Although high tunnels make it possible for Indiana farmers to grow vegetables year-round, many growers may choose to end the production season in the fall. After a busy summer, it is not unusual that off-season management is overlooked. Nevertheless, these good management practices determine the success of the next year. It is an old lessen, but we can never put too much emphasis on the importance of good management practices during the off-season.
- Terminate plants after final harvest, and remove crop residues out of the tunnel. The worst scenario I have ever seen was a high tunnel full of weeds in late fall, and a few tomato plants still standing in the middle of the weeds. No doubt, the plant materials provide a cozy environment for insect pests to survive the winter. Under the ground, the roots of tomato plants, as well as roots of several weeds continue to feed plant parasitic nematodes, helping them survive the winter. It is not difficult to imagine that all the pests are ready to multiply and attack the new crop when it is planted next year. The best practice is to terminate crops after final harvest as soon as possible. Clean all the leaves, stems, dropped fruit, and pull up plant roots as far as you can. As Dr. Dan Egel always says, remove the plant residue as far away from the high tunnel as possible. Not only the plant materials, but also the trellises system like tomato stakes should also be removed and sanitized.
- Keep high tunnel open during the coldest time of the winter. The idea is to allow low temperatures to kill pests. It is true that the lowest temperature inside the high tunnel is not that much different as the lowest temperatures outside. A closed high tunnel can bring temperatures back quickly after the sun is up. Keep in mind that not just the threshold temperature, but also how long the pests are exposed to the threshold temperatures kill pests. When the tunnels are open, do not forget to watch for strong winds.
- Expose soil to natural rain and snow. If it is time to change plastic, do this during the off-season, and allow plenty time before installing the new plastic, so the natural rain and snow can wash excessive salt off of the top soil. If you do not have a plan to change the plastic, there is still chance to get a decent amount of snow covering the soil if the sides of the high tunnels are wide open.
- Adjust soil pH if it is needed. Out-of-chart soil pH leads to many problems in crop production, while it is one of the most difficult issues to be addressed during the growing season, especially for organic production. Due to irrigation water quality, we saw a trend of increased soil pH in the high tunnel after multiple years of crop production in Indiana. If this happens, you may want to consider adding sulfur to bring soil pH down. The general rule is to add 2 lbs elemental sulfur per 100 square feet to bring soil pH from 7.5 to 6.5 depending on soil types. The way sulfur works is through a biological process: bacteria in the soil converts elemental sulfur to sulfuric acid, which reduces soil pH. Because microorganisms are involved, soil conditions such as temperature determine how effective this process is, and the conversion process takes time.
Last note, vegetables differ in their sensitivity to high salts and high pH. Among the most widely grown crops in high tunnels, tomatoes in general are more tolerant to adverse soil conditions than cucumbers and peppers. That’s probably why growers may not realize they have soil problems until they start to grow cucumbers and peppers in a high tunnel that used to grow tomatoes.