Goals and expectations for our winter heat sink greenhouse

It recently occurred to me that we have not taken the time to outline our goals and expectations for our winter heat sink greenhouse. If you watch some of our previous videos you will catch bits and pieces, but we have not yet laid everything out together in the same place. In this blog entry and video I hope to collect our thoughts, goals and expectations in one place.

If this is the first time seeing our stuff, you may want to finish this paragraph as I give a brief summary of this project. If you're familiar with what we are doing, jump to the next paragraph. In our back yard we have built a 20 by 45 greenhouse that has a 95 ton rock heat sink under it with the purpose of providing enough heat through the winter to grow food all year long. The heat sink is about 4 feet thick and is insulated on 4 sides with 4 inches of foam. The foam keeps the cold from the soil outside the greenhouse from getting inside. It allows the rock to hold heat that releases into the greenhouse at night. During the day the heat from the peak of the greenhouse is pushed through the rock with a fan. There is a little more to it, but that gives you the basics. To see more we have a bunch of videos in a playlist on YouTube.

So, as to the goals and expectations for our little winter heat sink greenhouse. When all of this began I was interested in being able to grow my favorite tomatoes all year long. With our home being in northern Missouri where our winter temperatures get well below freezing our only option would have been a propane heater of some sort, or a wood burning furnace.

Both options were a deal breaker for the hope of growing those tomatoes through the winter. Propane would be easy, but very cost prohibitive for growing tomatoes for personal use. There is a lot of firewood on our property, and we have all the tools necessary to harvest and process it into usable firewood. The problem we had with the wood burning furnace is the need to constantly be present to keep it stoked and producing heat. That would make it difficult to be away from the home for an extended period of time. A wood burning furnace would also require trips outside in the cold and dark to keep those greenhouse temperatures in the safe zone. Neither was a good option for us, so no winter tomatoes on our homestead.

With the hope of fresh January tomatoes no longer an option, we started looking at growing hardy crops that can tolerate some freezing temperatures for short periods of time. It would be far easier to keep the greenhouse temps at a level where the hardy crops will survive through the cold nights.

Our goal for the greenhouse was twofold. First, we wanted to significantly extend our growing season by being able to grow crops in a greenhouse. The greenhouse allows us to start crops before our average last day of frost and continue to grow well past our average first frost in the fall. That goal was easily achieved just by constructing the double walled greenhouse. Secondly, we wanted to be able to grow a hardy crop all winter long to ensure we have fresh vegetables all winter long.

Our coldest months are January and February. We expect during those months we will need to cover each grow box with a mini hoop house to keep temperatures suitable for our hardy crops. It will be easy to make the arches from PVC to cover our crops. As we transition into spring and the temperatures come up, we will simply remove the hoop houses and rely on the greenhouse to provide the needed protection.

We came into this expecting to only grow food for us, with the possibility of selling a little extra to help offset the cost of the greenhouse. ( If we had the goal of doing this for profit we would have gone with a larger structure. ) Selling produce in the winter months makes sense to me there will be few, if any, people in our area selling fresh locally grown produce. This would allow us to demand a higher price than during the summer when there were several other people growing and selling produce.