Discovering Soil-Block Making, by Eliot Coleman

Soil-blocking is an ingenious seed-starting method that allows the grower to produce vigorous seedlings with roots that quickly reestablish growth upon transplanting. Soil-blocking further eliminates the expense, waste, and storage issues associated with plastic pots. Read Eliot Coleman's account of how he came to develop and perfect this system for the small commercial grower.

Artichoke seedlings in wooden flats

When we started as commercial vegetable growers in 1969 we used to grow our seedlings in wooden flats filled with potting soil. We kept a series of marker boards with dowels set at the ideal spacing for the different crops, which we would place on top of the flat to make indentations in the potting soil where each plant would go. Some crops were direct-seeded into the flats, but others we would germinate in seedling flats and then transplant into the growing flat at the proper spacing.

Eliot, watering the emergent seedlings

Once the seedlings were large enough to set out in the field, we would use a sharp knife to cut the flat into cubes, each containing a plant, as if we were cutting a tray of brownies, before transplanting them. The advantage of this system over bare-root transplanting was that each seedling came with its own, mostly undisturbed root ball, enabling the transplants to become established quickly in their new home.

When the early "Speedlings" and plug tray systems first came out, we tried them but didn't like the results as well, because the plants didn't seem as vigorous or grow as rapidly. A bit of geometry taught us why. An upside-down pyramid has only one-third the volume of a cube of the same top diameter. So we went back to our wooden flat system but continued to hope to find something even better.

Eliot's air-pruned onion seedlings

I first saw that something better on a visit to European farms in 1976. One of the small farms I visited was growing seedlings in soil blocks. Not only did the soil blocks contain the two-thirds greater soil volume mentioned earlier, but the separation into cubes had taken place even before seeding, so there was the absolute minimum of root disturbance.

European research further brought to light that the roots of container-grown seedlings encircle the container's inner surface, whereas roots growing in soil blocks "air-prune" themselves at the block's surfaces because of the separation between the blocks. On transplanting, the soil-block plant roots extend immediately into their new surroundings, and establish themselves three days sooner than the container-grown plants that have to learn to stop circling.

I was hooked — but I wanted more. The smallest size block that the early hand-blocking tools would make was 1½ inches square. I wanted smaller germination blocks for crops I started with bottom heat, such as tomatoes, peppers, eggplants, and celery, so I could fit more seedlings on each heating mat.

I convinced a British manufacturer to make a mini model for germination purposes (¾-inch x ¾-inch blocks) and to make similarly sized pins (or dibbles) to poke holes in the top of 2-inch blocks, so the germinated seedlings could quickly be potted on — the square block in the square hole. This was now a complete seedling-starting system.

Transplanting soil-blocked seedlings

There will always be a few blocks left empty in a flat where a few of the seeds did not germinate. Even so, these were not a total loss. When my children were younger they helped me with transplanting in the field. The empty blocks were the summer replacement for winter's snowballs — now called dirtballs — with which they would happily pelt each other.

Further Resources

• Soil Blocking: A Better Way to Start Seedlings • Article
• Guidelines for Starting Seeds Indoors: Tips & Troubleshooting Advice for Starting Healthy Seedlings • Article
• How to Make Soil Blocks + The Advantages of Soil Blocking With Niki Jabbour• Video
• How to Use Soil-Block Makers • Video
• Johnny's Hand-held 12 Soil Blocker • Instructions & Use • Tech Sheet (PDF)
• Seed-Starting Date • Interactive Calculator
• Seed Starting at Johnny's Selected Seeds: 3 Systems for Indoor Seed Starting • Article
• Soil-Block Makers • Instructions • Tech Sheet (PDF)
• Shop Soil-Block Making Tools • Product Listing
• Shop Seed-Starting Supplies • Product Listing
• View Crops to Start-Early-for-Transplants • Product Listing
• View Eliot's Books • Product Listing