This hen's egg-sized fruit is covered with a brown, fuzzy skin and has a melting green and very tasty pulp. Fuzzy kiwi, which we can purchase readily from our grocery stores, cannot be grown in Pennsylvania because of its cold tenderness and long growing season. A relative of this kiwi, though, the hardy kiwi (belonging to the species Actinidia arguta and Actinidia kolomikta) is much more cold hardy than the plant of the commercially available fruit. Hardy kiwi is of interest due to its flavor, relatively smooth (and edible) skin, "out of hand" eating size (about the size of a large grape), and its good shelf life. Commercial plantings have been established in several locations in Pennsylvania, but success does require a commitment to learning the nuances of growing the crop. Hardy kiwis have some horticultural traits that must be understood:
- Male and female flowers are born on different plants, so both males and females must be planted in roughly a 1:6 ratio of males to females.
- The plants often take several years to mature and usually do not bear fruit until they are 5 to 9 years old.
- Although the plants are extremely winter hardy--tolerating temperatures as low as -30°F--they develop shoots early in the spring that are extremely sensitive to frost. In most years, we see some shoot "burning" due to frost, although the plant usually survives, regrows, and fruits despite some spring shoot removal. If flowers are frosted, fruit will not develop that year.
- Hardy kiwi are extremely vigorously growing vines that require a substantial supporting trellis.
Despite the challenges, once one has sampled the fruit, kiwi growing gains appeal. The fruit is aromatic with fuzzy kiwi, banana, strawberry, mint, and pear flavors contained in the fruit of various varieties.
Hardy kiwi variety development is in its infancy because of the newness of this crop; however, a couple of varieties are available and can be obtained from nurseries.
This name is the common name for kiwi of the species Actinidia kolomikta, rather than being a true variety. This species of kiwi has been difficult to establish in several locations.
The name of this variety in Russian means "pineapple like." Because of the tongue-twisting name, many nursery catalogs will refer to this variety as "Anna." The fruit is of very good quality, with a sweet aroma and intense flavor. The skin is green and develops a purple-red blush in the sun. A very vigorous vine, this variety is currently the only "standard" that we have to compare to others.
Named after the public garden in which an old vine of this variety was growing and from which plants of this variety were originally propagated. Has good flavor.
Several Geneva selections are available through nurseries. Even though they are not widely tested, it is known that the fruit ripens earlier than either Anna or Issai, and that it has a good flavor.
The only self-fertile variety (not requiring a male pollinator). This variety has not performed well in Pennsylvania. It is from Japan and is less vigorous than other hardy kiwi varieties, with small fruit and good flavor. Harvesting it is a challenge because the fruit ripens unevenly within a cluster.
Available as both a male and a female. Make sure to order the female if you want fruit from it. The fruit is medium sized.
Planting and Establishment
Vines are usually purchased from nurseries as rooted cuttings or as potted plants. Order male plants that flower at the same time as your female varieties.
Dormant rooted cuttings should be planted 10 feet apart as soon as the soil can be worked in the spring. The planting row width, if rows are used, will depend on the type of trellis and the equipment used in the planting. Containerized plants may be planted in the spring after the danger of frost has passed. Distribute male plants throughout the planting. When planting, you may need to trim the roots. Plant vines just deeply enough to cover the roots well with soil, and water well. Irrigate throughout the season as needed, and monitor for insect and disease pests.
Because hardy kiwi roots burn rather easily, apply fertilizer cautiously. No fertilizer will be necessary in the year of planting. In the spring of the second year, apply 2 ounces of 10-10-10 per plant, and increase this amount by 2 ounces each year until plants receive a total of 8 ounces per plant.
Pruning and Training
In order to manage the high level of vigor of the hardy kiwi vine, plants must be pruned and trained.
Like most perennial fruit plants, they require dormant pruning; however, they also need to be pruned several times during the summer by cutting back the terminal growth to four to six leaves beyond the last flower. Also remove watersprouts (vigorous shoots originating from older wood) and shoots from the trunk, as well as vines that become entangled. This removal may be substantial during the summer.
Dormant pruning should be done sometime from December to March in Pennsylvania. On this species, flowers develop on current-season shoots that come from 1-year-old canes (last year's growth); shoots from older wood rarely produce flowers. As with grapes, a large percentage of the wood--as much as 70 percent--will be removed. New fruiting canes will have developed at the base of last year's growth (Figure 12.1). Replacement canes are left for future fruiting, and fruiting canes should be spaced between 8 and 12 inches on the cordons (permanent horizontal branches).
Figure 12.1. A fruiting branch of hardy kiwi. (To simplify the figure, leaves are not show.) Fruit are produced on shoots growing from last year's growth. Winter pruning cuts are show by //. (Courtesy of Oregon State University.)
Training should begin in the first year of planting. Like grapes, these flexible vines can be trained to a number of forms; although in commercial plantings, a pergola (Figure 12.2) is the most common training system since it accommodates the kiwi's high level of vigor. Also, like grapes, establishing the trunks and structure of the vine early in its development will ensure fruit production for many years to come. Figure 12.3 shows a typical hardy kiwi plant training system over the first 2 years of its life. For additional options, see the training systems in Grapes.
Figure 12.2.Kiwi vines trained to a pergola (T-bar) trellis. (Courtesy of Oregon State University.)
Figure 12.3 The First two years of training a kiwi vine (courtesy of Oregon State University)
- Prune to two buds at planting.
- Train one shoot as trunk, remove all others (growing season, year 1).
- Head back trunk as shoot growth at terminal loses vigor (growing season, year 1).
- Continue to remove lateral shoots, let trunk grow beyond wire, then head to just below top wire (growing season, year 1).
- Choose two shoots to form cordons (lateral trunks). Head back to 1/4 inch diameter in dormant season (growing season, year 1).
- Shoot growth, year 2. Pruning cuts in dormant season of year 2 also are shown by
Harvest and Postharvest Care
A single mature hardy kiwi plant will can yield between 50 and 100 pounds of fruit, though 50 pounds is closer to the average.
Hardy kiwi can be allowed to "vine ripen," at which time they will have about 18 to 25 percent sugar. At this time, a single harvest, rather than a selective one over several pickings, is acceptable. Unlike the other small fruits, hardy kiwi will "after ripen." Specifically, they can be harvested at a less-than-optimal ripeness (about 8 to 9 percent sugar) and then placed in storage to ripen. When picked in this manner and refrigerated, hardy kiwi will keep in a cooler for up to 2 months.
Diseases and Pests
The hardy kiwi is a relatively new crop to our area. Little information is available on the disease and insect pests that affect this crop.
Disease organisms known to infect the hardy kiwi are phytophthora crown and root rot, botrytis rot, and sclerotinia blight. Phytophthora crown and root rot is reported to be one of the most serious diseases of this fruit. The symptoms, disease cycle, and control practices for this disease are described throughout this book in the chapters on various other crops.
Hardy kiwi plants also are damaged by root knot nematodes. Insect problems include two-spotted spider mites, leaf rollers, thrips, and Japanese beetles. To control these pests, refer to the control measures listed in the chapters covering other fruit crops. As with every other crop, only compounds registered for use on hardy kiwi can be used for pest control.