We get lots of questions about our hot bed, which we use to start our farm's early seedlings in the spring, like around mid-March. So I thought it would be prudent to put together another, better how to, with pictures! Here goes.
STEP ONE: Procure manure. Important here: use ONLY fresh horse manure mixed with sawdust/pine shavings bedding, or straw or hay. Using other manures sometimes can kill your seedlings if there is too much off gassing ammonia. It's happened to us, don't let it happen to you!
STEP TWO: In your high tunnel or greenhouse, lay out hay or straw bales ON THEIR SIDE in a long rectangle that is one hay bale wide (about 3 feet) by however long you want it to be. (A 35 foot bed starts about 75 1020 flats, we've found. More if you stack seed trays to germinate them.) You want the hay bales on their side to give you as much compost as possible -- if your bed is to small or narrow, the pile won't have the critical mass it needs to start heating up and composting.
STEP THREE: Fill your newly created straw/hay box with manure! Make sure it is heaping high, as in the first few days the manure will settle quite a bit as it composts down.
STEP FOUR: Let the manure settle for a few days, and it will begin to get warm and steam. At this point, cover the manure with an inch or two of finished compost, soil, or woodchips. I think this helps to temper some of the heat of the pile and capture some of the ammonia that may escape. I don't think this step is essential, though. At this point, pound in rebar on both sides of your hay bed and put in PVC hoops that will serve to keep your plastic and row cover off your seedlings.
STEP FIVE: Rake the composting manure flat after a few days, and cover the bed with pallets (or something else that keeps seedlings directly off manure) This keeps air flowing beneath the seedlings and keeps them from eventually rooting into the compost. Put one or two layers of row cover (we use Agribon 30 for its warming properties) over the hoops and measure the temperature in there before starting flats inside.
Finally, cover your bed with a layer of contractor plastic as extra protection against cold nights. The row cover and plastic are ESSENTIAL for making sure seedlings don't freeze on extremely cold nights. And they work! It was three degrees outside the other night and inside the seedlings were at a balmy 65 degrees.
Congratulations! You've used a waste product to produce heat that will help you produce food for your community. And, you've avoided using propane.
Some things to consider: in a few weeks, the heat will die down and you may want to extend your hot bed further. Turning the bed is complicated, so I would just recommend making another bed.
In the late spring when you want to plant your high tunnel, just tear down your hot bed, and the manure should be composted enough to work into your soil! Make sure that you do supplement with nitrogen because the compost won't be totally broken down.
Rats are a big problem, because they like a) living in giant, warm saw-dust filled beds in the winter, and b) they like to eat seedlings of very expensive plants, like broccoli and peppers. I give you permission to trap them with any means necessary.
If you have questions, e-mail us at plowbreakfarm.com.
Come check us out at the Tompkins County CCE's annual CSA fair!
The event will be held this Saturday, 12-3 at Boynton Middle School in Ithaca.
We'll be there with our friends Liz and Steve of Wellspring Forest Farm, who have a shiitake mushroom CSA share add-on for our share this year.
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