Marvin Pritts, left, professor of fruit and vegetable science, explains to visitors, including local chefs, the techniques of growing raspberry plants indoors at Cornell's Kenneth Post greenhouses last month. Charles Harrington/University Photography
Greenhouse-grown, winter raspberries have been but a dream in the Northeast. But, thanks to the efforts of Cornell scientists and their students, that dream could become next year's torte.
What started as a casual screening of raspberry varieties in the greenhouse has grown into a graduate student class project and may soon blossom into a large-scale, full-fledged agricultural industry for New York: fresh, sweet raspberries in winter.
"A lot of greenhouses sit empty up here between December and April," said Marvin Pritts, Cornell professor of fruit and vegetable science. "Once the poinsettias are gone, the growers have empty greenhouses through April. Until they're ready with their bedding plants, raspberries may be a great crop for these growers."
With greenhouse space contributed by Robert W. Langhans, Cornell professor of floriculture and ornamental horticulture, Thomas H. Whitlow's woody-plant physiology class set out to learn how western-United States varieties respond to the low-light conditions of winter in upstate New York.
"Teaching woody plant physiology in the middle of winter in Ithaca is challenging," said Whitlow, assistant professor of floriculture and ornamental horticulture. "We were looking for a crop to manipulate at full-scale indoors, to study photosynthesis and canopy architecture. As a teacher, raspberries suited my needs perfectly."
The researchers studied several varieties under these wintry conditions, including Chiliwack, Tulameen, Titan and Jewel. They studied another variety known as NY7, which has not been given a formal name.
The greenhouse results were impressive. Titans weighed in at 8 grams a berry, while Jewel weighed in at 6 grams each -- sizes approaching those of strawberries.
Lighting was an important consideration, since the growing season starts near the winter solstice, when sunshine is less plentiful. The researchers used off-peak supplemental lighting between 10 p.m. and 6 a.m. to spur the raspberries' growth.
Even more important than lighting: pollination. Moving pollen from the anthers to stigma proves tedious and nearly impossible, so the researchers brought in domesticated bumble bees.
"They pollinate better than honeybees or hand pollination," Pritts said. "Now we use them exclusively. Bumblebees are not aggressive, and we have never been stung by them -- that's in contrast to the honeybees!" Bumblebee hives are short-lived, he said, lasting only about six to eight weeks. The researchers have to replace them regularly. Bumblebee hives can be obtained from numerous vendors who import them from Holland or Canada.
Insect pests are another problem. "One advantage of greenhouse production is the absence of weeds. However, the controlled climate is ideal for other arthropod and fungal pests, if they are introduced," Pritts said. During this research, the students and faculty did not find it necessary to use any form of pesticide, and they used biological controls exclusively.
Fruiting began in late February and by late March, the harvest season was in full swing. Whitlow and Pritts invited local restaurateurs and Cornell Hotel School staff to a blind-tasting, March 21, where they compared greenhouse raspberries with offerings from a local supermarket. Opinions were favorable.
"Now that we can see that it works, we can now compete for grants and study this on an even larger scale," Whitlow said. It also could make an excellent doctoral dissertation for a graduate student. "It's a Ferrari ready to drive," he said.