surface.
The “equal parts” rule is volume-based—don’t weigh ingredients.
2) Moisten & Fluff
If using peat/coir, pre-moisten until it’s evenly damp and fluffy (not soggy).
Lightly mist the pile to control dust as you mix.
3) Blend Thoroughly
Chop, fold, and rake the mix until texture is uniform—no streaks of straight peat/coir or clumps of compost.
Do the squeeze test: a handful should hold together when pressed and not drip water.
4) Fill Trays or Beds
For seed starting, fill trays, tap gently to settle (don’t compact), and water from the bottom when possible.
For raised beds, fill to depth and water in thoroughly the first time to hydrate peat/coir.
Seed-Starting Tips (with Mel’s Mix)
Depth & light: Follow the seed packet; many seeds need light to germinate.
Bottom watering: Helps avoid damping-off and keeps the surface from crusting.
Airflow: A small fan on low reduces fungal issues.
Transplant timing: Pot up when roots reach the cell edges; Mel’s Mix stays workable and light, so seedlings lift easily.
I prefer a one-mix workflow, Mel’s Mix performs well from sow to transplant when compost quality is good.
Troubleshooting
Mix feels heavy or soggy: Vermiculite too fine or peat not fluffed—add coarse vermiculite and remix.
Yellowing seedlings (after true leaves): Compost may be immature or too woody—top-dress with finished compost or repot with a better compost blend.
Hydrophobic surface (peat dry-out): Bottom-water and gently scratch the surface; add a light mulch of sifted compost.
FAQs
What is the exact Mel’s Mix ratio?
Equal parts compost, peat (or approved alternative), and coarse vermiculite—by volume, not weight.
Can I make a soilless potting mix without peat?
Yes. Research the SFG Foundation for non-peat alternatives, such as coconut coir, and how to adapt when peat isn’t available.
Do I need fertilizer with Mel’s Mix?
Not if your compost blend is high quality—the compost is the nutrient source in Mel’s Mix.
Which vermiculite grade should I buy?
Coarse vermiculite is preferred for structure and drainage.
Is Mel’s Mix truly “no soil”?
Correct—Mel’s Mix is soilless (no native garden/topsoil). That’s why it stays light, drains well, and resists compaction.
