So my new, latest and favourite technology turns out to be a pile of crap. Literally. It’s called a Bio Bed. Or a Hot Bin. And I’d like to thank Heather at Uminami farm in East Sooke for introducing us. The Bio Bed is an old Japanese technology and a new permaculture re-skilling favourite, embracing natural systems, involving no moving parts, and totally off-grid.
It is a common practice for growers to warm their seedlings to get them going in the early spring. This involves sitting the seedlings on a warmed bed. Typically the warmth comes from electrical heating coils embedded in sand under the seedling trays. These heating coils are expensive and prone to failure, and its not a great idea to get them wet. Not to mention they use grid electricity.
We had conceived a couple of designs to create and off-grid version of the seedling warming system. The first used PV panels to drive elements from old hot water tanks. The second was a solar-thermal system with a small solar pump. Then Heather showed us the Bio Bed.
The Bio Bed is simply, has no moving parts, is basically free save our labour. And when done, the bi-product is beautiful compost. It doesn’t get more permaculture.
The Bio Bed is basically a hot compost pile inside your greenhouse. The decomposition process generates heat if you get the Carbon:Nitrogen ratio correct and close to 30:1. We used horse manure from a local stable where the kids take lessons. (While they rode – we shoveled.) Horse manure has a C:N ratio of about 18:1, so more carbon was required. Fortunately, the pile of manure we draw from had some Fir chips mixed in. At a ratio of 400:1, Fir chips are mostly carbon. Our guess was that the mixture was about right.
Turns out we were right, the mixture was about right. The Bio Bed is averaging about 35C in the pile and about 20C on the surface. It is warm to the touch but not hot. Let’s see how the seedlings do!