Q&A

DEAR NEW FARM:

I have space to put up a gothic-style greenhouse, but it will only be able to run north to south. Will I have any problems with enough light coming in to grow cold-hardy crops in the winter.

Thanks,
Mike Bollinger
Illinois

DEAR MIKE:

We asked our friend Darrell Frey, proprietor of Three Sisters Farm (www.bioshelter.com), for some assistance with your question. Here’s what Darrell had to offer:

“Assuming you mean a greenhouse glazed on all sides, the orientation is not as critical as you may think. The shape of your property, available level ground, drainage and best orientation for the most sunlight (no trees or buildings blocking light) all help determine placement. The high tunnels at Penn State's High Tunnel Research Facility all run north to south, with the roll-up sides facing east and west. This allows for full ventilation by prevailing winds when the sides are up.

At Three Sisters Farm we orient our 16-foot by 45-foot high tunnels east to west, partly because the garden contour lines run that way, and partly because our tunnels have no roll-up sides and so are ventilated by the wind passing through them lengthwise.

With either orientation, productivity is not affected if light enters from all sides.

If you have a greenhouse that is only glazed on one side, orientation north and south will greatly reduce productivity. Variation to the east or west of solar south by 20 degrees reduces solar gain by 5 percent. Variation by 30 degrees reduces gain by 10 percent. The numbers seem small but can become significant relative to heat gain and plant growth, so any orientation over 30 degrees away from true south is to be avoided. When a building is oriented 45 degrees from true south, solar gain is reduced by more than 25 percent. Certainly a north-south orientation would reduce light by 50 percent if one side is not glazed. Be sure to glaze the south-facing endwall well. If you are also plagued by lake-effect clouds, orientation away from full sunlight is especially critical. In areas with plentiful winter sun, the difference may not be as important.

Darrell Frey
Three Sisters Farm
Pennsylvania

NF

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