High Tunnel Planting Scheduling – Working Out a Schedule for Successive Plantings

Rose Ogutu, Horticulture Specialist, Delaware State University rogutu@desu.edu

High tunnels offer flexibility in crop production and can handle diverse crops from asparagus to zucchinis and many crops in between. High tunnels create an environment, one hardiness zone warmer than the field. The only time not to plant is when daylight does not allow any growth at all, but one can schedule crops in high tunnel to continue all year long. Once day length exceeds 10 hrs per day in late January, seeding of plants in high tunnels can commence, especially with adequate soil temperatures (>55°F). The cropping system should take advantage of season extension while ensuring good use of high tunnel space. The capability of starting your own seeds or having a source of seedlings or planting material whenever needed is important. Growers involved in supplying their CSAs, local restaurants and wholesale markets are always thinking ahead and should develop a good successive planting schedule.

At this time high tunnel producers are done with winter production season and have moved on to spring production. In hind sight, and with this past winter season in mind, early planting and establishment of crops is very important. October 15 should be the latest fall planting date considered for winter harvesting. Having gone through a long, comparatively cold winter, some lessons have been learned. Provision of minimal supplemental heating during extreme cold situations and an inside layer of row covers help a great deal. During the winter months, one needs reliable production of spinach, lettuce, radish, carrots etc. Cultivars of these crops that may be tolerant of freezing temperatures should be considered. Part of the winter’s activities involves pulling out some fall plantings in January or February to open space for re-seeding. The crops to be removed could be lettuce, cilantro, Asian greens, claytonia, corn mache, kale or any other crops in the decline. End of winter and spring management of the high tunnel is often marred with uncertainties of what best to plant and plans for the main planting season.

Succession planting can continue in spring. Crops that could be planted between end of winter and summer include leaf lettuces, spinach, bulbing onions, spring carrots, cilantro, kale, baby chard, and arugula, which may reach maturity in the 12^th week window (May 1 to June 1). Tomatoes should be in the high tunnel by May 15. (The last day of frost in Delaware is May 1, but attention has to be paid to the weatherman.)

Summer high tunnel crops considerations. Temperatures in the hot summers soar high. Temperatures can rise well above 90°F and temperatures above 85°F reduce pollen formation in most crops. For the 2012 growing season, high tunnel temperatures at Smyrna Outreach and Research Center (DSU-SORC) averaged 12.0°F warmer than the outside air with the maximum averaging 18.3°F and the minimum averaging 5.2°F. Good ventilation depends on high tunnel design and orientation with regard to adequate air flow. Growers normally wonder about a summer high tunnel crop that will yield in a three-month window with an advantage of being grown inside, rather than in the field. Eggplants (oriental) and hot pepper tolerate the high temperatures. Use of shade cloth (30-50%) lowers air temperatures within the high tunnel by as much as 5 – 8°F. Shade fabric will reduce light intensity and air temperatures and reduce water and nutrient uptake by plants. Evaporative cooling with mist nozzles can be used to keep leafy greens cool.

Fall high tunnel production. A succession planting plan for direct seeded spinach or leaf lettuce in the fall, followed by transplanted heading varieties in the early spring can be used to achieve a nice, diverse crop offering. Carrots and scallions must be planted early in August to size up for winter. For success, crops should be seeded by October 1 or transplanted by October 15. Note that there are some fall plantings that can be left until the summer crop is planted. These are crops like spinach, parsley, dill, chamomile, chard, scallions, beet root, kale and leafy lettuce (var. Tango).

Cultivar suggestions are based on experiences from DSU-SORC and other high tunnel locations within Delaware. The cultivars are not a result of extensive comparison trials, other varieties can be considered with good or better results.

*Dates refer to approximate date of seeding, whether you are direct seeding or transplanting at a later date. Consider dates as ranges.

References
Amstrong and Neely Kynyon. Early Planting of Tomatoes in High Tunnel with Plant Coverings. http://www.ag.iastate.edu/farms/10reports/Armstrong/EarlyPlantingTomatoes.pdf