Saturday, January 24, 2009


My newest garden project is a greenhouse. I have spent this winter researching and designing a small (6x10') greenhouse for our backyard. It is the greenhouse project that is largely responsible for this blog- to share ideas and get help from gardeners.

Our greenhouse will be used year round; we plan to use it to extend the growing season by a couple of months for our usual vegetables and in the winter we plan to grow hardy vegetables- nothing too fancy or exotic: lettuce, spinach, Brussels sprouts, beets, and similar. I love hot Thai peppers and this is another reason for the greenhouse, to fulfill my peppery dreams.

We do not plan on heating the greenhouse much, but we will to keep it above 35- 40 in the winter. One interesting thing we are planning is to heat the greenhouse with compost. I am not sure if it is going to work, but I am going to give it a try. The worst case scenario is we will have storage in the greenhouse and compost that actually decomposes in the winter.

For our "compost furnace" I am planning to dig a 3x3x2 ' (deep) pit in the floor of the greenhouse that will act as the compost pit. The walls will be lined with plywood and 2" rigid foam insulation so heat does not get lost to the ground. Over the top will be an expanded steel grate to walk on and allow easy watering and ventilation. I am not sure if there will be enough mass to really heat the greenhouse, but at least the compost will break down faster than it does outside in our backyard.

The rest of the greenhouse is going to be made from recycled materials as much as possible, and I have already begun accumulating various pieces. Even though I won't start building the greenhouse for a few months, most of the pieces I have had to collect ahead of time so I could design the greenhouse. I have all the windows, doors, exhaust fan, lighting, and more.

The greenhouse will be small- mainly due to our small lot, but hopefully it will be well designed and efficient. The north wall will be conventionally framed with 2x4's and insulted with r-13 fiberglass bats, the north end of the gable roof with be constructed similarly. The south wall the south slope of the roof, will be glazed and about 50% of the east and west walls will be glazed.

I am still working ion the details of the foundation, but in any case it will be insulated with 2" rigid foam, and there will be a concrete floor, except on the south end where it will be opened to the ground for a raised bed.

Soon I will post some drawings of my greenhouse plans and pictures of the piles of materials that are filling up my woodworking shop.


  1. That sounds really innovative.

    Another insulating idea would be using one of those adjustable heavy-duty plastic compost bins (that some cities give away). You could cut it in half so ea piece was about 2' tall. If you staked the plastic barrier 4" from the edges of the hole you could fill the 4" gap with some straw of other brown material. This would provide insulation as well as become compost by mid to late summer once you are turning the entire pile. At the start of the next winter you could repeat the process with new straw or whatever. Just a thought.

    I'm looking to do a similar thing and have been throwing around ideas myself. I've also heard of having a connected compost area (separately insulated) next to the GH and using piping to transfer the warm air into the GH. I'm not sure which method would be more difficult but at least the "connected" method would solve the issue of having to bend over so much as required with an in-ground compost. I guess both methods have their pros and cons...

    WA State

  2. Great ideas- thanks for sharing. I'm interested to hear what you decide to do. The idea of an external compost furnace is a good one, and I have read a bit about it. My concerns would be the efficiency of transferring the heat, the added space and making another insulated space for the compost. I'll keep you posted on how my ideas progress. Thanks again.