At the end of last year (2013) we conducted two winter trials on specific types of Lettuce, Greens, and Herbs at our Research Farm in Albion, Maine. Steve Rodrigue, the Johnny’s Product Technician who oversaw the trials, summarizes the process below:
The overwintering trials took place in two of our caterpillar tunnels at the Johnny’s Farm. The caterpillars we used were slightly different from those we offer via the catalog and online, because they have both end walls and side roll-up walls. With roll-up walls, we were able to ventilate much more throughout the trial - until the snow eventually prevented us from doing so. We had several small trials happening in the tunnels, which included Salanova Lettuce, Baby Leaf Lettuce, Greens, Spinach, and Cilantro.
The Salanova performed very well and lasted into the New Year. For that trial, we had two different seeding dates at two weeks apart. The earlier seeding allowed for the plants to grow to a marketable size whereas the later seeding and transplanting did not mature before going into the Winter. This is another indication of how important it is to experimenting with several seeding dates.
We had some issues with Bottom Rot with the Salanova, but we felt that was due to inadequate ventilation. Moving forward with our future overwintering trials, temperatures will be monitored several times throughout the day in order to best time the removal of the inner covers (agribon). Also, while the caterpillars did a fair job at protecting the crops through the harsh winter, we found them to be more of a challenge for adequate temperature regulation than a Hoophouse or High Tunnel. The short height and smaller volume of the Caterpillar Tunnel results in much larger fluctuations in temperatures, which means you have to do a lot more regulating of the temperatures.