Step 3 - Seed Starting
A DIY Seed Starting Mix Recipe
Three ingredients, no nutrition, and a fraction of the bagged price once you are sowing more than a tray or two.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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Two parts coir or peat, one part perlite or vermiculite, one part fine screened compost. Mix it damp, use it fresh, and add nothing else -- the deliberately low nutrition is a feature, not a gap to fill.
| Ingredient | Parts | What it does |
|---|---|---|
| Coconut coir or sphagnum peat | 2 | Holds water, holds structure, contributes nothing nutritionally |
| Perlite or vermiculite | 1 | Air space and drainage; vermiculite also holds a little more water |
| Fine screened compost | 1 | A small amount of biology and very light nutrition |
For the most reliable germination, leave the compost out entirely and use a 3:1 coir-to-perlite mix. Seeds do not need feeding, and compost is the ingredient that introduces weed seed and fungal spores.
Mixing it
- 1
Hydrate the coir first
Compressed coir blocks expand enormously -- check the ratio on the packet. Peat needs wetting too, and both repel water when fully dry, so give it time and stir.
- 2
Screen the compost
Push it through a quarter-inch sieve or a piece of hardware cloth. Lumps create air gaps around seeds and give patchy germination.
- 3
Combine by volume, not weight
Use the same container as your measure. Mix on a tarp or in a tub rather than in the trays.
- 4
Wet to a wrung-out sponge
Squeeze a handful: it should hold together and release a drop or two, not run. Fill the cells with the mix already at that moisture.
The sterility question
Bagged seed mixes are usually clean. A homemade mix containing garden compost is not, and damping-off -- the fungal collapse that kills seedlings at soil level overnight -- is the most likely consequence.
You can reduce the risk without sterilizing anything: leave the compost out, use clean trays, give the seedlings air movement, and take humidity domes off the moment seeds are up. Those habits do more than heat-treating compost in an oven, which is unpleasant and only partly effective.
Cost, honestly
One compressed coir block plus a bag of perlite makes a lot of mix -- considerably more than the equivalent spend on bagged seed starting mix. The saving only materializes at volume, though: if you sow two trays a year, buying the bag is easier and the difference is small.
For the bagged options, see the best seed starting mix. For everything else the tray needs, the best seed starting kits.
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 pickEspoma Organic Seed Starter MixFine, low-nutrient starting medium | Most seed trays | 8.9 | Check price on Amazon |
| 2 |  Jiffy Peat Pellet Seed Starter GreenhouseCompressed pellets in a domed tray | The least fuss possible | 8.0 | Check price on Amazon |
#ad We may earn a commission - prices are shown by Amazon, not by us
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 a good homemade seed starting mix?
Two parts coconut coir or peat, one part perlite or vermiculite, and one part finely screened compost. For the most reliable germination, leave the compost out and use three parts coir to one part perlite -- seeds do not need nutrition until their first true leaves.
Can you use garden soil in a homemade seed starting mix?
No. Garden soil compacts in a small cell, drains poorly and carries weed seed and fungal spores. Seedlings are highly vulnerable to damping-off, so the base of any seed mix should be coir or peat with perlite, not soil.
Is homemade seed starting mix cheaper?
At volume, considerably. One compressed coir block and a bag of perlite make far more mix than the same spend on bagged product. If you only sow a couple of trays a year, the saving is small enough that buying the bag is the easier call.
Do I need to sterilize homemade seed starting mix?
Not if you leave garden compost out of it -- coir and perlite are effectively clean. Good hygiene does more than heat treatment anyway: clean trays, air movement, and removing the humidity dome as soon as seedlings emerge.
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.