Note: We strongly recommend a triple-high Instagarden for heated and insulated gardens, to make it unlikely that you will accidentally break the electric heater when digging in your garden.
Difficulty level: difficult
(1) Cutting the insulation will create a small ecological disaster. You can make this project easier by cutting the insulation with a saw, but that will create a large ecological disaster.
(2) Most people will have at least one serious moment of frustration trying to evenly distribute the heating cable on the hardware cloth.
You should plan on three to five hours to complete this project.
Small putty knife
Heavy Duty Scissors, Garden Shears, or similar
Closed cell insulation, 2 inches thick, R=10 (pink or blue), 8 'x 4' for hexagon and 4' x 4' for square.
Pea Gravel, 1 to 5 cubic feet
Plastic hardware cloth, 1” mesh preferred, enough to cover the bottom of your Instagarden
Heating cable(s) with thermostat, Grow-Kwik brand
-two (2) 48' cables for a hexagon
-one (1) 36' cable for a square
small zip ties (100)
twist ties (50)
(1) Cut the insulation into pieces, so that your Instagarden can drain.
(1a) For a square raised bed garden, draw four squares on the sheet of insulation, each 17 1/2" x 17 1/2". Score the insulation with the utility knife along the lines, then snap off each square. Trim the insulation pieces with the utility knife, and clean up any excess insulation with the shop vacuum.
(1b) For a hexagon raised bed garden, mark a straight line from one end of the insulation to the other end, 31 inches from one of the long edges. Use the marker and straightedge to draw five rectangles, each 18 inches wide and 31 inches long, and then divide each rectangle into two triangles. Turn the insulation over and draw the exact same pattern on the other side, so that each line drawn is identical to the line on the other side.
Score all the lines as deeply as possible using the utility knife. Score the lines on both sides of the insulation sheet. Snap the sheet of insulation into two rectangles, the wider one covered with triangles. Snap apart all the triangles. Use the utility knife to clean up any edges that didn’t snap properly, but don’t be too fussy. Clean up any excess insulation with the shop vacuum.
Take one of the triangle shaped pieces of insulation and use it as a pattern to draw two triangles on the remaining large piece of insulation. Draw two triangles on the opposite side so that they correspond to the triangles on the other side. Score the lines on both sides using the utility knife, then snap the triangles apart. Use the putty knife to break pieces apart. Trim as necessary. Vacuum up insulation pieces.
(2) Make the pattern for the heater.
Lay the plastic hardware cloth in the bottom of your Instagarden and cut to size using heavy-duty scissors (do not use the utility knife!). If you need to use more than one piece of plastic hardware cloth, connect them with several zip ties. Remove the hardware cloth from your Instagarden.
(3) Lay out the heating wire(s) on the pattern. This is the difficult part. Place the hardware cloth in a comfortable place and start laying out the heating wire. For a hexagon heater you will lay out two loops, with the cords next to each other. You will need the wire to be three to four inches away from other sections of the wire, without the wire crossing or touching, and with no wire left over. Use the twist ties to secure the wire to the hardware cloth and change your layout as necessary so that the wire is evenly distributed over the hardware cloth. When your design is complete, use zip ties to secure the wire to the hardware cloth.
(4) Place landscape fabric on the bottom of your Instagarden to prevent tree roots from infiltrating your garden. Place the landscape fabric down first, then put your Instagarden raised bed garden on top of the landscape fabric. Secure the landscape fabric with staples.
(5) Put an inch to an inch and a half of pea gravel on top of the landscape fabric and arrange evenly. Use three (3) cubic feet for a hexagon and one (1) cubic foot for a square.
(6) Arrange the insulation on the pea gravel so that all drainage gaps are equal and then cover the insulation with another inch of pea gravel.
(7) Place your heater on the pea gravel, with the heater side toward the ground and the hardware cloth side on top.
(8) Cover with soil and plug it in! Make sure you plug into a ground fault interrupt (GFI) outlet.