Rose Ogutu, Horticulture Specialist, Delaware State University rogutu@desu.edu
Are your High Tunnel Side Vents still open during fall production?
Fall temperatures in Delaware (2012 USDA hardiness zone-7A) are characterized by falling temperatures (Table 1). Although we have not documented the average high tunnel temperatures during these months, it is commonly agreed that whether your high tunnel is single or double poly covered, they are above the temperatures listed in Table 1.The Fall season is less than 60 days long and high tunnel growers go for quick maturing cool season crops, some of which are suggested in Table 2.
Table 1: Average Fall months’ temperatures (°F) in Delaware, based on weather data collected from 1981 to 2010 by National Oceanic and Atmospheric Administration (NOAA) National Climactic Data Center.
| September | October | November | December | |||||
| High | Low | High | Low | High | Low | High | Low | |
| Dover | 79 | 60 | 69 | 49 | 59 | 40 | 47 | 31 |
| Georgetown | 78 | 59 | 68 | 47 | 58 | 39 | 48 | 30 |
| Lewes | 79 | 63 | 69 | 52 | 59 | 43 | 49 | 34 |
| Milford | 78 | 57 | 68 | 46 | 58 | 37 | 47 | 29 |
| Newark | 80 | 57 | 69 | 45 | 58 | 36 | 46 | 28 |
| Wilmington | 77 | 58 | 66 | 46 | 56 | 37 | 45 | 29 |
High tunnels make a difference. Inside and outside the high tunnel in Hartly Delaware on Oct15, 2012
Tips for Managing Your High Tunnel in the Fall
Avoid over-applying nitrogen. High N-levels keep plants soft and less hardy. Various stresses and health conditions can also lessen hardiness.
Beware of extreme cold forecasts. Roll down the high tunnel sides and make sure your high tunnel is not letting in cold fronts. The use of floating row covers and hoop supported row covers is highly recommended to help reduce heat loss by convection thus maintaining higher temperatures within the high tunnels. Overhead irrigation using micro sprinklers prevents frost damage. It is important to remember not to irrigate before cold spells as water stress enhances frost tolerance.
What about pests in fall? Although most major pests have cycled out by the fall season, the relatively warmer temperatures in the high tunnels can be a hub for pests and they can thrive and need to be managed. When using biological control, avoid using chemicals. Put in place yellow and/or blue sticky cards just above the plants to monitor pests. Keep up with good sanitation in the high tunnels, removing weeds and diseased or unwanted plant material.
Table 2: Suggestions for high tunnel fall and winter production
