Tuesday, December 14, 2010


An item of great interest at the Market this season has been hoop houses. It seems many vendors either have one or are considering one.

What is a hoop house?

The best definition is that it is an unheated greenhouse. Most hoop houses are built with steel or plastic arches, or 'hoops', and that is the basis for the name. But whatever materials are used the primary distinction between a greenhouse and a hoop house is that the hoop house is not heated.

What can you do with a hoop house?

You can extend the season. If you cover your plants to protect them from frost in the fall, a hoop house will do this much better. In the spring a hoop house will act like a cold frame and allow plants to be started earlier. A reasonable estimate is to expect to extend the season from about two weeks to a month in both fall and spring.

You may be able to 'over winter' plants that are not normally be hardy in this area. The hoop house captures passive solar heating and provides some insulation. It also provides protection from wind and rapid temperature changes. The climate zone in the hoop house is probably increased by 1/2 to 1 USDA zone. Ann Arbor used to considered zone 5, with climate warming many charts now consider it to be zone 6. A well designed hoop house should be able to keep most zone 6 and some zone 7 plants alive over winter. This will depend on the plants, the design of the hoop house and the severity of the winter.

You can harvest cold hardy plants later in the season. My wife occasionally sends me out to our herb garden to cut fresh herbs in the winter. Plants like oregano, thyme and sage are winter hardy. But it is troublesome to find them under a blanket of snow. A hoop house makes this much easier.

Can you grow plants in the winter?

Not really, most plants require about 65 degrees F for photosynthesis. This will not occur in an unheated hoop house in a Michigan winter. To actually 'grow' plants, that is to have the plants increase their vegative mass during the winter the building must be heated.

What vendors at the Market have hoophouses?

The ones that I know have hoophouses are Shannon Brines (Brines Farm), Dwight Carpenter (Carpenter Organic Produce) and John Hochstetler (Farmer John of Our Family Farm) Much of the information of this post is a result of conversations with Shannon Brines and Dwight Carpenter and visits to their hoop houses.

Brines Farm

Shannon Brines (Brines Farm) was one of the first vendors at the Farmers Market to construct a hoop house. They are now growing plants in three separate hoophouses. Shannon plants cold tolerant greens in the fall and uses the advantage of the hoophouse to continue to grow them in an extended season. The greens survive all winter with the hoophouse protection and Shannon harvests them and sells them all winter at the Market.

Brines Farm uses all of the potential hoophouse advantages to produce and sell excellent greens all winter. Much of their produce goes to the members of their CSA program customers. The produce has such a good reputation that they often cannot meet the demand from other customers.

Here is link to the Brines Farm website: http://www.brines.org/

Here is a photo of one of their hoophouses.

Carpenter Organic Produce

Carpenter Organic Produce also has three hoophouse. In addition, Dwight also has one large heated greenhouse constructed in the manner. Some photos from Carpenter's green house are on the May 8, 2010 post of this blog. Some photos of his excellent produce are in the previous post on this blog.

John Hochstetler (Farmer John of Our Family Farm)

I have not visited Our Family Farm and do not have any information about their hoophouse. The produce they have been bringing to Market have been a hardy salad mix of spinach and members of the cabbage family. These greens have been very good, particulary when used in an oriental stir fry dish.

Here is a link to their website  with a photo of their hoophouse : http://www.ourfamilyfarmllc.com/ The hoophouse is a larger version of plastic pipe construction.

I discussed hoophouses with John on Dec 18, and he mentioned that at least one of his hoophouses was heated. To me, this would make it a green house, but there was an interesting aspect of his method of heating. His lettuce is grown hydroponically and he heats the hydroponic solution. For the small producer that wants to grow plants that do well in a hydroponic system this is an ideal approach. If you are concerned about organic production, it is possible to grow organically, even certified organic, with the correct hydroponic nutrients.

In a few days I will add a post discussing how a hoophouse works and how they might be improved.

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