The production of raspberries in greenhouses for winter sales is an idea that has captured the attention of New England fruit growers since hearing about it from Cornell researcher Dr. Marvin Pritts at the New England Vegetable and Berry Growers Conference and Trade Show in 1997. In his presentation entitled "Raising Cane: Winter Raspberries for Northern Climate", Dr. Pritts introduced a system for planting tissue-cultured, summer-fruiting raspberries in 1-gallon pots. He recommended using a simple potting mix, maintaining the plants outdoors for the summer months using a drip irrigation system, then moving them into the greenhouse in mid-December after a required period of chilling had been satisfied. Once in the greenhouse the plants brake dormancy, flower in about six weeks and produce ripe fruit in 10 weeks. The harvest period lasts for about 8-10 weeks, from late February to early May.
The appeal of this system toNew England growers is several-fold. First, and foremost, is the high price that raspberries fetch in the marketplace at this time of year. Typically, retail outlets offer raspberries during the winter months that are shipped from Chile and Mexico at a cost to consumers of $4.00 - $6.00 per half pint. No domestic sources of raspberries exist at this time of the year. The quality of the imported fruits is usually low due to the perishable nature of raspberries and the distance traveled before reaching the consumer. Never-the-less, consumers apparently will accept this reduced quality and high price. The second appeal of this system is its simplicity. Raspberry plants have a relatively low chilling requirement (1000+ hrs below 45˚F) so can be moved into the greenhouse early in the winter (mid December). Also, they prefer cool growing temperatures (55˚F – 70˚F) so the cost of heating is less than for some other greenhouse crops, and they do not require supplemental light in order to produce profitable yields.
A third appeal is the advantage of producing fruit in a controlled environment where the above ground portion of the plant is not subjected to wetting by rain or dew. Irrigation water is delivered to the roots via a drip system, which can also be used to deliver fertilizer. This significantly reduces the threat posed by many of the disease problems that affect raspberries grown outside such as cane blights and fruit rots. In addition, many of the insect pests that are active in the summer months are simply not present during this winter production window. However, this system is not without some pest management challenges. Two-spotted spider mites and powdery mildew can both become problems in greenhouse environments. The good news is that there are both low-spray and biological options for managing these problems so the potential for organic production is realistic.
One barrier to this system until recently was the problem of pollination. Hand pollination was far too labor intensive, and honeybees were poorly adapted to greenhouse use. With the advent of commercial bumblebee production, this barrier was removed and Dr. Pritts saw an opportunity to develop a system for greenhouse production of raspberries. After several years of research, this system has been developed to the point where its is ready for on-farm testing to see if it can live up to the promise is seems to hold.
Putting the System into Practice
Hamilton Orchards, in New Salem, Massachusetts, is a typical New England farm with a range of crops raised. They grow a variety of tree fruit, (apples, peaches, plums, Asian pears) and small fruit (strawberries, summer and fall raspberries, blackberries, blueberries). They also have a commercial kitchen and dining area combined with a retail stand and offer value-added products (preserves, baked goods, etc.) in addition to their fresh fruit for sale in a variety of ways (i.e., wholesale, retail, farmers market, and pick-your-own). Greenhouse raspberry production offered an opportunity for season extension for a crop they were already familiar with.
With the support of some grant funding from the Department of Food and Agriculture's Agro-Environmental Technology Program, technical assistance from UMass Extension, and the investment of a lot of personal resources and ingenuity, Bill Hamilton set out to see for himself if this system could work for his farm. In the spring of 2000, 900 bare-root raspberry plants (600 'Tulameen' and 300 'Encore') were planted into pots and set up in neat rows with trickle irrigation supplying them with water and fertilizer. There they grew throughout the summer, each producing 2-3 primocanes 3-5' long. A site for a new 72' x 34' greenhouse was leveled and prepared for construction. An additional 300 dormant bare-root, long-stem 'Tulameen' plants were ordered from Washington State to compare with the ones grown from traditional nursery stock.
With completion of the greenhouse construction delayed until early January 2001, Bill was not able to move plants into the greenhouse until about a month later than planned, about January 20th, 2001. This meant that the pots had to be moved into protective cold storage in order to prevent cold damage. This was an unexpected and labor intensive step. Fortunately, space was available in an empty refrigerated apple storage room so that the temperature could be controlled at 35˚F until the greenhouse was ready. The procedure for bringing the long-cane plants out of dormancy was more complicated than the tissue cultured plants, which were simply moved directly into the greenhouse.
The long-canes stayed in the cold storage and the temperature increased by 5˚F/week for 4 weeks before moving them into the greenhouse. Controlled temperature storage is more important when using the fall dug dormant long-cane plants because they require a systematic acclimation to growing temperatures in order to develop normally.
Once in the greenhouse, daytime temperatures were maintained at 65˚F during the day and 55˚F at night. As the foliage began to emerge and expand, weekly pest scouting began. A total of 788 pots (506 'Tulameen', 164 'Encore', and 118 long-stem 'Tulameen') were moved into the greenhouse. Extra pots remained in the cold storage and were moved out-doors in the spring.
Six weeks after moving the plants into the greenhouse, they began to show swelling flower buds. It was time to bring in the bumblebees. At the same time, pest scouting revealed the presence of first, two-spotted spider mites and later, European red mites. These pests were found first among the long-cane plants and later spread throughout the greenhouse. Since bumblebees were being introduced into the greenhouse at this time, insecticide/miticide sprays were out of the question. The first hive was moved in on March 13th. The following day, a release of predatory mites (a combination of Neoseiulus fallacis and Phytoseiulus persimilis) were released to control the infestation of pest mites. A follow-up release of predators was made one month later and the pest mites never reached damaging levels.
As the pollination period progressed, a second unanticipated problem emerged. It began to appear that the bumblebees were not pollinating the flowers evenly. Misshapen fruit were developing as though flowers were only partially pollinated. At first we thought that we had insufficient numbers of bumblebees and brought in a second and later a third hive. When the uneven pollination persisted, we looked for other factors. After installing recording hygrothermographs to monitor temperature and relative humidity simultaneously, we concluded that the low night temperatures were causing high humidity (100%) in the greenhouse for 10 – 14 hours each 24-hr cycle. This was causing the pollen to become too 'sticky' to be adequately transferred by the bees. The problem was partially resolved by simply increasing the temperatures by 10˚F at night. In the long term, it may be necessary to install a concrete floor in the greenhouse to reduce the amount of moisture coming from the ground under the greenhouse. The Cornell research had not encountered this problem because it was all done in glass houses with concrete floors where humidity is typically very low. So low, in fact, that supplemental humidity had to be provided in order for pollen, once transferred, to germinate.
Another humidity related problem emerged in the harvest phase of production and that was the development of powdery mildew infections on the leaves and Botrytis cinerea fungal infections of the canes. Again, these problems were reduced mainly through the increase of night-time temperatures to lower the humidity in the greenhouse.
The first fruit were picked on April 15th (6 weeks from the beginning of bloom). A total of 2,087 1/2 pints of high quality fruit were harvested from the 788 plants for an average of 2.64 half-pints per plant. This is similar to the yield achieved in the Cornell trials. Higher yields (50 – 60%) could have been achieved if the pollination problem had been anticipated. The Cornell trials suggest that yields of 8 – 11 half-pints per plant in the second and third year of production can be expected.
All harvested fruit was sold at a consistent price of $42/flat of 12 half-pints. This equals $3.50 per harvested half-pint for a total income of $7,304.50. This translates to $2.98 per square foot of greenhouse space. If projected yields of 8 – 11 half-pints are achieved in subsequent years, returns would increase to approximately to over $9.00 per square foot of greenhouse space. In 2001, peak harvest were the weeks of May 6th and May 13th when over 530 half-pints were picked each of those weeks. The highest yield was achieved by the own-grown, bare-root 'Tulameen' plants. These plants produced 25% more marketable fruit than the long-cane plants or the own-grown 'Encore' plants.
Economics of the System
Table 1. Production costs for the first year of
greenhouse raspberry production.
|Item||Cost per pot|
Potting mix and pots
|Drip irrigation/fertigation system||$0.60|
The profitability of this system hinges on the cost of producing the fruit. In this case, the cost for establishing this crop was high, especially since the farm had no existing greenhouse to use. A farm with an existing greenhouse will have a distinct advantage in establishing this system. However, costs beyond that of constructing the greenhouse came to approximately $11.70 per pot (Table 1). The costs included plants and potting material, irrigation supplies, bumblebees and mite predators, trellis support, harvest supplies, and production and harvest labor. Income received from the system (based on harvesting 2.64 half-pints per pot and receiving $3.50 per half-pint) was $9.24 per pot. As you can see, in the first year of this project, returns did not meet the costs. However, you may also remember that the pollination problems reduced marketable yield by approximately one third. The key to profitability of this system is the expected yields in the second and third years where returns are expected to be 8 – 11 half-pints per pot (or $28 - $38 per pot). The cost of production in these years will be similar to that of the initial year. Plants costs will be lower but potting material costs and harvest costs will be slightly higher. The number of pots contained in the greenhouse will be lower because the size of the pots will be larger.
The economics of this project were, while only marginally successful, still quite promising. The Hamiltons identified several 'fixable' problems. First, solving the pollination problem should increase yields by approximately 50%. Second, concentrating primarily on bare-root 'Tulameen' plants (which yielded the highest) will increase the over-all profitability on a square-foot basis. Finally, knowing that the yield increases significantly in the second and third years of production makes the investment in the first year more acceptable.
The goal of this project was to 'test drive' this system in the real world and see if it might offer an appealing option for Massachusetts producers. Knowing that it performed well under adverse conditions, suggests that it might work even better for those whose initial investment doesn't need to be so high. That is, producers who already have existing greenhouse space that can be put into this production system. The market is very large and can accommodate many local producers. One remaining challenge will be the efficient marketing of this product. For the Hamiltons, one of the most unrewarding elements of the system was having to drive around to many buyers and sell only a few flats at a time. While all the fruit was sold, the time spent driving from one buyer to another was not very efficient. This problem may increase as more people get into this production system. An efficient wholesaling system that doesn't erase the profit margin for small scale local producers will make this production system take off.