Wednesday, April 24, 2013

DIY Square Foot Garden (SFG): Making Soil and Planting Seeds

Bruce Filling Raised Bed with Soil Components
Bruce in Action

Instructions by Bruce

Once you have a raised bed built for your square foot garden (details in Sunday’s post,) you’re ready to fill it with soil, make the square foot grid sections, and plant your seeds. You can also build a hoop house to protect small plants from cold temperatures; I will give hoop house instructions in my next post. All New Square Foot Gardening, the latest and greatest book by SFG pioneer Mel Bartholomew, recommends soil made from equal parts of peat moss, vermiculite, and organic compost from several sources. Vermiculite holds moisture and reduces the amount of watering necessary. But there is considerable debate about it due to its high cost and sustainability (it’s mined). Bruce reduced the amount of vermiculite in the mix. He noted that a high quality compost mixture also holds substantial water as well as loosening the soil—vermiculite’s other soil-building contribution. Bruce replaced the classic SFG wooden grid with a woven grid of nylon twine secured by wood screws, both of which we had on hand. Without a grid, as Mel Bartholomew points out, it’s not a square foot garden.

Peat Moss Being Added to Bed
Making the SFG Soil
As far as plants, anything goes, according to Bruce’s research, and mixing it up is part of the fun and science (ideally you’ll rotate crop placement each year to maximize fertility). Observe the plant spacing instructions on each seed package. If the package says to space 4” apart, three plants will fit in a square foot, if 6” apart, two plants, if 12” apart, just one plant. Some seeds, like lettuce and braising greens, can be sown close together and thinned out as they grow. The thinned baby plants can be added to salads. Bruce placed all of our peas and beans in the back row, where we plan to add a trellis or add bean poles when plants get bigger.

Notebook with Diagram of Raised Bed
Keeping Track of What's Planted Where
One last word about planting: be sure to make a chart of which seeds are planted in each grid section. You might think you’ll remember without a diagram, but you don’t want to be confused if some seeds don’t come up. You could accidentally replant a duplicate of something you’re not crazy about, while skipping your favorite. Marking the sections themselves seems like a good idea, yet markers can disintegrate or become illegible, and sometimes mysteriously disappear or get buried (personally I blame squirrels). It’s best practice to back up any onsite markings with a diagram.

Square Foot Garden: Soil, Grid, and Plants

Materials & Tools:
7.5 cubic feet quality organic compost
6 cubic feet peat moss
22 quarts (2 small bags) vermiculite
Landscaping rake or small shovel
Yardstick or tape measure
Pencil or scribe
Screwdriver bit for drill
12 – ½-inch #6 wood screws
~40 feet nylon twine

Screw with Twine Wrapped Around it
Allow Space to Wrap or Tie Nylon Twine
Making the Grid Framework:
With yardstick or measuring tape and pencil or scribe, mark off 1-foot increments on the top edge of one side of the raised bed. Starting one foot from corners, use drill to screw wood screws into the center of each mark. Don’t tighten screws down flush, leave a small space to tie the twine around. Mark other sides of the raised bed and add screws.

Adding optional Hoop House Hardware:
Now is the most convenient time to add the hoop house hardware, before making the grid. Alternatively, you could add it after making the grid and even after planting. Hoop house instructions in Friday’s post.

Making the Soil:
Instead of the standard SFG practice of mixing the soil on a tarp (and getting the tarp all gritty), Bruce mixed it up directly in the raised bed. He added compost first, followed by vermiculite, and peat moss on the top. Then he used the flat side of the rake to mix it together. You might prefer a shovel. Using the tine side of the rake runs the risk of snagging and breaking the gopher wire. Mix soil components together well, then level out.

Screw with Two Knots on it
Tie Both Ends of Twine to Same Screw
Making the Grid:
Start stringing nylon twine on shorter sides of bed. This means you’ll be making the longer dimension of the (twine) grid first. It’s easiest and strongest to double the twine: tie twine to one screw, stretch twine tightly across bed around screw on opposite side, then bring twine back to original screw, pull tight and tie securely. Cut twine and proceed to adjacent screw, completing the short sides of the bed first.

Diagram of Warp and Weft
The Basics of Weaving
Next you’ll string shorter pieces of twine from the longer sides of the bed. The key to a good grid is that it’s woven to form an integrated unit. The twine that is already in place is, in weaver’s terms, the warp (lengthwise) twine. The shorter pieces you will now add are the weft. See illustration for basic weaving technique: essentially the weft strands alternate over and under the warp.

Warp and Weft Woven
"Trapping" Warp with Weft
Use the same technique of doubling the twine on the weft as you did on the warp: tie one end to a screw, weave through warp twine, and wrap around opposite screw. Then weave back through warp (alternating passing weft twine over and under warp twine) to the original screw, “trapping” warp twine with weft, (see photo), stretch weft twine tight and tie off. Proceed from one end of board to the other, until you have a woven network, which is your planting grid. Each section is one square foot.

Planting the SFG:
Water the bed well and let it drain. Make sure it’s moist. Meanwhile, make a diagram of your bed and its grid and label each section with what you will plant. You might want to start with short plants in front: lettuces and other greens, and tall climbing plants like beans in the back row where you can prop up stakes during the season.

Check the seed packages for recommended plant spacing and planting depth. Follow these instructions for each seed. Note that if recommended spacing is 12 inches, you’ll only one plant will occupy that section; if it’s 6 inches, two plants will go in the section, etc. Make a note of the germination time for each seed variety from its package. Lastly, make a note of the date you planted the garden.

Classic planting technique calls for 2 seeds to be planted in each hole, in case one seed doesn’t sprout. This means you’ll have to pinch off the weaker plant as the plants start to grow. It’s hard for some people (including yours truly) to kill off a seedling like this, so if you prefer, plant one seed to each hole. You can always replant a section if no seedlings come up. In fact, double planting is not a guarantee that all sections will germinate (especially if temperatures get low), and replanting one or more sections isn’t unusual. Replant a section if the plants don’t come up during the germination time listed on their package.

Water the beds again after planting. More tips on watering and temperature control, including hoop house construction, in Friday’s post!


  1. My little raised bed garden is 4' x 4'. I never thought to mark off the grid. Great idea! I'll definitely be doing that this year -- and good reminder to mark it all down in a notebook, too. You're right, the markers go missing very quickly.

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