Hoophouse Update: Planting greens for winter harvest

September is the end of the harvest season for most Michigan gardeners, but, for me, it is also time to plant lettuces, spinach and other cold crops for winter harvest.

Sound crazy? Not since we put in our 26′ by 36′ hoophouse. Hoophouses are passive solar greenhouses that allow folks in Michigan to grow food all year round.

While others are winding down, I have been revving up, producing 22 trays of lettuce and spinach under lights indoors beginning in August. The plan is to stagger the planting during the late summer and fall.

Hoophouses do not allow you to grow warm weather crops like tomatoes during the winter. That’s asking too much. The solar energy from the sun heats the structure during the day, but the temperature plummets when the sun goes down because there is no supplemental heat source. Warm weather crops simply cannot tolerate frost.

But hoophouses provide enough protection from the wind and from the cold that you can build a year-round gardening strategy. Hoophouses allow you to plant earlier in the spring, which often means double-cropping during the summer. And if you time things right, you can establish cold crops in the fall and then harvest then all winter long.

Basically, during the winter, hardy plants thrive but grow very little, if at all. The benefit of the hoophouse is that it acts like a giant food locker. The plants will freeze solid overnight, but they thaw again during the day whenever there’s enough sun.

If you wait until the plants thaw completely, they are fresh and tasty when you pick them. (Harvest before they thaw completely, and they turn to mush.)

While the thermometer outside today struggled to break 50 degrees, it topped 80 degrees inside the hoophouse whenever the clouds parted.

The challenge is timing. I watered the new transplants and fed the earlier transplants with fish emulsion fertilizer. The beds were topped off with about two inches of high-quality compost. I want the crops established by the time hard frosts hit and the amount of sunlight declines, but fall has been a bit cooler than I had expected so far.

One surprise is that winter-grown hoophouse greens exhibit a different texture - they are almost silky. Tom Rumple of Whitmore Lake (see below), who raises greens year-round in his hoophouse for sale at the Ann Arbor Farmers Market, thinks that protection from the wind accounts for the different texture. He and I agree that hoophouse lettuce tastes wonderful.

If you want to learn more about hoophouse farming in Michigan, here are some videos I shot during the past year:

• Five hoophouse farmers share their stories - “Dahlia” Tom Rumple of Whitemore Lake; Kathy Fusilier of Manchester; Nic Welty of 9 Bean Rows Farm in Omena; Jimmy Spender of Pond Hill Farm in Harbor Springs; and Dale and Kami Moore of Engadine in the Upper Peninsula (the last video by Casey Williamson).
• Constructing Multi-Bay Tunnels for Organic Fruit Growing - A new series of high tunnels has been erected on the Michigan State University Student Organic Farm to study three-season fruit production under these protected structures. The video is narrated by Dr. Eric Hanson of MSU’s Department of Horticulture. On-going research on raspberries and fruit trees will explore the benefits, drawbacks and feasibility of growing fruit using these new structures.