Soilless mixes for seed starting are a huge topic that I couldn’t even, um, dampen the surface of in one post. The important thing to remember is that, due to bacterial and fungal issues, seeds should not be started in a bunch of garden soil you go outside and dig up, assuming you can actually dig into your soil at this time of year. (If you can, and you do have really nice fluffy soil to work with, it is possible to sterilize the soil in the oven and use it, but this seems to me like one case where spending a little money saves a lot of effort and uncertainty.)
Most commercially available mixes are made of peat moss, perlite and/or vermiculite, plus fertilizer. Peat comes out of bogs; the environmental issues surrounding peat are complicated and not one-sided, but many people are now trying to avoid its use. Perlite is a volcanic glass; vermiculite is also a mineral that is altered by heating. Both help guard against soil compaction and water loss. Neither is sustainable in the long run; both take energy to turn into usable forms; both can make dust that affects the lungs.
I still use these mixes sometimes, but last year I started using instead a home-made mixture of coir fiber (from coconut husks), rice hulls, and worm castings. As I said, the environmental factors aren’t one-sided, since both agricultural products often have to be transported a long way (and I had the worm castings mailed to me, although if I had a vermicomposter they’d be created on site). The question for me is: does this mixture work? Based on last year’s results, I’d say it does, and I’m planning to do a comparison of different mixes a bit later in the season.
Here’s the process:
Coir brick (about 8″x4″x1.5″) is placed in 1.5 gallons of water and left to soak. I neglected to take a picture of the finished product, but it does give you more than 1.5 gallons of fluffy fibrous stuff.
The final mixture is about 70% coir, 20% rice hulls, and 10% worm castings (sorry, will be more scientifically precise next time). Here are the other ingredients:
One reason I chose this mix is how pleasant these materials are to work with. Rice hulls in particular make a nice sound and feel good between the fingers. They have no nutrient value, hence the worm castings: a little fertilizer for when the seedlings exhaust their own resources. (I’ll use a diluted liquid organic fertilizer later on, after transplanting to larger pots.)
Finished product looks like this:
I started a bunch of seeds with this mix today using my egg carton method, mostly flowers for my own garden, as well as leeks. More to come soon!
By the way, if you want to see what I’m talking about when I say I have a lot of seeds hanging around, I took a picture of the current stash:
About half are mine and half belong to the demo garden. Can you say seed addiction? I can.