I can’t remember where I first heard this recipe, but it was over a decade ago, and it’s still the best one I know of. If you’re doing lots of starts (as in hundreds), this is much more economical than buying bags of potting mix. This is what we’re using this year at the Eloheh Indigenous Center for Earth Justice.
- 1 bag Perlite, 4 square feet, preferably “propagation grade”
- 2 bags Worm Castings, 1 square foot each
- 2 blocks, Compressed Coconut Coir, only one size, I’m pretty sure. Might say, “expands to 2.5 cubic feet”
These ingredients are all appropriate for certified organic agriculture.
Coir is the main growing medium here, Perlite is for drainage, and the Worm Castings provide nutrition to the young plants. You can go with one bag of Worm Castings for plants that will spend a very short amount of time in pots before being transplanted out, like Squash (winter, summer, cukes, melons, gourds, etc.).
You can also add fertilizer to this blend. I add an organic complete organic fertilizer to batches of this I’ll be using for needy starts, like Tomatoes.
The Coir tales the place of Peat Moss, which I avoid for two reasons. First, its pH is on the acidic side, and second, it’s acquired by destroying peat bogs. We need to leave the remaining wetlands alone at this point.
You also need a tarp to mix this all on. A flat shovel, hoe, or other long-handled tool is also helpful, but not required.
Step 1: Rehydrate the Coir. I like to do it in wheel barrows, because it’s easy to tip them on to the tarp. I can’t tell you how much water I use because I just do it by feel at this point. I’m sure you can look that up somewhere, or it will be on the package (though the Coir blocks I got had no wrapping or label at all). It takes some time to rehydrate, so get this step going first, while you do other things.
Step 2: Carefully open bags so they can be reused. There’s multiple uses for them. The Worm Castings bags can hold some of your finished soil mix, in fact. I like to cut in style, with an Opinel blade, made in France. They are fine knives and very reasonably priced. No they didn’t pay me to say that. I just like them.
Step 3: Spread Perlite on tarp first. It is the lightest-weight of the ingredients, and wants to rise to the top when you mix it, so this makes the process easier.
Pro-Tip: Perlite comes in different sizes and if you’re using this soil mix in small pots for vegetable starts, get a fine grade. Sometimes they will call one “propagation grade.” If you’re using this mix in large pots, the size doesn’t matter as much.
Step 4: Dump the rehydrated Coir on top of the Perlite. When properly rehydrated, it will be soft and a little fibrousy. Not “fluffy” exactly, but much much looser than in the compressed form. Better to have too much water than not enough. Spread the Coir evenly over the Perlite.
Pro-Tip: do this whole project on ground that is slightly sloped, so that if there’s excess water in the Coir, it runs off the edge of the tarp rather than pooling in the middle. 5:
Step 5: Add the Worm Castings on top. It’s the ingredient that’s most dense, and wants to sink, so again, this makes mixing easier.
Step 6: Mix!! Long-handled tools might help at first, but the best way to mix this up is to use the tarp to “flip” the pile from one side of the tarp to the other. This step is easier with two people but can be managed by one (as I did here). Flipping it half a dozen times gets you most of the way there.
The final mix should be uniform. It doesn’t take too much effort to get there. When you’re filling pots from this mix, you might find chunks of Coir or Worm Castings that you’ll need to break up as you go.
Cover the mix. You don’t want it to dry out too much, or to get over-soaked by rain. Also, cats might appreciate this mix in a way that you don’t, so that’s another reason to cover it.