What do you think of when you hear the word hotbed in the context of gardening, you probably are thinking of a planting bed that are heated from below with a heater. Well if that is what you are thinking your are correct, some hotbeds are heated with a coil heater or a heating mat of one variety or another using electricity to heat the coil or mat. Here is a much greener method which will work just as well as most methods using electricity. By using recycled materials that you have around, you can save a lot of money. I happen to have a lot of small Eastern Red Cedar trees that need to be thinned out so that is what I used.
Step 1: Rough Fitting the Poles
The first thing I do is go and get the poles, decide which ones will work for which side etc., lay them out in a rough plan. Then comes the cutting of the notches I like the notched log method for putting them together. You can use recycled pallet lumber, most pallets are made from oak so they will last a few years, just make sure they are the heat-treated variety not the chemical treated ones. Any recycled lumber that you may have laying around would work well also. With that said let’s get to putting this hotbed using poles together.
Step 2: Finishing the Frame
Finishing up the frame with the saw so that the poles fit snuggle together to hold in the heat at night.
Step 3: Digging Out the Soil
After finishing the frame, you will need to dig out the ground down 18 inches below the bottom surface of the frame. This will allow for the green manure in the bed to heat up and keep the bed warm even on cold nights.
Step 4: Add Green Manure
The next step is to add some green manure, what is green manure you ask it is manure that has not been composted. Usually straight from a stall or paddock works well. After adding the manure I spread it evenly to ensure even heating up the the bed to hold the heat at night.
Step 5: Adding Black Plastic
After the manure is placed and spread evenly in the bed, I like to put a layer of black plastic to help generate even more heat during the day which will help the plants stay warmer at night. Holes should be perforated in the plastic to allow water drainage into the manure base, otherwise your plants run the risk of drowning the roots, and causing dampening off. Good air circulation is a must for all plants.
After you have placed the plastic to your liking, attach it to the wall to keep it in place with some small staples. Attaching it will help keep the extremely cold air out during a sudden cold snap since my logs are not perfectly sealed.
Step 6: Adding the Window Cover
Once the plastic is attached then comes the next recycled material, a window, this particular one is 3 feet by 6 feet so that is the size of the bed that was constructed. You can attach the window with hinges if you like so that it be easily propped open for air circulation during the day, I am not attaching the window on this particular bed because my window opens so that will work for air circulation and I plan on this being a herb bed once the seedlings are done with the hot manure. This window still works so on bright sunny days when the bed will tend to get too warm it can be easily opened for good air circulation.
Step 7: Adding the Plants in Pots.
Once the window is in place you are ready to put the pots of seeds in here and watch them germinate. Again use any pots that you can recycle, yogurt cups, milk cartons, old planter pots, etc. to help save on the cost of your Great Garden. If you are reusing old plant pots to give them a washing with a light mixture of soapy bleach water to ensure no pathogens are passed on from the nursery pots. This particular hotbed is pretty shallow only about 10 inches from the top of the window to the top of the plastic but it should allow for a good start on seeds until the weather warms up. Any plant over 10 inches can and should be moved to the garden, if it is still not warm enough for tomatoes and peppers I move them to a larger cold frame for protection of the elements. A green manure hotbed can give you a great jump-start on the garden, getting your cold weather plants ready sooner and even starting tomato and pepper plants. This method has worked well for me starting even the harder to germinate hotter peppers (Habaneros, Cayenne, Pablanos). Peppers like a constant 70 degrees to germinate properly and remember they can still take 21 days to germinate. In a 4×8 bed 200 plus plants can be started. I really like this method for starting seedlings because not only can you start a lot of seeds, to save money not having to buy plants, the plants also are much hardier in my opinion. The natural method of heating up during the day and maintaining a good warm temperature at night but not getting too chilled makes for a healthy root system and plants that do not get leggy while growing or do they get as shocked as bad when you move them outside.
Step 8: Proof Is in the Thermometer
As you can see there is clearly a 20 degree temperature difference between the ground and what is being created in the germination bed on a cool cloudy day. 73 is perfect germination temperature. On bright sunshine days with the outside temperatures above 65 you will want to open the glass some to let out the hot air so you don’t cook your plants. As you can see there is clearly a 20 degree temperature difference between the ground and what is being created in the germination bed on a cool cloudy day.