I first discovered soil blocking upon reading Eliot Coleman’s book “The New Organic Grower”. What I especially like is the fact that soil blocks can be transplanted directly into the garden. What is a soil block? Simply, a soil block is both container and growing medium and is formed by compressing the soil via the use of form. Above all, the growing medium is critical because it ensures that the ingredients are bound together when ejected from the form. Below are the benefits of using soil blocks:
- As the seedling roots in a soil block, roots will not circle around like they do in a container. Therefore, roots grow to the edges of the block and wait (unless you wait too long and the seedling outgrows the soil block). The walls formed by the block keep the roots within the block.
- Seedlings can be transplanted from the block directly into the garden and establishes quickly.
- Purchasing and storing individual containers is reduced.
- Blocks increase the long-term organic matter in the garden soil.
Components Needed
Let’s take a closer look at the two key components needed to make soil blocks: soil block maker and the blocking mix.
- Soil Block Maker is a spring-loaded ejection mold that forms a cube of soil. There are different sizes available from a ¾ inch mini-block, 1.5 inch, 2, 3 and 4 inch. In addition, there is a small button in the center of the top plate. This button leaves an impression in the soil to plant the seed. Some blockers allow for different size buttons to be inserted. For my home garden, I use a single 2-inch form with a standard size button.
- Blocking Mix is different from the soilless mixes that are generally used for seed starting. Soilless mixes are light and fluffy where the block mixes are more fibrous to withstand the consistency needed to form a block. The key ingredients in a blocking mix include:
- Sphagnum peat moss to give the block body
- Sand or perlite to provide the air needed within the block
- Compost to provide nutrition
- Fertilizer to encourage growth: blood meal (nitrogen), kelp meal (potassium) and rock phosphate (phosphorus).
View the video below to see how to make the blocking mix, how to make the soil blocks and how to plant seeds within the soil blocks.
“All life is an experiment. The more experiments you make the better.”
Ralph Waldo Emerson
Soil Block Mix Options (make vs buy)
Soil block mix can be bought or made. You can purchase soil mixes that have been formulated to have the fibrous content needed to make soil blocks. Read the label on any pre-made mix to determine whether it was formulated for making soil blocks. There are two pre-made mixes that I have used with success: (1) Vermont Compost Company Fort Vee mixture and (2) McEnroe Organic Farms Premium Organic Potting Soil. However, the challenge is finding retail outlets that carry these brands because shipping is not practical. While there are likely other brands on the market, I know these work.
A second option is to make your own mix. The recipe below has been adapted from Eliot Coleman.
Five Quart Soil Block Recipe Mix Yield: 32 2-inch soil blocks
- Three quarts of potting mix that contains Sphagnum peat moss and compost
- Perlite – Two quarts of
- Blood Meal – One-ounce
- Kelp Meal or Greensand – One-ounce
- Rock Phosphate – One-ounce
- One and a half quarts water
- 1 ten-quart bucked
First, mix all ingredients together. Next, slowly add the water, one-third at a time and mix together with your hands (gloves recommended). Mix thoroughly between each addition of water. Squeeze the mix between your hands after the second addition of water. The mixture should begin to hold together. Use your judgment on whether to add the last third of the water. The mixture should be damp and there should be no standing water within the mix. It is better to be conservative when adding the water and make a ‘test’ block to determine if the mixture is holding together.
Making and Seeding the Soil Blocks
The depth of the mix should be deeper than the soil block maker. I use a combination of a 10-quart bucket and 5-quarts of the mix because it’s easy to manage and insert the block maker.
- Fill the soil block maker with the mix by pressing the form into the mix with a twisting motion.
- Lift out and scrape off the bottom and then eject into a tray. The block should hold together if picked up with your hands.
- To seed the block, place one see per block into the small indentation that was made with the button.
- Cover the blocks with a light layer of vermiculite (to hold in moisture).
- Place the blocks in a warm area (65-75 degrees Fahrenheit) to germinate and/or on a seedling heat mat.
I thoroughly enjoy making the soil blocks and encourage you to try. For more detail on starting seedlings indoors, please reference my blog post titled “The complete guide to starting seeds indoors”. Good luck!
Insert the block maker into the blocking mix and press and twist
The blocking mix should be compact within the block maker
Press the spring loaded press to release the soil block
Soil blocks and 2-inch block maker
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