Monday, June 4, 2012

Square Foot Gardening: Mixing Your Soil


The Square Foot Gardening method uses special soil that you mix yourself. Mel's mix is made of 1/3 compost, 1/3 peat moss, and 1/3 vermiculite. This is the loveliest soil I've ever worked with - it drains well, holds moisture, and it sparkles in the sun. The ingredients can be pricey, but you can reuse it from year to year with only adding compost when you replant.

My recommendation for the soil is to not skimp. My neighbor tried SFG a few years ago, but only used a tiny amount of vermiculite because it is expensive. She didn't have very good results and abandoned her garden. If you're going to do it, I say commit to doing it right and not cutting corners with the soil. The soil is the most important part of SFG and you'll be reusing your soil from year to year so you want to get it right.


First, you need to calculate how many cubic feet of soil you'll need. To calculate cubic feet, multiply the area (# of square feet) times the depth. A 4'x4' box that is 6" deep needs 8 cubic feet of soil: 4'x4'=16sf and 16sf times 1/2 feet (6 inches) = 8 cubic feet

The ingredients for the soil come in different volumes so you'll need to do some math to make your shopping list. As I've mentioned before, given what was available in our area, it was more efficient to mix a larger amount of soil for several boxes. If you're only building one box and don't need very much soil, you can buy pre-mixed SFG soil at Home Depot or Lowes, but it is something like $13 for 2 cubic feet so this doesn't make sense if you need a lot of it.

Make your shopping list, and keep in mind that you'll probably need to go to more than one garden store to get everything. Here are some tips for each ingredient:

Compost:
Use your own or you can buy bags of compost, usually in 1 cf or 2 cf bags ranging from 75 cents to $3.00 per cubic feet. If you buy compost, buy at least five different kinds. Commercial compost is the byproduct of just one ingredient so by mixing at least five different kinds of compost, you get a richer result with more vitamins and minerals for your soil.

Peat Moss:
Peat moss comes in 3.9 cf bales, which expand to 8 cubic feet. I found 3.9cf bales of peat moss ranging from $12 to $22.

Vermiculite:
This is the most expensive ingredient, but it makes your soil loose and friable and retains moisture really well. I've found bags of vermiculite in 4cf and 6cf volumes. I noticed that the price had gone up this year from $40 for 4cf last year to $90 for 6cf this year at our local nursery. Vermiculite can be hard to find so call around before you go to save some time.

In addition to the ingredients above, you'll need a large, heavy duty tarp (16'x16'), scissors to cut open the bags, heavy duty rakes and a shovel. Mixing the soil is hard work, and you should have a helper because it gets quite heavy. You'll want to do this on a calm day. The ingredients are dusty, and if the wind picks up, it will blow your soil away.

Instructions for mixing your soil:

1. Double check your math and make sure you have the correct amounts of each ingredient. Assemble all of your ingredients and tools. Ideally, there is enough space to mix your soil next to your boxes.

2. Lay out the large tarp.

3. Begin with your bags of compost. Pour each bag onto the tarp and mix well with a rake or shovel. You can also pull up to sides of the tarp and roll the soil back and forth over itself to mix. Once the compost is blended well, add the peat moss, breaking it apart with your rake and shovel. Mix thoroughly. Add the vermiculite and mix again until all three ingredients are fully mixed. As you're mixing, be careful to not step on the soil and pack it down. You can lightly mist the ingredients with a hose as you go to keep the dust down, but don't add more water than necessary because the soil will get really heavy.

4. Add the soil to your boxes. Drag the tarp next to the boxes and fill carefully so that you don't waste any of your precious soil. Fill each box six inches deep.

5. Admire your beautiful soil. Run your hands through and imagine all of the tasty vegetables you're going to grow!

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