Kiwifruit, which has replaced the old English name of 'Chinese gooseberry', are native to the mountains and hills of southwestern China where they grow wild in trees and on bushes. The kiwifruit was introduced to the United Kingdom, Europe, United States, and New Zealand between 1900 to 1910 from China. Commercial plantings were made in New Zealand about 1930 and have become widespread over the last 20-30 years.
There are over 50 species in the genus Actinidia to which the kiwifruit belong. All of these are long-lived perennial vines or creeping types. The plants are dioecious which means that male and female flowers are found on different plants. Thus, one male plant is needed for each eight female plants for pollination. Male plants do not produce fruit. Fruit range from round to oblong in shape and from smooth-skinned to hairy. Flesh color may be green, orange, or yellow.
'Hayward' is a female variety of A. deliciosa var. deliciosa that is now the primary variety grown commercially. This is because of its large fruit size, superior keeping quality (up to 6 months) and fine flavor. There are now a number of strains of 'Hayward' being grown.
'Hayward' fruit are fuzzy, brown and oblong in shape. The flesh is tart-sweet and tastes like a combination of citrus, melon, and strawberry. When fruit are cut crosswise the emerald-green flesh has a ring of small black edible seeds. This variety is primarily grown in California's Central Valley in the United States. It is only winter hardy down to approximately 10 degrees F and consequently will not survive in the mid west.
A. arguta is more cold hardy than the kiwifruit and is reported to survive temperatures of -25 degrees F. This is the species that has been purchased and planted by many backyard fruit growers in the midwest. Fruit size is considerably smaller than that of 'Hayward' and is about the size of a large sweet cherry. The skin of A. arguta is smooth and consumed with the fruit. Fruit are greenish-yellow in color and acidic until ripe. When ripe they are very sweet and juicy and the flavor is considered to be better than that of the kiwifruit.
A. kolomikta has smaller fruit than A. arguta. A. kolomikta is very winter hardy and will survive temperatures down to -30 degrees F. Fruit are very sweet and have a superb aroma and flavor. They are also very high in vitamin C which can be one percent of the fresh weight. The vine is the least vigorous of the three Actinidias discussed here. It is generally known as a landscape plant for its pink and white variegated leaves which are particularly attractive on the male plants.
Both A. arguta and A. kolomikta are called hardy kiwi and have not succeeded in commercial plantings thus far. They are primarily grown by amateur horticulturists in areas where midwinter temperatures prevent the growth of kiwifruit.
One of the primary problems in growing any of the Actinidia species is that the plants begin growing early in the spring and the young shoots and developing flower buds are extremely susceptible to injury from spring frosts. They can be damaged by even brief exposures to 30 degrees F or lower. Thus, the flower buds are normally killed by spring freezes and the plants rarely produce fruit. Successful cropping of kiwifruit may require a long frost-free growing season of about 220 days.
The plants, particularly young plants, are susceptible to trunk injury from spring frosts. The trunk increases in hardiness as it gets older and develops a thicker layer of bark, but it is recommended that the trunks be protected. This has been done by laying the plants on the ground and covering them with leaves, wrapping the trunks or using sprinklers and heaters for frost protection.
Hardy kiwi often do not survive the first growing season. This is generally due to planting in a poorly drained soil and the development of root rot or neglect after transplanting.
Survival can be improved by growing them in a five gallon container for the first season. Plants should be staked and transplanted only after they have become well established late in the first growing season or after the danger of frost is past the following season. The plant must be transplanted to the yard or the container must be protected during the winter to prevent the roots from freezing. Water the plants adequately, but not excessively.
Select a planting site that has good air drainage, and one that is protected from high winds and is not frost prone. The soil should be a well-drained loam, since heavy clay soils make plants much more prone to root rot. Plants do best when the soil pH is around 6.5. Set plants 15-18 feet apart in the row.
Fertilization involves mixing one pound of organic fertilizer or 2 to 4 oz of a slow release fertilizer with the soil at planting. The roots are very sensitive to fertilizer burn, so over fertilization should be avoided. At the end of the growing season apply one-half pound of 10-10-10. In subsequent years fertilize twice a year, once in early spring when the plants are dormant and then just after bloom in early June. Apply 1 lb of 10-10-10 in the spring and 0.75 lb after bloom the second year and 2 lbs. in the spring and 1 lb. after bloom the third and future years. Distribute the fertilizer well over the entire root system to avoid root injury.
There are several different trellis types and training systems available. The T-bar trellis will be described here. Construct your trellis prior to or shortly after planting. It must by strong enough to support the weight of the plants. Use posts that are from four to six inches in diameter and eight to nine feet long. Locate a post at each plant (15-18 ft apart) and set them two to three feet deep. Brace the end posts well. Attach a five-foot long two-by-four cross-arm to the top of each post and brace it back to the post with wire or wood. Then stretch three 8 to 12 gage wires along the tops of the cross-arms. Place two of the wires at the ends of the cross-arms and one down the center.
Train a single shoot up each post to the top of the trellis by removing any lateral growth. Tie the shoot, which will form the trunk loosely to the post and prevent it from winding around the post.
At the top of the trellis, train the shoot along the center wire in one direction. The following year a shoot will be trained along the center wire in the opposite direction. These two shoots will form the permanent leaders on the vine. Prevent these leaders from twisting around the center wire, since this can weaken the vine in future years. The lateral canes that develop from these leaders are tied perpendicular to the leaders to the outer wires. These canes will be the fruiting canes the following year.
The main leaders that were trained to the center T-bar wire are permanent unless they become weak or winter injured. Then they are renewed by tying down a new vigorous shoot. Replace all other wood on an annual cycle in late February. Pruning should be done well before growth starts in the spring to prevent vine bleeding. Remove most of the wood that fruited the previous year and any twisted or broken canes. Retain vigorous one-year-old canes that have not fruited and are well spaced (about every 10-15 inches) along the leaders and form a single canopy layer. Prune these back to the first eight buds. Where vigorous one-year-old canes have not developed or vegetative vigor is reduced, retain the fruiting arms that fruited the previous year by cutting back to eight buds past the last fruit bearing leaf axil. A small percentage of spurs are also retained for fruit production. These are short laterals that have terminated their growth back close to the leaders. They are produced usually when strong shoots are cut back.
As an alternative to the single trunk training practiced in most areas where the hardy kiwi is grown, recommendations for the Eastern United States suggest the use of multiple main trunks. This is primarily due to trunk splitting and injury due to spring frosts. Multiple trunks can be developed from the ground and each trained as a leader on the trellis. If one trunk is injured, it can be removed and still leave a large proportion of the plant.
Inspect plants in the spring for trunk damage. If the bark is lifted completely around the trunk, prune the trunk off below this damage. Vigorous regrowth from the stump will replace the trunk.
Summer pruning is begun just before flowering. Remove shoots that do not have flowers that originate outside the wires. Flowering shoots are cut back four to six leaves past the last flower. Tangled shoots are also removed. Later in the summer, shoots that are not needed for replacement canes are removed and replacement canes are tipped to prevent tangling.
Since male plants do not produce fruit they can be particularly vigorous. These plants are pruned immediately after flowering and the flowering shoots are cut back to vigorous new growth closer to the leader. Male plants are not pruned during the dormant season so that maximum flowering is achieved.
Irrigation is important for a number of reasons. Lack of water will reduce fruit size, reduce flower numbers, and induce early fruit drop. Drought will also induce leaf drop and early fruit ripening which leads to uneven ripening and poor fruit flavor. Water stress also delays the development of vine maturity and appears to reduce vine fall hardiness.
Flowering on vines that have not been damaged by spring frost normally occurs on three-year-old vines. If the plants were propagated from juvenile vines instead of mature vines by the nursery, flowering may take an additional year or two to begin. Flowering takes place in late May.
The fruit quickly sizes after pollination and reaches its full size in the middle the summer. However, the remaining portion of the season is required to mature the fruit. Harvest usually takes place in late September and the fruit are picked before they are ripe. Fruit taste better when picked, refrigerated and ripened as opposed to ripened on the vine.
To determine when to pick, harvest a few fruit and allow them to soften for a few days. When fruit ripens to a suitably sweet flavor, harvest all of the fruit and refrigerate them. Fruit will store in the refrigerator for five to six weeks. Removal from the refrigerator initiates softening and ripening and should be done several days before eating. All of the hardy kiwi varieties have a similar flavor. Hardy kiwi often reach sugar levels of 20 percent and are considerably sweeter than the 'Hayward' kiwifruit. The fruit also contains large quantities of the enzyme actinidin, which will tenderize meat.
Phytophthora crown and root rot is one of the more serious diseases of hardy kiwi. It causes weak plant growth and the development of small yellow leaves. Terminal growth may be stunted or die back. Plants often collapse and die during hot weather. This disease occurs on heavy wet clay soils and these soil types should be avoided when planting. Over irrigation can also lead to Phytophthora root rot.
Hardy kiwi plants are also damaged by root knot nematodes. Two-spot spider mites can build up on plants during hot, dry weather, particularly on greenhouse grown plants and occasionally outside. Japanese beetles will do some leaf feeding.
There are several reports of cats digging up the roots and clawing the plants and foliage. Hardware-cloth or chicken wire trunk protectors are recommended for this problem.
This information was developed from information derived from the Actinida Enthusiasts Newsletter, Small Fruit Crop Management by G.J. Galletta and D.G. Himelrick, conversations with Daniel Milbocker at the Hampton Roads Agricultural Experiment Station in Virginia Beach, VA, and Michael McConkey of Edible Landscaping Nursery in Waynesboro, VA and through limited observations and experience with kiwifruit and hardy kiwi.
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