Growing Winter Raspberries 

 in a Greenliouse 



Marvin P. Pritts 



Department of Horticulture, Cornell Universit}', Ithaca, NY 



Navigating snowy, ice-covered roads on the way to mar- 

 ket IS among the challenges facing a new type of raspberry 

 grower. A few innovative producers are harvestmg up to 60 

 flats (720 half-pints) of fresh raspberries from a 20 X 30 ft. 

 house between February and May, and selling them for 

 $2,000. Greenhouses have been used for many years to pro- 

 duce tomatoes and cucumbers during winter, but these veg- 

 etables require relatively warm temperatures and high lev- 

 els of light, makmg their production expensive. Raspber- 

 ries, however, are uniquely suited for greenhouse produc- 

 tion during the off-season. They grow best at cool tempera- 

 tures (60 - 70°F) and do not require supplemental light to 

 produce a crop, especially if production is targeted for May 

 and June. In northern states, many greenhouses are empty 

 during the winter months, but these could be used to grow 

 raspbemes with only moderate inputs, providing greenhouse 

 owners with an opportunity to produce an extremely high 

 value crop during a time of the year when they are realizing 

 no return on their capital investment and when no domestic 

 raspberries are available. 



The vast majority of winter raspberries currently on the 

 market are flown in from the Southern Hemisphere. Quality 

 is generally poor, because raspberries have an extremely 

 short post-harvest life and bruise easily during shipping. As 

 a result, consumers are willing to pay between $3.00 and 

 $6.00 per half-pmt for fresh fruit of superior quality, and 

 restaurant chefs seem willing to pay even more. 



Local raspberry production is now possible because of 

 two accomplishments in the area of entomology. First, 

 bumble bees have now been domesticated and are available 

 in small hives for pollinating greenhouse crops. Bumble 

 bees perform better than honey bees in greenhouses, espe- 

 cially under the cooler temperatures used for growing rasp- 

 berries. Second, predatory mites are now available that feed 

 on phytophagous mites, and these can keep populations of 

 damaging mites at low levels. 



Compared to field production, greenhouse-pro- 

 duced berries are larger, firmer, and much less prone to fnut 

 rot. Fruit tends to be slightly less sweet and more acid in the 

 greenhouse, but well within the limits of acceptability. Vari- 

 eties differ in performance and flavor, and what might do 

 well in tlie field will not necessarily perform well in the green- 

 house. According to our research and work done in Bel- 

 gium, the variety Tulamecn from British Columbia is the 

 best floricane-fruiting raspberry in the greenhouse, although 

 it will not survive most winters outdoors in northern climates. 

 If temperatures drop from above freezing to below 10°F, 

 canes can be damaged. 



Production Basics 



Tulameen tissue-cultured raspberry plugs are planted into 

 2-gallon pots filled with equal parts sand, peat, perlite, and 

 vermiculite in May and allowed to grow outdoors on a gravel 

 bed with irrigation. While outdoors, plants are fertilized while 

 irrigating with a complete soluble fertilizer solution con- 

 taining 100 ppm N, and pest outbreaks are managed using 

 conventional practices. Rows of pots need to spaced about 

 8 ft. apart so that sufficient light will be intercepted by the 

 lower leaves on the canes. If the plants are too close to- 

 gether, the lower buds will not produce fruiting laterals once 

 they are moved into the greenhouse. In October after leaf 

 drop, pots are moved closer together and bales of straw are 

 placed around the group of pots to help protect them from 

 cold temperatures. Root systems are more sensitive to cold 

 temperatures than canes, so temperatures near zero for an 

 extended period of time will kill roots in pots that are set- 

 ting on top of the ground. In late December, plants are moved 

 into the greenhouse. (Plants may have to be moved earlier 

 if late December temperatures are forecast to fall below lOF. 

 In this case, move plants into an unheated greenhouse until 

 the end of December.) 



Once in a warm greenhouse, canes are spaced pot-to- 

 pot with 5.5 ft. between rows, trellised, and watered with a 

 100 ppm N complete fertilizer solution. Short or broken 

 canes are removed. Household fans are used to circulate air 

 down the rows to reduce pockets of high humidity (ideal is 

 65 - 75%) and the subsequent risk of fungal infection. Tem- 

 peratures are maintained at 65 - 70"F during the day, and 50 

 - 55°F at night - ideal for raspberries but too cold for most 

 other plants. Supplemental light can accelerate develop- 

 ment by 2 to 3 weeks and increase yield by 20 - 30%, but 

 may not be economical, depending on markets. 



Six weeks after moving plants into a lighted greenhouse, 

 they flower. Bumblebees are used to pollinate the flowers, 

 and fruiting can begin as early as mid-February, about 10 

 weeks after moving plants indoors. Once flowering begins, 

 the nutrient solution is reduced to 50 ppm nitrogen. With 

 one-year-old plants, double rows (with row centers 5.5 ft. 

 apart) and a pot-to-pot spacing are used so that approx. 20 

 plants are contained m each 10 ft. length of row. Each "baby" 

 plant produces about two half-pints of fruit. All but four 

 new canes (primocanes) are removed. These four will bear 

 next year's crop. 



After the first harvest is over (in April, May or June), 

 plants are transplanted into 5 or 7 gallon pots (less sand is 

 needed when transplanting into larger pots) with primocanes 



20 



Fruit Notes, Volume 65, 2000 



