By Rebecca Thieret
From seed trays to mulches to packaging, the use of plastics in agriculture is commonplace. Plastic waste is a major environmental problem in the United States. 63 pounds of plastic per person end up in landfills every year in the US, accounting for 16% of municipal waste (Discover Magazine, 2009). Lots of plastics used in agriculture cannot be recycled, contributing to this waste problem. As organic farmers, we strive to use practices “that foster cycling of resources, promote ecological balance, and conserve biodiversity” (USDA, 2012). Using soil blocks instead of seed trays can help prevent tons of plastic from ending up in the landfill every year.
What is a soil block? A soil block is compressed soil in the shape of a block (surprise!) used to grow seedlings, in place of peat pots or seed flats. Of course, there are advantages and disadvantages that go along with using soil blocks. In plastic flats, seedlings can easily end up root bound, leading to stunted growth. In soil blocks, roots actually air prune themselves, promoting healthier root systems (Walker, 2005).
Watering and erosion can be an issue with soil blocks, but with the right set-up and methods, this can be easily overcome. Since 5 sides of the plant are exposed to air, soil blocks can dry out quickly. However, with too much watering, the blocks will fall apart. Frequent misting is the best method, which is why our seedlings are starting out in the mist house. At home, watering from below might be the best method.
The use of soil blocks for growing transplants can also help avoid transplant shock. Pulling delicate seedlings out of pots and putting them somewhere else can be very traumatic for the seedling and lead to slowed growth and damaged roots (Urban Garden Magazine, 2010). When soil blocks are used, the plant can simply be placed (soil block still intact) into a pot or larger soil block.
From my experiences working with soil blocks, I have found them to be effective in producing healthy seedlings as long as they are taken care of right. In order to live up the The National Organic Program’s standard that we “foster cycling of resources”, organic farmers should continue finding new, creative ways to reduce all types of waste coming from agriculture, including plastics.
Discover Magazine. October, 2009. Plastics, From Manufacturing to Recycling to Long Death in a Landfill.
United States Department of Agriculture. February, 2012. National Organic Program
Walker, J. 2005. Guidebook for Native Plant Propagation: Development andconstruction of an air-pruning propagation bench, and its proper use. Washington University.
Urban Garden Magazine. April 7, 2010. GrowerTalk: Transplant Shock.