One way that we are working to minimize the use of plastic on our farm is the use of soil blocks for seed starting. This method uses metal soil blocking devices to compress a homemade potting mix to the point where it will actually hold its own shape. This entirely eliminates the waste and storage space associated with plastic potting containers.
The soil blocks have been a treat to work with so far. We have presses to make 3/4" mini blocks, 1.5" blocks, 2" blocks, and 4" blocks. Plants that are slow to germinate and have small seeds (celery, parsley, peppers, and tomatoes) start best in 3/4" blocks and are then potted on to 2" blocks. With soil blocks, this transplanting process is really simple because we can make 2" blocks that already have a 3/4" hole in the middle.
Here are a couple of photos showing the transplanting of peppers and celery. It is as easy as picking up the 3/4" block, tucking in any dangling root hairs, and sliding it into the center of a 2" block.
We love that soil blocks leave us with no waste, but it turns out there are a number of addition benefits to soil blocking. One is that, the volume of soil the roots have to explore is actually greater than a cone or pyramidal shaped pot that tapers down at the bottom. More space leads to more roots and healthier plants. Another benefit to the soil blocks is air pruning. Because the outer edge of the soil blocks are exposed to the air, the plant roots self prune once they reach the edge of the block. The roots continue to develop within the block but do not wander beyond the edge. Once the blocks are transplanted into the garden the roots are ready to expand into the great unknown with minimal disruption. In plastic pots, roots can quickly become root bound by wrapping themselves around the inner walls of the pot searching for space. The roots then need to be opened up when transplanting and this causes unecessary stress on the plant.
Overall, our investment in the soil block forms seems like a wise decision so far. The blocking process is simple, efficient, and modular, and the forms are clearly built to last. They will help us grow thousands of healthy seedlings in their lifetime with zero plastic waste.