winter greenhouse growing

Asked August 3, 2014, 2:40 PM EDT

Thank you for the information you sent on gardening. However, I am interested in winter greenhouse growing for a 6x8 hobby greenhouse. Do I need to heat the greenhouse if I grow winter vegetables? If I want to grow tomatoes how much do I need to heat the greenhouse and what are the costs?

Thank you for your help.

Washington County Oregon

1 Response

The information in quotes was used as a response to a previous inquiry from Multnomah County where winter conditions are essentially the same as in Washington County. I’ve added a few notes following that.

“To grow vegetables in a greenhouse through the winter, you do not need supplemental heating if you choose the right crops and plant them at the right time. To extend the season of summer crops like tomatoes and cucumbers far into the winter, you would need heating but also there is not enough natural light to grow a good crop in winter. Rather, you might plant cool season crops like aurgula, mustard greens, mache, and cilantro, which should be direct seeded or transplant lettuce, kale, and broccoli plants by mid-September.

“If you are looking for heating, there are propane heating units that mount on a 5-gallon propane tank, but with increased heat in a greenhouse, you will likely encounter pest (aphids and white fly) and disease problems and you will also need to vent the structure.”

Just how much additional heat would be needed, and the costs, will depend upon various factors, among them the source of the heat (electricity or gas) and its cost; the equipment used to supply to heat; also the prevailing temperatures outdoors.You will need to discuss the issues with your utilities provider.

As already mentioned, you would have to add heat in order to grow tomatoes,. But you would also need supplemental lighting because tomatoes require longer day length to grow and fruit than is naturally available during the winter. “Greenhouse Tomato”, a guide for Oregon commercial growers, will provide some insights: http://nwrec.hort.oregonstate.edu/tomatogh.html. And “Greenhouse Cucumbers” explains the details for that crop: http://nwrec.hort.oregonstate.edu/greenhouse.html.

More resources applicable to protected gardening during the winter:

- Planning and Planting Your Fall and Winter Garden (Includes basic information for winter gardening in a hoop tunnel, which is somewhat similar to using a greenhouse.) http://ext100.wsu.edu/skagit/wp-content/uploads/sites/5/2014/03/080511.pdf

- A Garden For All Seasons (Based on Eliot Coleman’s book.) provides a quick overview of a movable tunnel. http://umaine.edu/york/files/2014/02/garden_for_all_seasons.pdf

- Charley’s Greenhouse & Garden Supply, in Mt. Vernon. WA, lists several workshops on its web page : www.charleysgreenhouse.com/

- And you might check with your local library.

Bottom line: It will be much easier, also less costly, to grow quality cool season crops in the greenhouse than to attempt warm season crops such as tomatoes.