The Fruit Growers News

Research underway at the University of New Hampshire (UNH) would allow northern growers to harvest ripe strawberries early in May, nearly five weeks ahead of field grown fruit.

The UNH project aims to demonstrate how earliness can be improved by growing berries in plastic tunnels with a “bleacher,” or tiered, planting system. This technique is a spin-off of the annual hill system which encourages growers to plant berries in the field on raised beds covered with plastic.

Otho Wells, now retired, first introduced the concept of growing berries in tunnels in the region, while on staff with UNH Extension. This technique brought berries in several weeks early, offering growers the chance to capture market premiums for early fruit. However, a “yield barrier” due to the limitations of the tunnel size put a cap on profitability.

To boost the harvest, William Lord, UNH Extension fruit specialist, has adopted the bleacher, system of planting that allows growers to increase the plant density in the tunnels. Berries planted on flat ground in tunnels were set at a spacing of about 2.5 to 3.5 square feet per plant. With the concentrated bleacher system, the spacing requirements shrink to 3/4 to one square foot per plant.

The experimental growing technique is being studied in a 12 foot-by-40 foot plastic tunnel. Lord described his current project and future goals at a recent UNH field meeting held on campus in Durham.

In order to maximize the heat from winter sun, the tunnel is sited with the ends facing east and west, rather than north and south. One half of the tunnel is then outfitted with stairstep shelving to accommodate berry plants grown in long plastic bags. In the other half of the tunnel, the bags are laid flat on the ground to eliminate shading of the berry bags on tiers.

This year, two sizes of berry bags were used, both an eight-inch width and a 10-inch width. The bags arrive as white-on-black plastic, but Lord reversed some to see if black-on-white had a positive impact on plant growth and yield. The bags were filled with a conventional soilless growing media and the young plants were planted in bags during the first week of October 1999. In past experiments, the berries were ready for harvest the following spring, around May 1. This year, the crop is running one week later. At the field day, which was held May 9, ripe berries were set to be harvested in 24 hours.

During this year’s study, Lord grew the strawberry plants under three different heating regimes: no bottom heat, minimal bottom heat (enough to keep the soil bag from freezing), and high bottom heat (enough to maintain a temperature of 45&Mac251; through the nigh).

At this stage in the project, Lord has identified two important results. From temperature data collected through the winter, Lord concludes that the best bag color for growing in tunnels is black-on-white.

“The black bags are best because they resist absolute cold penetration. When you compare the temperature in the black bags (no bottom heat), to the temperature in the white bags (no bottom heat), the black bags held their heat better and the temperatures of the growing media always ran five degrees higher than the white bags,” said Lord.

Experiment results also suggest that high bottom heat should be avoided. In the UNH study, the bags with high bottom heat saw the temperature of the growing media spike to 105&Mac251;, a level that could damage plant tissue. In addition to excessive heat, the high temperature led to pest problems. Aphids and two-spotted mites survived and multiplied in the bags with high bottom heat, making pesticide applications necessary.

John McLane, UNH Woodman Farm manager, says, “One application of Brigade knocked down the mite problem, but hot spots persist. A follow-up application of Vendex may be necessary.”

The pest problems surprised the UNH staff, since they have grown berries in tunnels for five years and applied few pesticides.

“In past trials, we have harvested berries grown in a spray-free environment. This is a growing practice that can translate into a marketing advantage at harvest time,” said Lord.

When the blossoms were open early this spring, the bees were not active enough to achieve good pollination. This year’s harvest includes a greater proportion of misshapen fruit due to poor pollination.

“In the future, it will be standard practice to place pre-packaged bees in the tunnels,” Lord says.

Chandler is the variety used in the UNH tunnel trials. To date, this variety has been the highest producer with average fruit size weighing 3/4-ounce. The flavor has been judged to be excellent. Throughout the research trial, the berries were fertilized three times with a foliar feed and watered as needed.

Future trials will focus on trying to identify the best growing media for berries in tiered tunnels. A $1,000 grant from The New England Vegetable and Berry Growers Association was recently awarded to help support these upcoming studies.

Lord said continued research is needed before he could recommend the bleacher system to growers. According to his figures, he thinks startup costs can be covered in one year, but his goal is to shrink these production costs and generate a practice that leads to greater profits.

A simultaneous study underway monitors berry production in two plastic tunnels. These plants growing on the flat ground covered with black plastic yield ripe berries a few weeks before conventional matted row berries.

The objective of one research trial with tunnel berries is to encourage the plants to set more flower buds and subsequently yield more fruit. Reflective row covers are used to encourage the plant to set more flowers. The covers with an aluminum reflective type exterior and black interior, reduce the plant’s exposure to light and creates a short day. The plant’s response to the short day environment is to set flowering buds. The reflective covers were used from March 15 through May 1.

“We observed a number of positive results from this practice, including picking 20% more fruit per plant during the primary June harvest period,” said Lord.

The plants also tended to be shorter, which made it easy to pick fruit, and there were fewer runners. The flower buds set in March and April, due to the reflective covers, mature into berries between July 10 and Aug. 1. Yields with this summer fruit are small and excessive heat can make the fruit soft. Future studies will try to overcome these obstacles.

While growers wait for more information on berries in plastic tunnels, many have given a thumbs up to the outside annual hill system. This method contributes to earlier harvests and keeps weeds in check, In one UNH trial, Lord overwinters the berry plants under a floating row cover instead of conventional organic mulch. He aims to prove that when plants are protected from cold but exposed to light, they develop into stronger plants within a greater amount of stored carbohydrates that can be used later during fruiting. With the annual hill system, live plug plants go in the ground Sept. 1 and are harvested the next spring.

“If you delay and plant after Sept. 1, the yield reduction is substantial,” cautions Lord.

For more information on growing strawberries in plastic tunnels or in the field with the annual hill system contact Lord at (603) 862-3203 or e-mail william.lord@unh.edu.



		These New Hampshire Strawberries are No Bleacher Bums By Melissa Moore New England Correspondent Research underway at the University of New Hampshire (UNH) would allow northern growers to harvest ripe strawberries early in May, nearly five weeks ahead of field grown fruit. The UNH project aims to demonstrate how earliness can be improved by growing berries in plastic tunnels with a “bleacher,” or tiered, planting system. This technique is a spin-off of the annual hill system which encourages growers to plant berries in the field on raised beds covered with plastic. Otho Wells, now retired, first introduced the concept of growing berries in tunnels in the region, while on staff with UNH Extension. This technique brought berries in several weeks early, offering growers the chance to capture market premiums for early fruit. However, a “yield barrier” due to the limitations of the tunnel size put a cap on profitability. To boost the harvest, William Lord, UNH Extension fruit specialist, has adopted the bleacher, system of planting that allows growers to increase the plant density in the tunnels. Berries planted on flat ground in tunnels were set at a spacing of about 2.5 to 3.5 square feet per plant. With the concentrated bleacher system, the spacing requirements shrink to 3/4 to one square foot per plant. The experimental growing technique is being studied in a 12 foot-by-40 foot plastic tunnel. Lord described his current project and future goals at a recent UNH field meeting held on campus in Durham. In order to maximize the heat from winter sun, the tunnel is sited with the ends facing east and west, rather than north and south. One half of the tunnel is then outfitted with stairstep shelving to accommodate berry plants grown in long plastic bags. In the other half of the tunnel, the bags are laid flat on the ground to eliminate shading of the berry bags on tiers. This year, two sizes of berry bags were used, both an eight-inch width and a 10-inch width. The bags arrive as white-on-black plastic, but Lord reversed some to see if black-on-white had a positive impact on plant growth and yield. The bags were filled with a conventional soilless growing media and the young plants were planted in bags during the first week of October 1999. In past experiments, the berries were ready for harvest the following spring, around May 1. This year, the crop is running one week later. At the field day, which was held May 9, ripe berries were set to be harvested in 24 hours. During this year’s study, Lord grew the strawberry plants under three different heating regimes: no bottom heat, minimal bottom heat (enough to keep the soil bag from freezing), and high bottom heat (enough to maintain a temperature of 45&Mac251; through the nigh). At this stage in the project, Lord has identified two important results. From temperature data collected through the winter, Lord concludes that the best bag color for growing in tunnels is black-on-white. “The black bags are best because they resist absolute cold penetration. When you compare the temperature in the black bags (no bottom heat), to the temperature in the white bags (no bottom heat), the black bags held their heat better and the temperatures of the growing media always ran five degrees higher than the white bags,” said Lord. Experiment results also suggest that high bottom heat should be avoided. In the UNH study, the bags with high bottom heat saw the temperature of the growing media spike to 105&Mac251;, a level that could damage plant tissue. In addition to excessive heat, the high temperature led to pest problems. Aphids and two-spotted mites survived and multiplied in the bags with high bottom heat, making pesticide applications necessary. John McLane, UNH Woodman Farm manager, says, “One application of Brigade knocked down the mite problem, but hot spots persist. A follow-up application of Vendex may be necessary.” The pest problems surprised the UNH staff, since they have grown berries in tunnels for five years and applied few pesticides. “In past trials, we have harvested berries grown in a spray-free environment. This is a growing practice that can translate into a marketing advantage at harvest time,” said Lord. When the blossoms were open early this spring, the bees were not active enough to achieve good pollination. This year’s harvest includes a greater proportion of misshapen fruit due to poor pollination. “In the future, it will be standard practice to place pre-packaged bees in the tunnels,” Lord says. Chandler is the variety used in the UNH tunnel trials. To date, this variety has been the highest producer with average fruit size weighing 3/4-ounce. The flavor has been judged to be excellent. Throughout the research trial, the berries were fertilized three times with a foliar feed and watered as needed. Future trials will focus on trying to identify the best growing media for berries in tiered tunnels. A $1,000 grant from The New England Vegetable and Berry Growers Association was recently awarded to help support these upcoming studies. Lord said continued research is needed before he could recommend the bleacher system to growers. According to his figures, he thinks startup costs can be covered in one year, but his goal is to shrink these production costs and generate a practice that leads to greater profits. A simultaneous study underway monitors berry production in two plastic tunnels. These plants growing on the flat ground covered with black plastic yield ripe berries a few weeks before conventional matted row berries. The objective of one research trial with tunnel berries is to encourage the plants to set more flower buds and subsequently yield more fruit. Reflective row covers are used to encourage the plant to set more flowers. The covers with an aluminum reflective type exterior and black interior, reduce the plant’s exposure to light and creates a short day. The plant’s response to the short day environment is to set flowering buds. The reflective covers were used from March 15 through May 1. “We observed a number of positive results from this practice, including picking 20% more fruit per plant during the primary June harvest period,” said Lord. The plants also tended to be shorter, which made it easy to pick fruit, and there were fewer runners. The flower buds set in March and April, due to the reflective covers, mature into berries between July 10 and Aug. 1. Yields with this summer fruit are small and excessive heat can make the fruit soft. Future studies will try to overcome these obstacles. While growers wait for more information on berries in plastic tunnels, many have given a thumbs up to the outside annual hill system. This method contributes to earlier harvests and keeps weeds in check, In one UNH trial, Lord overwinters the berry plants under a floating row cover instead of conventional organic mulch. He aims to prove that when plants are protected from cold but exposed to light, they develop into stronger plants within a greater amount of stored carbohydrates that can be used later during fruiting. With the annual hill system, live plug plants go in the ground Sept. 1 and are harvested the next spring. “If you delay and plant after Sept. 1, the yield reduction is substantial,” cautions Lord. For more information on growing strawberries in plastic tunnels or in the field with the annual hill system contact Lord at (603) 862-3203 or e-mail william.lord@unh.edu.












The Fruit Growers News website offers a sampling of articles and features from each month. Subscribe to get all the news offered in The Fruit Growers News delivered right to you home! Permission is granted for reprinting material, except for commercial or advertising purposes, provided The Fruit Growers News is given full credit.


	Copyright 2000 Great American Publishing, Inc. The Fruit Growers News 343 South Union Street - PO Box 128 - Sparta, MI 49345 Phone 616-887-9008 - Fax 616-887-2666 - email All Rights Reserved