Must be well drained. Kiwi tree vines planted where water sits on the surface following rains are likely to develop crown rot. Soil pH should be between 5.0 and 6.5.
Related: Understanding Soil pH
The kiwi tree is especially touchy about less than perfect site and soil conditions in its youth. For this reason, some growers coddle their plants in containers for one, even two, years. Kiwi tree growth can be phenomenal in carefully watered and fertilized containers, and the kiwi tree can be protected their first couple of winters in an unheated basement or a slightly heated garage.
When setting plants in the ground in soil that doesn't drain perfectly, plant each vine atop a raised mound of earth. Winter cold bites hard at plants of all species their first two or three years in the ground, especially in conjunction with intense sunlight. A wrapping of corn stalks, burlap, or similar materials will shade the developing trunks and abate the fierceness of the cold. Delay protecting the trunks until frost has penetrated the ground an inch; the plants must be exposed to some cold in order to properly acclimate to the cold months ahead. Where winters are brutal, either due to very low or fluctuating temperatures, this wrapping may be advisable even for mature plants. Remember, trunks of wild kiwi trees growing in their native Asian forests never are exposed to full sun.
Allow 200 square feet per kiwi tree, a bit less for super-hardy A. kolomikta.
The burden of pollination rests mostly with honeybees, though wind and other beneficial insects also play a role. With few exceptions, a separate, nonfruiting male plant is needed to fertilize (and induce fruiting) of female plants. The male should be no further than 35 feet from females. Do not be surprised if it appears that female flowers have stamens, the male flower parts. The stamens are there, but the pollen they shed is sterile. Similarly, male flowers have small, nonfunctional ovaries.
Related: A Guide To Beneficial Insects
One male plant can fertilize the flowers of 8 or so females, and male and female plants need not be the same species of kiwi tree in order to cross-pollinate. Bloom times of male and female flowers must coincide, though.
Hand pollination is practical if you grow only a few kiwi trees. Merely pluck off a male blossom and lightly rub it on a half-dozen female flowers. Then go pluck another male, repeat the rubbing, and so forth.
Kiwi trees are rampant plants and their trunks never become sturdy enough to hold the plants up off the ground of their own accord. Under cultivation plants must be trained to some sort of support that is both sturdy and allows vines adequate room to ramble.
A trellis used by commercial kiwi tree growers consists of wires stretched between 6-foot-high T-bar supports spaced 15 to 20 feet apart. At some sacrifice to fruit production, but with perhaps a gain in beauty, kiwi tree vines can be coaxed up a variety of other structures such as a gazebo, a pergola, or even along a split rail fence
Training + Pruning
The goals in training and pruning are to make a potentially tangled mass of rampant shoots manageable and easy to harvest, and to keep a vine fruitful by allowing adequate light to fall within the plant canopy. Pruning also stimulates an annual flush of new wood, important because flowers, and, hence, fruits, are borne toward the bases of current seasons' shoots that grow from canes that grew the previous year only.
Related: A Guide To Vines
Not all the new shoots that grow from the previous year's canes will fruit. Some canes may have been too shaded the year before, or the vine may be too young. Those canes that are fruitful will produce fruiting shoots at their basal half-dozen or so buds; the buds further out are capable of producing shoots that will fruit the next year.
An established kiwi tree vine consists of a trunk, permanent cordons, and fruiting arms (or canes). Training and pruning are effected by tying shoots to supports and by pruning the plants while they are growing during the summer, and again while they are dormant. Late winter, before the buds swell, is the optimal time for dormant pruning.
First develop the trunk by training a vigorous shoot up along a 1 to 2 inch pole. Train the trunk-to-be against, not around, the pole, tying it at periodic intervals. If the plant has been grafted, it is important that the developing trunk originates above the graft.
When the "trunk" reaches just above the center wire of the trellis—either during the growing season or the dormant season—it is time to develop two permanent cordons. Cut the trunk to just below the height of the middle wire and train the two shoots that grow from the topmost buds on the trunk along the middle wire, in opposite directions.
Sometimes a developing trunk will make weak growth its first season, not even reaching the height of the wire. In this case, cut the trunk back by half while the plant is dormant. This will stimulate vigorous growth the following season.
The first dormant season after the cordons form, cut off all excess growth along trunks and shorten the cordons to about 2 feet. Shorten cordons each dormant season, leaving 2 feet of growth of the previous season, until they reach their allotted length of about 7 feet in either direction along the wires. After that, cut back the cordons each dormant season to 7 feet.
Fruiting arms will grow out perpendicular to, and be draped over, the wires. The arms should be spaced a foot apart on opposite sides of the cordon; prune away any excess canes during the dormant season. Tie the fruiting arms to the side wires to keep them from blowing around, unless the arms are too stiff to bring to the wire. The first crop will form on shoots directly from these arms; future crops will form on shoots from laterals off these arms.
Training is now complete, and annual pruning will consist, first, in shortening the ends of the cordons each winter to where they grew from the previous year. The fruiting arms give rise to laterals that fruit at their bases, and during each dormant season, cut these laterals to a few buds beyond where they fruited 18 inches long is about right for each lateral (or, if you want to be more precise, four buds for A. deliciosa and eight for small-fruited species). These buds likewise grow into shoots that fruit at their bases in the subsequent season; in winter, these shoots correspondingly are pruned to a few buds beyond where they fruited, and thinned to remove those that are crossing or spindly. Usually only one strong fruiting cane, whether it is the original arm or one of its laterals or sublaterals, is retained following winter pruning. When a fruiting arm with its lateral, sublateral, and subsublateral is two or three years old, cut it away to make the room for a new fruiting arm.
Summer pruning of kiwi trees is aimed at keeping the lusty vines in bounds. The trunks must be kept clear of shoots, so any that form are cut away as soon as noticed. Also, cut back excessively rampant shoots growing off the cordons to short stubs, which leaves buds for future replacement arms. Any tangled shoots should be cut away before the vine starts to strangle itself. One other bit of summer pruning: shorten fruiting arms and their laterals if they get too long.
Since male plants are needed only for their bloom, they can be pruned sharply right after they bloom, removing about 70 percent of the previous year's growth. Cut back their flowering shoots to a new shoot, which will flower the following year. Male vines do not need to put any energy into fruit production, so generally are more vigorous than female vines.
For a punctilious approach to plants on pergolas, allow the plants to grow a few, rather than just two, permanent cordons. Shorten fruiting arms to just a few buds. This drastic pruning of each arm limits the number of fruits per arm, but this reduction is compensated for by the increased number of arms on each plant because of the increased number of cordons.
All kiwi trees need annual pruning for maximum fruit production. That said, let it be known that the vines do fruit with no more pruning than a yearly, undisciplined whacking away aimed at keeping the vines in bounds. Such was the objective in pruning hardy kiwifruits planted as ornamentals at old estates. These vines happily and haphazardly clothe pergolas with their small, green fruits hanging—not always easily accessible nor in prodigious quantity—beneath the leaves.
Girdling is a technique that induces fruiting and hastens maturity and budbreak (uh-oh!) by disrupting the flow of nutrients and hormones in the stems. In late summer, make two parallel cuts, one sixteenth of an inch apart, on the trunk, and remove the strip of bark from between the cuts. Do not girdle any vine that is in a weakened condition, or cut too deeply—remove just the outer bark.
A mature kiwifruit vine can produce more than 200 pounds of fruit. One hundred or more pounds is possible from a single cold-hardy kiwifruit plant. Even in frigid, northern areas of Russia, vines will produce 20 pounds or more of this winter fruit.
Harvest semi-tropical kiwifruits by snapping them off their stalks when the skins turn brown and samples of cut fruit show black seeds. The fruit will be hard, but will soften and sweeten in a week at room temperature. In a cool room, such fruit will keep for two months. If the fruit is refrigerated to near freezing, and the humidity maintained at 95 percent (with a plastic bag having just a few small holes, for example), the fruit will store for 9 months! Let firm-ripe fruit soften before eating. This can be hastened by putting the fruit in a bag with an apple.
Hardy and super-hardy kiwifruits drop or come off easily from the vines when they are ripe. Picked firm-ripe with their stems attached, these small fruited kiwifruits store as well as the large kiwifruit.
Excerpted from Dr. Lee Reich's Uncommon Fruits Worthy of Attention