Imagine growing and ripening grapes in a small pot on your windowsill. Research by two Purdue University horticulturists, Henry A. Robitaille and Jules Janick, has shown that it's possible, and in fact you can try it now with some hope of success.
In 1977, Robitaille, professor of plant physiology/fruit, and Janick, professor of genetics and plant breeding/fruit, took softwood grape cuttings with very young, developing fruit clusters and rooted them under mist. Their work showed that the fruit would continue to grow and ripen.
In 1978 they did more extensive experiments to find the best time for taking cuttings to assure fruit retention. Results indicated that June 21 (at West Lafayette, Indiana) was the best date to take softwood grape cuttings from field. At that time fruit clusters were already set and did not interfere with rooting under mist in the greenhouse.
The cuttings rooted in two weeks, after which they were transplanted to six-inch pots. Here the plants developed and, within eight weeks, produced a full-size cluster of grapes on a small pot plant. Mature clusters had excellent keeping quality and eventually produced very palatable raisins.
Robitaille says fruited grapevines growing in pots have a real potential as a fall ornamental florist plant. It is also conceivable, he says, that rooting of cuttings containing young fruits may one day allow grapes to be produced as annuals under garden conditions or in controlled environments.
This summer Robitaille and Janick plan to carry the research a step further to see if they can slow the development of the grape clusters and which varieties, both red and white, make the best potted plants. They would like to control development to bring them to maturity just before Thanksgiving.
The aim of rooting under mist is to maintain high humidity. The mist evaporates from the leaf surface of cuttings, raising the relative humidity of the surrounding air, which reduces transpiration.
Polyethylene bags also maintain high humidity. The potted cuttings are given a thorough watering and then enclosed in the plastic bag, which is sealed. Perhaps the bags may not quite do the job - it will cost very little to try it and find out.
Grapes differ from most fruits: They don't mature and improve after harvest. They must develop all their sugar and fine flavor on the vine. The best way to see if they're fully ripe is to pick a few and taste them for sweetness.
Concord, the most widely planted grape in the East, is fine for home or commercial production. It has a genetic weakness for uneven ripening when grown in warm climates such as the tidewater areas of eastern Virginia. Fredonia is an excellent early blue grape, better than Concord for warm areas because it ripens evenly and has fine flavor.