Use soil blocking to skip plastic pots and develop stronger seedlings.
When beginning seeds indoors, skip single-use plastic pots and instead use a method called soil blocking. Not only is it a waste-saver, but soil blocking creates healthier seedlings that don’t become root-bound. Here’s how to make and utilize your own soil blocks for starting seeds.
What Is Soil Blocking?
Soil blocking is a simple method which compresses a proprietary soil blend into cube-sized blocks. Standalone soil blocks allow air to penetrate roots on all sides, promoting strong root growth without constraint. Seedlings possess healthier roots and experience less transplant shock compared to pot-grown seedlings.
Good quality soil blockers (also referred to as soil block makers) range in size from ¾-inch to 4-inch cubes. You can even pair up blocks of various sizes in series—start seedlings in small blocks and transfer them to larger ones as they grow—depending on your space.
Soil Blocking Recipe
Creating a soil mix that holds form, retains moisture, and drains well is easy with the right ingredients. Standard potting soil won’t work—you’ll need a blend of peat or coco fiber, compost, soil, and sand or perlite so the blocks hold together and remain moist. Here’s a reliable recipe (yields about a gallon of dry mix), inspired by Eliot Coleman’s The New Organic Grower:
Ingredients:
6 cups eco-peat or coco fiber
4 cups perlite or coarse sand
2 cups garden soil
4 cups screened compost
A small handful of garden lime (optional)
A handful of 4‑4‑4 organic fertilizer
Instructions:
Combine all ingredients thoroughly in a large container.
Pour into a flat-bottomed tub—deeper than your soil blocker.
Slowly add water until it achieves a « wet cement » consistency. If too wet or too dry, the blocks won’t retain shape.
How to Make Soil Blocks
Insert the soil blocker into the mixture and twist when removing. Fill each mold cell, then release the blocks slowly and set them about ¼ inch apart in a tray. Drainage seedling flats are the best.
Clean the soil blocker between uses to keep blocks of even size. Place a seed in the little notch each block creates—no covering necessary. Simply make soil contact by pushing the seed gently into the block with your finger or pencil point.
Seedling Care & Transplanting
Watering from the bottom keeps soil-block structure from washing away. A light mist is sufficient initially, but for ongoing care, soak trays or spray lightly from below. Water needs will vary with climate zone and size of blocks—smaller or hotter conditions will dry faster. When you are in a week, you will have a watering routine that keeps blocks just damp.
After seedlings have a few true leaves, harden them off and transplant outside. Tomatoes, peppers, and eggplants, which are larger crops, take at least a 4-inch block to transplant. Make the holes for transplanting as large as the blocks and nest the blocks gently into the soil surface, tamping firm soil around the edges. Water well after planting and mulch with compost.
You will be amazed at how rapidly these strong, sustainable seedlings sprout. To a healthier, more robust garden this year!
