It's time to start tender seedlings inside, to be set out in the garden after Memorial Day. But I was out of my seed starter mix, so today I made up a batch. Regular potting soil is too coarse, and doesn't hold enough water to get seedlings off to a good start. Curious, I looked at the tiny bags of seed starter mix in my local home improvement store. Not only would buying enough for my needs be prohibitively expensive, but I really don't think using something that, in reading the small print on the back, cautions that it's important to wear gloves while using this product, keep it away from children, and write to them to find out more about the metals (metal??) it contains. That just sounds chemical-laden to me. I'll continue to mix up my own, thank you.
Seed Starter Mix
3 parts compost
3 parts sphagnum peat moss (or coir fiber)
1 part vermiculite (or perlite)
a dusting of fertilizer booster blend (equal parts bonemeal, bloodmeal, & greensand)
I bought a bale of compressed peat moss at Wal-Mart, and big bag of vermiculite at Home Depot. Both are enough to last me for another 5-6 years of planting seasons. The compost and fertilizer blend I already had.
My compost is completely cooked, but still pretty coarse, so I had Aries run me a bin-ful through the chipper/shredder. Better, but still too coarse for little broccoli seeds. But once I sifted everything though a riddle, I had a wonderfully fluffy, fine-textured mix. It was easy to mix everything together with a trowel.
It's important to get the mix evenly damp before planting. The moss holds water well, but once it dries out, it's hard to get the moss re-hydrated again without disturbing the seeds. Wheeling it over to the faucet, I ran enough water into the wheelbarrow to make a soupy mess, and left it for a few minutes. When I came back, the moss had soaked up everything but there were still dry spots underneath. I kept adding water, stirring with a short-handled shovel, and waiting a bit, until everything was evenly damp.
Using compost, I probably won't have any pathogens or molds in this mix, but just to be on the safe side I solar-sterilized it. An old salvaged storm window was the perfect size to fit over the wheelbarrow. Weighting the glass down snug, with an old rug and a wadded-up feed bag tucked into the spaces top and bottom, I left the whole thing sitting in the sun all afternoon. Despite the somewhat cool temperatures today, the glass started steaming up almost immediately. This evening, I'll fill up my seed starter bin and bring it into the house so it doesn't freeze overnight. And tomorrow, I can plant my seeds!