With increased interest in sustainable farming practices, there are many on-farm practices that can be considered. One practice is soil blocking, maybe most well-known for being discussed in Elliot Coleman’s “The New Organic Grower.” Soil blocking is a method of sizing up transplants in molded blocks of soil as opposed to plastic pots. The practice is said to reduce root circling, leading to increased yield, earlier harvest and more resilient plants. The practice also cuts back on the amount of on-farm plastic.
by Marissa Schuh and Will Jaquinde, Michigan State University Extension
Our goal in this trial was to see if starting plants in soil blocks increased yield or decreased the time to harvest. To test this, six commercially available indeterminate tomato varieties were potted into either in a traditional pot or in a soil block at Tollgate Farm and Extension Center in Novi, Michigan. Pots were 2.75 inches long by 2.75 inches wide by 2 inches high (11.88 inches³). Soil blocks were created using the stand up six-cell blocker from Johnny’s Seeds, which created blocks 2.375 inches long by 3 inches wide by 2 inches high in dimension (14.26 inches³). The blocks have a larger volume but because wet soil is pressed into the blocks, the weight of dry soil in each treatment was comparable (41g in block, 35g pot).
These transplants were then planted in a hoophouse or in the field. Yield was tracked through the growing season. In our trial, the methodology used to start the transplant had little effect, with variety being the most important factor in yield. For full details about the materials, methods and statistics, see the full report in the 2018 Midwest Vegetable Variety Trial Report Bulletin.
While differences were present among varieties, there were no differences between the hoophouse or field setting for per-plant yield of tomatoes started in traditional pots and tomatoes started in soil blocks (α=0.05).
The amount of time it took to prepare pots and blocks was similar, though preparing soil blocks has more nuance and is more physically demanding. It can take trial and error to find a soil mixture that will hold its shape when blocked, and adding the right amount of water to get the soil mixture malleable but not overly wet can add time to the blocking process.
There was a difference in plant height at the time of transplanting. Tomatoes grown in soil blocks were taller than those grown in pots (39.7 inches versus 27.8 inches, LSD.05=1.97). No significant root circling was noted in either treatment.