We stopped selling peat, and the plants did not notice

Peat is a wonderful growing medium. It holds nine times its weight in water, it's sterile, it's cheap, and it comes out of wetlands that took since the last ice age to accumulate at a rate of about a millimeter a year. Harvesting it releases the carbon those bogs spent forty centuries locking away.

What replaced it

Our house mix is coconut coir, composted bark fines, worm castings and pumice. Coir holds water nearly as well as peat and rewets far more easily — anyone who has watched water sheet straight off a dried-out peat pot and onto the floor knows the problem it solves. Pumice keeps the whole thing from compacting into a brick by March.

The one adjustment

Coir is not inert the way peat is: it carries potassium and can bind calcium and magnesium. That means a coir mix wants a feed with a little more cal-mag in it, which is why the fertilizer we stock alongside it is formulated that way rather than being whatever was cheapest by the pallet.

Two seasons of side-by-side trays on the shop bench, same seed lot, same light: germination within a point of each other, and the coir trays were easier to rewet after a missed weekend. We kept the trial notes if you want them.

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