Hotbeds for Winter Growing

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October peas growing in a hotbedIf you’ve been following this blog recently, you know full well that I’m focused on growing veggies this winter. Today I want to share some details with you about one of the most important parts of my winter veggies strategy – hotbeds.

To recap what I shared in a previous post about winter gardening, hotbeds include:

“a pile of decaying organic matter warmer than its surroundings due to the heat given off by the metabolism of the microorganisms in the decomposing pile.

A hotbed covered with a small glass cover (also called a hotbox) is used as a small version of a hothouse (heated greenhouse). The bed is often made of manure from animals such as horses that pass much undigested plant cellulose in their droppings. Thus hotboxes are to cold frames what hothouses are to greenhouses.” (Wikipedia)

A hotbed can be used to extend the growing season into late fall or winter. They can also be used to get a jump start on the season in early spring. Although there are many options for creating electrically heated hotbeds, I wanted to find a more natural and less fossil-fuel-dependant way to make it work. (Maybe solar-powered electric hotbeds will be in Arcadia Farms’ future someday? Who knows…)

How To Build a Hotbed

Want a hotbed? Here’s how I converted our existing raised garden beds into hotbeds.

Step 1: Empty the bed. I simply used a shovel to remove all the garden soil. (I piled it into a nearby bed.) Then I used a utility knife to cut the landscaping fabric we laid underneath all of our beds to keep weeds out. Our beds are four feet wide by twelve feet long. I left a six inch “ledge” on all sides to support the frame of the garden bed.

Half empty raised bed garden

In this picture you can see the remnants of some of landscaping fabric used beneath our raised bed. The fabric keeps weeds and grass from growing through the soil in the bed. I removed it by using a utility knife to cut six inches in from all sides.

Step 2: Dig a pit 2.5 feet deep. Pretty simple. Get the shovel out and get to work. In our area we have decent but somewhat sandy soil. I’m keeping the dirt I remove to compost with organic matter like leaves, grass clippings, bunny poo and table scraps so that it will be useable soil for future raised beds.

Pit in bottom of raised bed garden

Step 3: Gather manure. “Hot” manure like horse, cow or chicken is best. The manure should be mixed with about 1/3 straw or similar bedding like sawdust, shavings, etc. The straw helps to keep the heating uniform and longer lived.

Our first hotbed has two kinds of manure in it: Goat manure and horse manure. I’m sorry to say that I have temporarily misplaced my soil thermometer (blurgh…) so I can’t tell you specifically how well the horse manure has performed since I added it, but the goat manure reached temperatures as high as 100*.

Step 4: Heat the manure. Just pile the manure (no more than four or five feet high) and dampen it with water. (Damp is the key, you don’t want it to be soggy.) After three or four days the pile should be turned to ensure even heating. After 10 days, your manure should be well heated.

Step 5: Fill the pit with manure. Add six inches of manure and tamp it down firmly. This, again, is done for even heating. Tamping the manure down will also avoid lots of settling as it decomposes. Repeat this process until you’ve added three layers (18 inches) of manure. I also added some grass clippings and leaves from last fall.

Leaves and grass clippings in hotbed pit

First I added a layer of leaves and grass clippings.

Goat manure and straw in hotbed

In this picture you can see the goat manure and straw that I added to the hotbed.

Goat manure and straw

Goat manure and straw. Can you believe this stuff starting baking to 100*? This picture was taken before I tamped it down.

Step 6: Add planting soil. Now you’ll want to put your planting medium (I’m using compost mixed with peat moss and vermiculite) on top of the manure. Just add six inches.

At this point, your soil is probably going to be quite warm, upwards of 100* or more. Let it sit for a few days until the temperature drops down to the proper germination temp for the plants you’ll be using. Many plants germinate somewhere between 65* and 75*, so I recommend waiting until the soil temperature is around 70*. Keep in mind, soil temp and air temp are different. You’ll need one of these soil thermometers to gauge your temps.

Originally I put all 12 inches of garden soil back on top of the goat manure. I measured the temp right away – 58*. Twenty-four hours later I measured again – 58*. I was pretty bummed! I dug up all the soil and started to remove the goat manure… until steam started rising from the bed! This is when I discovered that the temp was 100*. Instead of putting all the soil back, I just added six inches. Viola! Twenty-four hours later the temp had begun to rise and was at 68* -almost exactly where I wanted it.

Raised bed converted to a hotbed

Here you can see the soil is back… all 12 inches. I later removed the top six inches because 12 inches was just too much to heat. The plastic to the left o the picture goes over the PVC hoops (you can see one at the end of the bed) and is secured with clips and logs.

Step 7: Cover the bed. Covering the bed provides insulation but should also allow maximum light in for solar heating and photosynthesis. Most hotbed plans call for used windows set on a wooden frame with a two foot tall northern side and a one foot tall southern side. But in an attempt to be resourceful, I’m using polythene plastic row covers on PVC pipe hoops.

Now What?

As I mentioned above, I unfortunately misplaced my soil thermometer, so I can’t give you a report on the temperature progress in the first hotbed. However, I can tell you that the peas I direct seeded into that bed are coming along quite well! The air temperature in the bed has varied just as much as our October weather. I think the lowest temp this month was in the 40’s and the highest was well over 100*. On sunny days I’ve been trying to remember to open both ends of the row cover for ventilation. (The bed runs east to west and gets a good breeze.)  Because we’ve had plenty of rain, this is the only part of the garden I’m having to water. (Remember, it’s covered with a row cover right now.) I’m watering about once a week if needed because the soil is holding water well.

Hot bed with row cover and peas

Here’s the hotbed after a couple of weeks. The seedlings you see inside are various kinds of peas. The ends of the cover are open for ventilation since it has been very sunny the last few days and air temperatures were reaching 100*+ inside the bed.

October peas growign in a hotbed

Peas :)

Because the manure will only keep its heat so long, I’m going to wait to fill my other five beds. The plan is to take advantage of the sunny weather we’ve had lately to get all the beds emptied and pits dug. I’ve been so busy with other tasks that I still have a lot of digging to do and, frankly, am getting a little anxious that I might run out of good-weather days to get it done.

I’m grateful to my friend Jennifer at Hannah Hill Nigerian Dwarf Goat Farm for providing me with goat manure and will also be getting more horse manure from my friend Laura whose father has horses on his farm. I think I may be the only girl on the block who plans to have piles of manure out back waiting for the cold weather to arrive! I’ll be keeping a close eye on the weather so that I can wait as long as possible to put the manure in the ground without waiting so long that my teeth are chattering while I do it! I also need to consider the transplanting needs of my seedlings, although they should have at least two more weeks in the greenhouse before they need to be planted out and can go longer than that if needed.

Now. Time to go pick up a shovel and start moving some dirt… this decent weather won’t last forever!

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