The Urban Omnivore

In part one of this series I described how I built my SFG boxes and frames. In this post I’ll describe the soil that goes into those frames. The basic idea is to create your own soil mix using equal amounts of blended compost, peat moss, and coarse vermiculite. Many pre-packaged potting soils contain mixtures similar to this, however you wind up with much richer and more diverse soil if you mix your own (also, its much more gratifying to DIY). One particular reason to do the mixture yourself is that the compost available in pre-packaged potting soil mixtures is typically only from one source and doesn’t provide the diversity of nutrients necessary to grow strong, healthy vegetables.

Now for a brief word problem interlude…

I have two, 4×4 foot frames, each of which is 6 inches deep. How many cubic feet of soil will I need to fill the frames?

If your answer was 16 cubic feet, you get a gold star! Here’s how you figure it out: Each frame requires 8 cubic feet of mix to fill it (4feet * 4feet * 1/2foot = 8feet). With two frames, that’s a total of 16 cubic feet of soil. Since I have three ingredients, that technically works out to be about 2 and 2/3 cubic feet of each. I didn’t want to use a measuring cup to get the exact amounts so instead I chose to do “approximately equal” amounts and just put an emphasis on the compost. For the two frames I made sure to have 4 to 5 cubic feet each of vermiculite and peat moss and then the remaining amount would be compost.

Here’s what you’ll need to fill one Square Foot Garden with soil.

Tools:

• 1 large tarp
• 1 shovel
• 1 connected hose

Soil and frame ingredients (for each box… all measurements are approximate):

• 4 x 4 foot landscape fabric or thick black plastic
• 2.5 cubic feet of peat moss
• 2.5 cubic feet of coarse vermiculite
• 3 cubic feet of mixed compost

For ground covering and weed protection, I line all my gardens with thick black plastic available at all garden centers or as contractor garbage bags from hardware stores. You can also use landscape fabric as long as it is approved for use in a vegetable garden. I had originally purchased Pro Landscape Fabric by Dupont to use for this purpose. However, the Dupont name didn’t inspire confidence in me for my organic garden so I sent them an email inquiring about the safety of the fabric and my intended use. I received a response about a week later that read “The Dupont Landscape Fabric is not approved to be used in a vegetable garden.” Needless to say, I didn’t use it in my garden… I did use contractor garbage bags.

I got my compost and peat moss at Allandale Farm in Brookline, MA. They highly recommended Intervale Compost Complete Compost and I thought it would be a good base for my mix. The Complete Compost is made up of “leaves, sawdust, horse, chicken, and cow manure, food scraps, and melted ice cream” which definitely met my diversity requirements. For true “completeness” though, I felt it was necessary to add a few more items into the mix. To that end, I purchased some Coast of Maine Lobster Compost and Composted Manure.

The coarse vermiculite is the only difficult ingredient to acquire. Allandale Farm only carried small, 8 quart bags of vermiculite for about $8 each. That would’ve been far too expensive ($30 per cubic foot) so I called around to see if I could find larger bags. Home Depot doesn’t carry vermiculite because of concerns that it has asbestos in it. This simply isn’t the case in most commercial products today (although it certainly was in the past). In truth, there was a vermiculite mine in Montana that also happened to have asbestos in it and the vermiculite got contaminated with it. The mine closed in 1990 and vermiculite that you purchase now should not be contaminated. If you’re still concerned or paranoid about it, you can wear a dust mask while working with it (Katie and I did but mostly because all of the materials above are dusty and we didn’t want to be sneezing). I purchased Hoffman Vermiculite and did some asbestos related research on it to verify that it was safe. Hoffman Vermiculite was one of the products that had measurable amounts of asbestos in it when the EPA tested over eight years ago but Hoffman has since been working with only mines that do not contain asbestos. I still wore a mask just in case though.

Since Home Depot didn’t carry it at all, and Lowe’s only carried the smaller bags, I was getting pretty frustrated and was resigned to purchasing online, paying the shipping fees, and worst of all, waiting. Luckily, someone mentioned that Needham Garden Center wasn’t too far away and they carried 2 cubic foot bags that were only $14 each (a significant savings.) My advice to you is to check out your local farms, garden centers, and hardware stores… if they don’t have it, they might be kind enough to suggest someone who does. If all else fails, buy online.

After acquiring all of the ingredients, we need to thoroughly mix them before adding the soil to the gardens. To get a good mix, follow the steps below:

1. Place your frame where you want your garden to be
2. Line the bottom of the frame with the landscape fabric or plastic (make sure none of it is sticking out from underneath)
3. Find a large, flat area near your gardens and lay out your tarp
4. Add the different varieties of compost that you bought
5. Mix the compost with your shovel (you can get a really good mix by folding the tarp over itself a few times in different directions)
6. Add an equal amount of vermiculite to the compost (NOTE that you may want to wear your dust mask at this point). Lightly wet the vermiculite with the hose to keep the dust down. Mix thoroughly
7. Add an equal amount of peat moss to the vermiculite and compost, lightly wet, and mix thoroughly
8. Transfer your soil to your garden boxes, secure your grids, and start planting!

I’ll have one more post on an Introduction To Square Foot Gardening that will discuss the plants that we are growing this season and the trellis that we built. Throughout the growing season, I’ll post some updates on the progress of our garden and any interesting techniques or problems that arise. If you want to get started before the next post (now is the time New Englanders!) you can follow an easy rule of thumb by putting one plant per square foot (variations discussed later).

Happy gardening!