High Tunnel Planning and a Few Reminders for High Tunnel Tomato Growers

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

The cold months are over and you are probably thinking in terms of the major 3 planting cycles for your high tunnels: early spring, summer and early fall. It is always a good idea to prevent pathogens and insects from overwintering

Tomatoes still remain the number one crop in high tunnels in Delaware. Transplanting dates are approaching for growers who intend to hit the early market. Target the dates of transplanting to be 2-4 weeks before field planting. The average last frost dates are May 1 to May 10th. Seeding dates are normally 5 weeks prior to transplant dates. Transplants need to be hardened off before planting. If you are into growing grafted tomatoes, note that the grafting process will delay the seedling growth for 6 to 7 days, pushing your start date even earlier. Get in touch with your local Extension office for updates on varietal trials and recommended varieties. Local supplier of seedlings normally have great information and can provide guidance on choice of variety.

Varietal Selection
Your choice of variety is very crucial. Remember that the determinate varieties (60 to 75 days to maturity) are best for a quick early crop while indeterminate varieties produce all summer long. Determinate varieties form bush type plants that are more compact than indeterminate ones and are easier to support and contain. They ripen over a concentrated time period usually producing one or 2 main harvests. BHN 589, Primo Red, Scarlet Red and Mountain Fresh Plus are popular determinate varieties. There exist hundreds of tomato varieties in the market today. When choosing wisely, consider, yields, flavor, disease resistance and training needs. A number of varieties bred for greenhouse/high tunnel conditions also perform well in the open field conditions. Make the right choice because high tunnels have 20% less light than outdoors. As much as possible, avoid varieties with a vigorous growth habit and instead go for plants that have ‘tidy-growth habit which is more regular’, smaller leaves and fewer suckers.

High Tunnels help keep rain off the foliage, eliminating a number of fungal and bacterial diseases. Aphids, Spider mites, leaf mold, grey leaf spot and powdery mildew remain a challenge on sheltered tomato plants because of the high humidity and conducive temperatures. Verticillum, Nematodes, Fusarium, and Corky Root Rot are soil borne diseases which can be avoided by not growing on the same spot year after year. Problems associated with monoculture can be avoided by switching from growing in the soil to using media bags.

Other Considerations
For sturdy tomato plants, prepare a bed which is deep and well- draining. Spacing depends on varieties and trellising method. 30 inch raised inch raised beds can accommodate plants spaced 18 inches apart on Florida weave trellising- and double row spacing of 24 in staggered plants.

Always monitor plants in high tunnels. Close the high tunnels in the afternoon to capture peak heat. Consider using row covers to further protect plants from cold damage. Once nighttime lows are forecasted to be 50 °F or higher, leave the high tunnel open or vented to avoid unnecessary leaf moisture.

High tunnel tomatoes with row covers
Scouting an early tomato crop ‘BHN 589’ in a high tunnel in Sussex County. Note the additional protection from row covers.

Tomatoes have the best nutrient uptake when the soil pH is 6.2 to 6.5.

Avoid episodes of fruit cracking by managing irrigation well during fruit development.

Slower release fertilizers such as greensand as a potassium source and aragonite as a calcium source applied at plow down have demonstrated high potential to further reduce Blossom End Rot and Yellow shoulder.


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