3 feet deep and lined with bricks to hold and distribute the heat.

A couple of weeks ago Eric and I were talking on Gardenfork Radio about his new DIY Cold Frames video, and I mentioned winter gardening in hotbeds.  I’d seen some hotbeds in the garden in Colonial Williamsburg, where they still garden the way colonial people did.

Hotbed are like Eric’s cold frames with glass on top and all, but deeper.  Last weekend we went up to the Williamsburg Farmers Market for their big pre-Thanksgiving holiday market and I took some pictures of their hotbeds to show Gardenfork readers.

What makes hotbeds particularly attractive to the DIY organic gardener is that you get a twofer.  First, you use the otherwise wasted heat of composting to get an early start on Spring.  Second, you have fresh, finished compost to spread on your garden.

A hotbed needs to have a mass of at least 1 cubic yard to be effective.  That’s because what you’re building is  a compost pile and compost needs mass to really cook.  So these beds are deep:

— It helps to line a deep hotbed with plastic sheeting or weed block fabric to aid in cleaning it out in the Spring.
— Layer in browns (cabon): dry leaves, leaf mold, spoiled hay and bedding from a stall.
— Layer in greens (nitrogen): kitchen waste, fresh manure.

Hotbeds are an excellent use for chicken manure as well as horse manure, which can be “seedy” in the compost otherwise.  Cattle manure is good too.

If done right, enough heat will be generated to kill all seeds, worm eggs, and pathogens.  In fact, hotbeds have been known to combust and smolder if too big.  Obviously, you don’t put compost worms into a hotbed to help with the composting unless you want them to cook.

add 12 inches of rich growing soil onto the top of the fresh manure.

— Add about 12 inches of good soil for growing.

— Carefully manage your glass frames so that your plants don’t overheat.

Hotbeds are an ancient method of sprouting seeds and growing plants during the winter, Aristotle mentions the Egyptians using compost piles to sprout seedlings.  Europeans imported hotbeds from Arab countries after the Crusades.

In fact, the colder and more sunless your winters, the more hotbeds will help you get an early start on the spring garden and bridge what was called in early colonial America the Starving Time, January to March, after harvest stores from the previous fall had run out but before plants would grow in the frozen fields.

Hotbeds don’t have to be buried, either.  The Romans had hotbeds on carts so that they could be moved under cover when it rained.  In medieval Europe, hotbeds were frequently just dung heaps that people planted vegetables into over the winter.

Manage your hotbeds like a coldframe. Overheating is as dangerous to your plants as freezing.

But regardless of how you build your hotbed, proper timing is important.  Few plants or seeds can tolerate the intense heat of an early hotbed.  So start your hotbed a month or two before you plant.  So plan to plant or seed on the backside of this period, when the hotbed is warm but not hot.

And remember, you have to manage the moisture content of your hotbed, just like a compost pile; neither too wet nor too dry.

And when you hear on the news that a place is a “hotbed of political activity” you’ll know what they’re full of.  ;->

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  1. Denis says

    I always liked the idea of hotbeds and you’ve reenforced my belief. I’ll start my own project, just have to persuade my wife too.

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