January 27, 2012

Making Potting Soil

As I began to plan for the garden, and read through the blogs and pages that share great ideas, I realized that dirt was going to be a big problem.  Specifically, I've been looking into planting potatoes because I see great tutorials for ways to do so in a container (such as this one in the Seattle Times) and because I see that know that it's one of the easiest to grow from farmer's market potatoes.  However, they require a ton of dirt and need to be started in potting soil (and I know hydroponics is an option, but I don't know much about it.  So, until I have time to read more about it, I'm going to focus on the soil).

(see some ways to make potting soil after the jump)

Potting soil is expensive, and a bag will take me over my $5 limit. Since I don't want to spend money on dirt, I have to find ways to get soil. Unfortunately, a search brought up alternatives that were over $5 (like these at Progressive Gardening), or thinly veiled advertisements for a particular brand of better-than-potting soil. eHow provides a recipe for DIY potting soil that involves "combining. . .peat and compost" (here) which requires buying peat. Then there were recipes at the Artistic Garden website (here), which involved buying materials. . .also, not an option. sigh.

Eventually, I found what I was looking for at plantcare.com.  They provided a recipe that was flexible enough that I could substitute some of the items that cost money for items that didn't.  Their full article is here.  They explain that commercial potting soil typically has the following in it:
  • Dirt or mud. (I can totally get that!)
  • Organic matter – like peat moss, compost, worm castings, ground bark. (ok, peat moss costs, but compost doesn't.  So I can get that!)
  • Vermiculite – silicate material for air space and drainage. (Later in the article, they mention sand or bark as viable alternatives for this. . .I can get that, too)
  • Perlite – volcanic material, lightweight provision for air and drainage. (because this serves the same purpose as vermiculite, my sand/bark will do here too).
  • Fertilizer – typically slow release for extended benefit. (not sure what to do about this, so I'm skipping it for now)
I'm going to go with 30/30/30 dirt/compost/bark or sand.  We'll see how it does.

I came across 3 reasons to use potting soil instead of regular garden dirt: it is more porous, it is sterile, it fertilizes the plants.  So, I will make a mixture of soil, organic matter, and air-space/drainage material (aka sawdust/ground bark).  That takes care of the first reason.  Fortunately, both Mother Earth News (see below) and Artistic Garden explain how to sterilize potting soil.  Artistic Garden suggests "Place soil in a shallow pan with a raw potato in the center. Bake in the oven until the potato is thoroughly cooked" as a completely do-able solution.  That covers the second, and I'll just tackle the third as I go along.

Mother Earth News has an even more detailed explanation of how to make your own potting soil (here).  Their creation is much more elaborate, involving compost screens and solar cookers, but they do a nice job of explaining why you have to be careful with the potting soil you use for seedlings, saying "When you have excellent-quality, cured compost, and you’re not working with light-stressed little seedlings (the most disease-prone of all green beings), it’s fine to go ahead and mix up a 50:50 mixture of compost and good soil."  But since I'm working with wee plants, I need to do something safer.  Fortunately, they're right there with the suggestion to basically cook moistened soil in the oven at 200, tossing it into a casserole dish and shutting off the oven when the soil hits 150 degrees, then letting it sit in there for a half hour.  Ok, their explanation was more complex, detailed and articulate, but I'm all about easy in this case.

The first hurdle in this process is getting compost.  Due to my husband's distaste for dirt/bugs/rotting things, we don't compost. . .and really, who can blame him.  Who can blame him?  Having a compost heap is odd to non gardeners because it's basically keeping the things you would normally throw away and letting them rot. Still, if I took great care of it I think I could make this work.  I suspect that now that we have garage space, I could probably start a decent little compost bin out there that would be "clean" enough to pass muster.

eHow Home warns against using compost-based soil, saying "locally obtained compost often contains lots of contaminants. . .so you should avoid using it for growing fruits and vegetables." I wonder what contaminants they're talking about?  I suppose pesticide and fertilizer, but if I use my own compost, or know the source of the compost I get then that would take care of those issues.  I need to look at that further.

In the meantime, I'm going to get my butt in gear on starting to compost. . .and  for now in finding places to collect other people's compost because it's waaaaay to late to start now for compost for next month.

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