Penn State's high tunnel facility.
Growing tomatoes generates the greatest revenue per square foot and the quality of tomatoes produced in a high tunnel can be far superior to field grown fruit. However, the increasing numbers of tunnels and early tomatoes will likely reduce the current premium on early tomatoes. Growers should look at diversification to provide a wider range of product offerings and perhaps even give tunnel soils a break from tomato crop after tomato crop.
The controlled environment and season extension characteristics of high tunnels open up all kinds of opportunities for growers seeking to explore alternative production systems. High tunnel tomatoes are often superior to field grown fruit and generate more revenue per square foot than field grown tomatoes. Unfortunately, the constant production of tomatoes in high tunnels (with no rotation) has led to increased incidences of soil borne pathogens like verticillium and fusarium wilt. As a result, growers have been forced to move to grafted plants in order to maintain consistent production in these high tunnels.
Early tomatoes replanted
By planting tomatoes in a heated tunnel, growers in the Mid-Atlantic can install tomato transplants by early to Mid-April (or even earlier) and be harvesting by early June or earlier. If using an early fruiting, determinate variety such as Primo Red, there is the opportunity to remove the initial planting and replant in Mid-July with a variety such as Charger or Finishline for a September, October, November harvest. Indeterminate varieties such as Big Dena work well in an all season system. However, determinate varieties are often looking pretty poor by late summer. Replacing the plants in mid-July provides for fresh plants to carry into the fall while field produced tomatoes are in good supply. Replacement transplants will need to be started in early June for this system. Due to variations in varieties sensitivity to day length, not all tomato varieties will work when mid-summer planted.
Early tomatoes replaced with parthenocarpic cucumbers
This variation on the system noted above simply replaces the early tomatoes with parthenocarpic cucumbers in mid-July. Since the cucumbers develop so quickly as compared to tomatoes, this plant flip can be delayed until late-July or early August while still yielding a substantial crop. Plants and stakes will need to be removed, but drip tape and plastic mulch can be reused. We've had excellent success with cucumbers when planted in the mid to late summer period with harvest occurring into late October in an unheated tunnel. With a bit of heat, there is the strong possibility to carry summer planted cucumbers into mid-November or later. Consider varieties such as Corinto, Lisboa, Picolino, Katrina or Socrates. Plan ahead to manage powdery mildew and botrytis. Cucumbers develop very quickly so this is a very fast turnaround crop to maintain cash flow. Direct plant cucumber seeds 6" apart and train vertically using vine clips and heavy tomato twine. By screening the tunnel with regular window screening, you can prevent cucumber beetles and have higher quality cucumbers by keeping pollinators away.
Green then colored: Two of the challenges with bell peppers are the very low prices during the summer glut of green field bells and the high losses in the field if fruit are left hanging long enough to color fully. Growing bell peppers in a high tunnel beats both of these problems. Green bells will be in full harvest 4-6 weeks prior to field bells and the typical 80-90% packing losses for bells left to color in the field can be reversed to where growers can pack 90% or better of red, yellow or orange peppers from a tunnel. Consider dividing production so that a portion of the plants are harvested as green bells as early as possible while allowing others to hang until fully colored. Then when field green bells begin to show up and prices drop, stop picking them in the tunnel and allow them to color completely. Be proactive in managing our latest bell pepper pest, Broad mites. This pest appears to be gaining ground rapidly and can decimate pepper plants and fruit.
Early tomatoes then greens into fall
Take advantage of the higher prices for early season tomatoes, then flip production to produce greens when the prices for tomatoes start to dip. One of the challenges with replanting tomatoes mid-summer is that you'll probably be removing plants with lots of potentially marketable fruit. If replanting the tunnel with greens instead of tomatoes, you can delay the replant for several weeks and potentially have greens to sell all winter. Transplants can go into the same plastic that the tomatoes came out of or plant into flats filled with potting media that are installed over the beds propped up on concrete blocks for easier harvesting.
Succession plantings of parthenocarpic cucumbers
The quality of cucumbers that come out of high tunnels can be extraordinary as compared to field grown. Once your markets get used to these beautiful cukes, it may be hard for them to accept field grown. Rather than planting an entire tunnel at the same time, consider planting in flights every 2-3 weeks, so that there are always young plants coming into harvest all season. So long as no soil-borne diseases crop up, there is no reason not to remove and replace plants as they senesce naturally during the season. Experience at the Penn State Southeast Agriculture Research and Extension Center (SEAREC / Landisville Farm) over the past three years has shown us that cucumber vines start to naturally senesce after 5-6 weeks of harvesting. We grew the cucumbers in #2000 (3.6 gallon) nursery pots with two plants per pot. As the vines started to collapse, we simply removed the plant roots and all, topped off the pot with fresh potting media, direct seeded and were back in production in 40-45 days.
Day neutral strawberries
By tunnel growing day neutral strawberries, harvest can begin well ahead of the June field season, continue slowly all summer, then rebound in the fall. Consider planting into containers using a high percentage coir potting media or coir planting strips on stepped benches to make the best use of space and reduce stoop labor. Monitor nutrients carefully as coir planted berries will often be calcium challenged. When using any media other than soil, the system is a variation on hydroponic production, so the crop is completely dependent on proper fertigation. Scout often for Spotted Wing Drosophila (SWD) and mites.