Hardy kiwifruits are grape-size, borne in clusters and can be eaten just like grapes, skin and all. They have the same sparkling green flesh and a taste similar to supermarket kiwifruits, except hardy kiwifruits are much sweeter and more flavorful, and much more cold-hardy — down to minus 25 degrees.
In the humid mountain forests of eastern Asia, where the plants are native, people have been eating kiwifruits for centuries. The twining vines, both males and females, clamber up trees and sprawl over the ground; a single male is capable of pollinating the fruit of up to eight nearby females.
The two main hardy species of kiwifruits, Actinidia arguta (hardy) and A. kolomikta (super-hardy), are both grown in North America, primarily for their ability to drape arbors and pergolas with their extremely handsome foliage. Leaves of A. arguta look similar to those of apple trees, except they remain a vibrant green all summer and are attached to stems that grow on decorative red stalks.
Leaves of male A. kolomikta vines and, to a lesser extent, females, have silvery-white and pink variegations so distinctive that they look as if an artist painted them. The cup-shaped, pale golden flowers of either species are attractive, but usually they remain hidden and unappreciated beneath the foliage.
The popularity of hardy kiwifruit for eating has soared so rapidly, they have yet to receive a widely acknowledged common name of their own. As an ornamental, some nurseries sell the plant as "bower vine," so perhaps "bowerberry" is an appropriate name. "Kuwi" has been suggested, a name that combines the common and botanical names. A. kolomikta also is marketed as "Arctic Beauty" kiwifruit or grape kiwi. "Peewee kiwi" and "Piwifruit" are other possibilities. A. kolomikta fruits are smaller and ripen earlier than those of A. arguta, and they sometimes drop when ripe. A. kolomikta plants also are less rampant.
A number of varieties of both species are available. Among the A. arguta cultivars is "Anna," a Russian selection whose full name is "Ananasnaja." It's very reliable, although it just barely ripens in northern areas, including my Zone-5 New York garden. "Issai," from Japan, ripens similarly late and is somewhat self-fertile but not very cold-hardy.
Very tasty and earlier (about three weeks earlier) ripening varieties include "Geneva," "MSU" (Michigan State University) and "Dumbarton Oaks." All three were propagated from old ornamental vines in the United States. Among the A. kolomikta kiwifruits on the market are such varieties as "September Sun" and "Krupnopladnaya," which translates as "large fruit.'
Beauty and flavor come at only a small price. These plants need some care, but don't require the pesticide sprays demanded by many common fruits. Abundant sunlight (the more the better) ensures best annual production. Give A. kolomikta, especially males (whose variegated foliage scorches in full sunlight) a bit of shade in climates where sunlight is very intense. The soil must be well drained; if not, plant the vines on broad, raised mounds.
Training and Pruning
Plants look and yield best if trained to some sort of support that is sturdy and that allows the vines adequate room to ramble. I train my vines on a trellis like commercial kiwifruit growers use, which consists of five parallel wires stretched along the top of 6-by-5-foot T-bar supports spaced 15 to 20 feet apart. At some sacrifice to fruit production, but with perhaps a gain in beauty, the vigorous vines can be coaxed up a variety of other structures such as gazebos, pergolas or even along split rail fences.
Hardy kiwifruits are a bit cold tender their first two or three years in the ground. I've wrapped my young plants with corn stalks, burlap, pipe insulation and tree wrap material to shade their developing trunks and abate the fierceness of winter cold. Remember, in the wild the trunks of hardy kiwifruit are rarely exposed to full sunlight.
The goals in training and pruning kiwifruit vines are to make a potentially tangled mass of rampant shoots manageable and easy to harvest, and to keep stems bathed in enough light to remain fruitful. Pruning also stimulates new growth, which is important because fruits are borne only toward the bases of new shoots that grow from 1-year-old canes (similar to grapes).
An established vine consists of a trunk, permanent cordons (branches) and fruiting arms. First, develop the trunk by training a vigorous shoot against a 1- to 2-inch-diameter pole, tying the vine at intervals.
When the trunk reaches just above the center wire of the trellis — during either the growing season or the dormant season — develop two permanent cordons by cutting the trunk to just below the height of the middle wire and training the two shoots that grow from the topmost buds on the severed trunk along the middle wire in opposite directions. The first dormant season after the cordons have formed, cut off all excess growth along the trunk and shorten the cordons to about 2 feet.
Shorten the cordons each dormant season, leaving 2 feet of the previous season's growth, until they reach their allotted length of about 7 feet in each direction along the wires. After that, cut back the cordons each dormant season to a length of 7 feet.
Fruiting arms will grow out perpendicular to and drape over the wires. The arms should be spaced a foot apart on opposite sides of the cordon; prune away any excess arms during the dormant season. Tie the arms to the side wires to keep them from blowing around, unless they are too stiff to be brought to the wire. The first crop will form on shoots directly from these arms; future crops will form on shoots from laterals, then sublaterals growing off these arms.
After training is complete, annual pruning consists of shortening cordons each winter, as described above, and then maintaining a supply of fruiting arms. Cut laterals on fruiting arms to about 18 inches long. When a fruiting arm with its lateral, sublateral and sub-sublateral shoots is 2 or 3 years old, cut it away to make room for a new fruiting arm.
Summer pruning keeps the vines in bounds, maintains order and lets the shoots bask in light. Repeat summer pruning as needed through the growing season, and pay special attention to the vine during the critical, early days of the growing season each year. Keep trunks clear of shoots, cut back excessively rampant shoots to short stubs and cut away tangled shoots. Male plants are needed only for their flowers, so severely prune them right after they bloom: Remove about 70 percent of the previous year's growth.
Hardy kiwifruits need annual pruning for maximum fruit production, but vines will fruit with yearly, undisciplined whacking aimed at keeping them in bounds. That was all the pruning imposed on those hardy kiwifruits planted as ornamentals that you still find growing on old estates. These vines happily and haphazardly clothe pergolas with their small, green fruits hanging — not easily accessible nor in prodigious quantity — beneath the leaves.
A harvest of 100 or more pounds of fruit is possible from a single hardy kiwifruit plant, and harvests of more than 200 pounds from a mature vine are not uncommon. Harvest the fruit slightly underripe for storage: Clip off whole clusters just as their first fruits ripen. Not all fruits on a plant, even in a single bunch, ripen together, so it's best to sample a few fruits for maturity. Picked soft, with their stems attached, hardy kiwifruits keep for a couple of weeks; firm, they'll keep six weeks or more, slowly ripening to a tasty stage.
Uses of these plants need not end with the fruit. What to do with all those prunings? The leaves reputedly are good food for pigs, and the stalks are rich in a glue that leaches out with water, leaving fibers that can then be made into paper.
The plants also have an effect on cats similar to catnip, and the most novel use in this regard is in Chinese zoos, where zookeepers use an infusion of the leaves to sedate "large cats."
For more information, see Uncommon Fruits.