In cooler climates, many blackberry farmers use a high tunnel to grow blackberries. A high tunnel is a hoop-house style of greenhouse with sides and end walls that can be opened to allow for ventilation to regulate the internal temperatures of the tunnel. It bridges the gap between larger, more expensive greenhouses and no protection at all. A high tunnel can extend the season for berry farmers in cooler climates, and increase the yield of berries produced. Growing blackberry bushes in a high tunnel is no more complicated than growing them in a greenhouse.
Select a site for your high tunnel that has the same growing conditions that berries grown without a tunnel require, which include loamy, slightly acidic soil with a pH of 5.5, full sunshine and good drainage.
Plant berries twice as far apart as berries grown without a tunnel system to guard against mold and other diseases caused by poor air circulation. According to Cornell University, a good space for berries in a house is 2 feet apart in rows that are 8 feet apart.
Select a tunnel frame based on your weather conditions. If you live in an area that receives heavy snowfall, choose a peaked-roofed tunnel. Areas less prone to snowfall are good for a hoop house frame-in.
Test soil moisture daily to determine the watering needs of your plants. You may need to water your plants via drip irrigation up to three times per week. Put your drip irrigation hose on a timer at the spigot to time the intervals of water use.
Fertilize plants with liquid fertilizer injected into the drip irrigation system. According to Cornell University, blackberries grown in a high house need approximately 100 ppm of liquid nitrogen fertilizer twice weekly.
Check the temperatures of your high house several times daily and adjust as needed. Temperatures in the high house can be lowered by opening the ends or rolling up the side walls to allow warm air to escape. In colder months, the plants can be covered with floating row covers to protect them against colder air.
Sink fence posts into the ground at the ends of rows and string wire down the length of rows to act as a trellis. Separate first- and second-year growth by tying blackberries onto a trellis into a fan shape. Place all first-year growth on one side, and second-year growth on another. At the end of each year, cut back the second-year growth to the ground. Tie new first-year growth into place on the trellis at the location of the previous year's second-year growth.