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How to Make Soil Mix for Your Soil Blocks

Soil blocks let you germinate seeds and grow seedlings all in one spot! When you grow with seed blocks there are no seed trays, no shifting to pots, and minimal risk of transplant shock. How can you do it? Use one of our Soil Blockers to make soil cubes that stand alone. Tricia shows how simple it is to work with a Soil Blocker mechanical device in our video, Soil Blocks. You can't rely on traditional potting soil to make soil blocks -- it doesn't have the right consistency and the blocks will fall apart.

Soil Mix Ingredients

The mixture for soil blocks needs to be able to maintain a solid shape when damp.

The following recipe is from the book The New Organic Grower, by Eliot Coleman.

  • Peat moss (or a substitute) is an essential ingredient for holding water and allowing spaces for air. Don't gasp and turn away. We have peat moss that is sustainably harvested, and we carry a whole line of "coco peat" (coconut fibers) that can replace peat moss. 30 quarts is the measurement.
  • Compost for nourishment. 20 quarts
  • Sand (but you could also use vermiculite, it is sterile and holds water well), 20 quarts 
  • Oyster shell flour, 1/2 cup
  • Garden soil, 10 quarts
  • Base fertilizer-1 cup each of blood meal, colloidal phosphate, greensand
  • Mix throughly and wet with water so the mix has a consistency of wet cement. A small amount of water should ooze through the openings in the soil blockers.

Tools For Creating the Soil Mix

  • Sieve to screen all the soil mixture ingredients through a fine mesh, to have the light texture that germinating seeds need.
  • Potting tray where you can measure and dampen the soil mix.
  • Respirator to wear while working with fine powders.

Recipes for Soil Mix in Soil Blocks

Soil blocks are better known in Europe than in the U.S., so many of the recipes we have come from Great Britain. Let's start with the easy one. Quickroot seed starting mix Quickroot Let us do the soil mixing for you. We've already formulated an organic soilless seed starting mixture to use in Speedling and Plantel trays, and it works equally well with the Soil Blockers. This marvelous mixture is called Quickroot and we offer it in 1 cubic foot bags or large 54 cubic foot bags. The ingredients include coconut coir fiber, vermiculite (no detected asbestos), organic green waste compost, bone meal, and soft rock phosphate.

Peat moss based soil recipes David Tresemer, author of the Ladbrooke Soil Blocker Booklet Transplants in Soil Blocks, has a favorite recipe: 4 parts peat moss 1 part well-rotted compost 1 handful of ground calcium limestone for every cubic foot of mixture 1 handful of ground basalt rock powder Thalassa Cruso recommends: 2 parts peat moss 1 part vermiculite 1 part good garden soil (if you have that "chocolate cake" kind of friable soil) small amount of clay dust as a binder For any of these recipes or our Quickroot, moisten the soil to a slurry consistency as Tricia demonstrates in our video, then pack the Soil Blocker mechanism and you'll have your own soil blocks, ready to receive your seeds.

Are you ready to try soil blocks for your seeds this year?

9 comments

  • Lisa, if you have a large bank of weed seeds in your soil it may add some that will germinate. The recipe is from the book the New Organic Grower and he has been using the mix for years, so probably not a problem if you get a few weed sprouts growing.

    Suzanne
  • Won’t putting garden soil into the mix introduce weed seeds that will germinate?

    Lisa
  • Laura, I have updated our blog and added some measurements with a few changes. This recipe is from Eliot Coleman and can be found in his book The New Organic Grower, a great book and well worth picking up.

    Suzanne
  • When mixing the ingredients you list above, do I put in equal parts of peat moss, compost, vermiculite, and rock powder?

    Laura
  • Danielle, well that is hard to say since the quickroot is compressed when you make the blocks. I can say that it will make quite a few trays of blocks.

    Suzanne
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