Heirloom Gardener Blogs > Where the Greenfields Grow

A Do-It-Yourself Soil Blocker

Cabin fever is real, and I had it BAD this winter. To combat my restlessness, I devoted my spare time to starting my vegetable seeds indoors. I had the essentials: a heating mat, lights, seeds, and a good recipe for a seed-starting soil blend. I was almost ready to start my seeds and watch them flourish into strong, healthy seedlings, but, this year, I tried something new. I abandoned the peat pots and plastic seed trays in favor of soil blocks. In addition to leaving a smaller ecological footprint, planting seeds in soil blocks reduces shock to the roots when the seedlings are transplanted to the garden.

I shopped around online and found a reasonably priced 2-inch soil blocker, but when my seedlings started outgrowing their 2-inch blocks, I needed to upsize. I found several great options online for 4-inch blockers but found myself sticker-shocked. My only option was to build one myself (read: build one with the help of my husband). Here’s how we did it and how we would improve our next DIY soil blocker:

Supplies:

• Stainless steel sheet metal, 6x18’’
• Galvanized steel bar, at least 12’’ long, 1/8'' thick (Width determined by the diameter of the bolt)
• Bolt with a smooth round head, 7’’+
• 3 nuts & washers
• Rot-resistant, non-chemically treated plywood, at least 4’’x4’’
• 2’’x2’’x2’’ wooden cube
• 4 screws (Length determined by thickness of the plywood)
• Rivet gun and rivets (Length determined by thickness of sheet metal)

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Starting with a piece of sheet metal that is 18 inches long and 6 inches wide, bend the sheet metal, so that it forms a cube frame with approximately 4-inch wide sides. (The top and bottom are open.) 

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This should leave at least 1 inch of overlap on one side. Pop rivet the overlapping area to the cube from the inside. The frame of the soil blocker has now been created. 

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Starting with an 1/8” thick metal bar, at least 8 inches long, bend the two ends, so that they are parallel to each other and 4 inches apart. It should be able to slide down over the frame of the soil blocker.

Next, drill a hole in the center of the bar. The hole should be slightly larger than the bolt, so that the bolt can pass through the hole smoothly.

Cut an approximate 4x4 inch piece of rot-resistant plywood (not chemically green-treated) that will fit inside of the soil blocker. Note that we used a 1-inch thick piece of wood. I would recommend using at least a ½-inch thick piece of wood for strength.

Cut a 2x2x2-inch wooden cube. (This is the size of my starting soil blocks.) 

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Now that the wooden pieces are created, you need to drill a hole in the center of the 4x4 inch piece of plywood, so that the bolt can pass through. 

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Counterbore the center of the 2x2x2 inch wooden cube.

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Insert the bolt through the 4x4 inch piece of plywood, and cover the head of the bolt with the 2x2x2 inch wooden cube. Screw the two wood pieces together to capture the bolt in place. We’ll call this piece the “push plate.” (It was helpful to use a nut and washer to clamp the bolt in place on the plywood during this step.) 

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Rivet the metal bar (from steps 3-4) to the soil blocker, so that the bolt and the push plate can travel a full 4 inches from the top of the cube to the bottom of the frame once assembled.

Insert the push plate into the soil blocker frame and the bolt through the hole of the metal bar.

Use the nuts and washers to set the travel limits of the push plate, so that it will not completely slide out of the soil blocker frame.

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Extras:

• The left-over metal bar can be used to create a small handle, which is held in place by 2 nuts.
• Springs can also be added to keep the push block in an “open state” if desired.

What we learned:

• Once tightly packed into the soil blocker, the soil blend slides much more smoothly off the sheet metal than the wood. The wood needs frequent rinsing to avoid the soil sticking to the push plate. Our next DIY soil blocker would likely have a metal push plate instead of a wooden one.
• We underestimated the length of the bolt needed, so we ended up cutting the frame down from 6 inches tall to 4 inches, so that the push plate would extend clear to the bottom of the frame. For a 6-inch tall frame, we suggest a 7-inch long bolt or longer.
• We spent about 60% less on materials than what we would have spent to purchase a manufactured, store-bought 4-inch soil blocker. Our version is not perfect, but it does exactly what we intended, which is to make a big cube of dirt where my 2-inch soil blocks fit in perfectly like a three-dimensional puzzle piece, so that my seedlings have room to grow.