A question came up at The Greenhouse Project, a nonprofit raising food for the food insecure in Carson City.
“Would plantable biodegradable planting pots work to reduce transplant shock, labor, and petroleum-based container waste?” These type of planting containers have been around for more than 40 years, starting with peat pots.
Putting a seedling in its starter pot directly into the soil or a larger container without pulling it out first, seems a good way to reduce shock. It also eliminates a step in the potting up process. Ideally, the plantable pot would decompose in time for the young seedling’s roots to grow out into the main soil of the bed or larger container. Since the rate of the pot’s decomposition is determined by the amount of organic maatter, biological activity, humidity, and moisture in the soil, as well as the soil’s pH, results are quite variable. Seedlings at TGP are planted into highly amended soils in raised beds under drip irrigation or grown in pots of soilless mix on benches in the greenhouse.
Cory King, TGP’s farmer and manager, has found in the past that planting seedlings in their biodegradable pots didn’t work well. The pots actually hindered root development, because the roots couldn’t break through the sides of the pot into the surrounding soil. Decomposition was far too slow.
Outside in the planter beds, this may have been influenced by Nevada’s low humidity, which quickly reduces soil moisture. In addition, cold soil temperatures slow the decomposition process. In the greenhouse, although the humidity and temperature stay fairly constant, microorganism activity is quite limited in containers and, without microbes, decomposition doesn’t occur. Biodegradable pots are also known to wick moisture away from roots and surrounding soil, drying plants out.
As I researched this, I found that a better application for using plantable biodegradable pots might be in landscape situations, rather than for food production. In a landscape we can plant a perennial, shrub, or tree in the ground in its pot and if the conditions are right, the pot breaks down over time. This eliminates petroleum-based plastic waste. However, with Nevada’s short growing season, low humidity and low soil organic matter, the biodegradable pot might take years to decompose, and this could affect plant development.
A way to reduce plastic use at TGP might be to use biodegradable pots in place of traditional plastic pots for seeding and seedlings. When a plant was transplanted, it would be taken out of the biodegradable pot, same as out of a plastic pot. When the pots wear out, which they do more readily than plastic, they can be composted.
JoAnne Skelly is Associate Professor & Extension Educator Emerita at the University of Nevada Cooperative Extension.
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