A properly trellised Hardy Kiwi showing the original stake
Immature Hardy Kiwi fruit on the vine
An improperly trellised Hardy Kiwi vine on a tree trunk
Hardy Kiwi Fruit
The hardy kiwi may be an aggressive grower, but is slow to mature and produce fruit. However, once it begins fruiting, it is extremely productive. Hardy kiwi, Actinidia arguta, is one of 90 different species of kiwi and is a close relative to camellias. It has been known by a number of different names over the years such as kiwiberry, baby kiwi, and Siberian kiwi. A. arguta is sweeter, more cold hardy, and more nutritious than its fuzzy supermarket cousin, kiwifruit or Chinese gooseberry, Actinidia deliciosa, with which most people are more familiar. Hardy Kiwi is native to Korea, Siberia, and the hills of southwest China. It wasn’t introduced into the United States, the United Kingdom, New Zealand, and Europe until the early 20th century. In 1906, seeds were taken from China to New Zealand to be planted. Commercial growers in New Zealand started planting hardy kiwi on an extensive scale in about 1930. It took New Zealand farmers giving it a name change and the marketing of produce brokers for it to become widely known in the United States. But, it is still not as popular as the hairy variety. Today, New Zealand and China are the largest producers of hardy kiwi. In the late 1960s, commercial plantings began in California. Commercial growers have also sprung up in Oregon and Pennsylvania in the last 20 to 30 years. But, growing hardy kiwi remains mainly an experiment in North America.
The hardy kiwi plant is a highly vigorous, deciduous, perennial woody vine. The vines are dioecious, meaning male and female flowers are borne on different plants so both sexes must be planted in order to produce fruit. It has 3- to 5-inch, deeply-toothed, glossy, deep-green leaves. The stems have a bright red tint. The 1- to 1 ½-inch, fragrant, white flowers have dark brown centers with purple anthers and are borne on the previous year’s growth. The 1 inch fruit are about the size of a large grape and are held in clusters. The fruit have a thin, shiny, smooth, brownish-green skin which wrinkles when ripe and emerald green flesh. The skin of the fruit is edible so peeling isn’t necessary. The fruit is aromatic with hints of pear, banana, strawberry, and pineapple flavors. The fruit’s sweet flavor and their convenient size make them an easy choice for raw eating.
Hardy Kiwis grow in zones 4 to 9 and are extremely cold hardy even down to -25 degrees Fahrenheit. However, their flower buds and young shoots can be damaged by late frosts so avoid planting them in low-lying frost pockets. Try to plant them in a northern exposure site where they will get some warmth from the sun in early spring. They perform well in partial shade and may do better with 20 to 50% shade in warmer arid climates. These plants are also susceptible to wind damage, especially in hot, dry conditions. So, construct a windbreak or plant along a building or fence that will offer some shielding from drying winds. Hardy kiwis like a loamy, well-drained soil that is rich in organic matter with a slightly acidic pH of 6.5 to 7. These plants do not tolerate poorly drained, heavy soils. Hardy kiwis require support, so give them plenty of room for their trellis system which is detailed below.
It is easier to establish your vines using containerized plants instead of bare root plants. Plant your hardy kiwi in mid to late April after any chance of frost. Dig a hole much deeper than the root ball and mix in lots of organic matter such as leaf mulch, peat moss, or ground pine bark. Plant the root ball about an inch above ground level and mound up a deep application of mulch, this will aid with drainage. Mulch heavily the first fall to protect the young roots. Water the new transplants frequently for the first 2 weeks. Hardy kiwis don’t like to be too dry, so water abundantly during the growing season, especially in arid climates.
If planting multiple plants, place them 10 feet apart. The male varieties can be planted side-by-side with a female fruiting variety if need be. Train 1 main cane of each plant on a 7 foot bamboo or fiberglass stake. Tie it loosely to the stake and monitor it closely to assure it grows straight and doesn’t curl or twist around the stake. It may take 1 to 2 years for the primary cane you have chosen to reach the top of the stake. Once the cane reaches the top of the stake, prune the tip to encourage lateral growth to form. Choose 2 lateral shots and attach them to the wires of the trellis to protect them from wind damage and offer them support.
Hardy kiwi vines require a substantial support system in place since they are incapable of supporting their own weight, especially while fruiting. Support of the vines is usually done in one of three ways: a single wire trellis, a patio cover/awning as support, or by a 3- to 5-wire T-bar trellis system. Situate your chosen trellis system so the staked plant is at the center of the system.
The T-bar system is by far the best trellis system and is what is normally used in commercial production. It can be built with two, 8 foot tall, 6 inch x 6 inch, cedar or pressure-treated wood posts each with a 5 foot, 4 inch x 4 inch cross-arm bolted in place at the apex of the main posts to form the T-shape support. Anchor the support posts 2 feet deep in concrete 10 feet apart. Also, put 2 foot dead-man post cemented underground at a 90-degree angle to each support post. Attach 3 to 5, 8- to 10-gauge, galvanized wires equal-distance apart along the cross-arms in a clothesline fashion. Use eyelet screws to attach the wires to the cross-arms. Stretch the wires tautly between the two cross-bars with a come-along. The wires should have a 300-pound tensile strength in order to support the heavy vines when fruiting.
Hardy kiwis do not like to get too dry. The vines and large leaves of the hardy kiwi transpire large amounts of water rapidly during the hot, windy days of late spring and summer. So, it is necessary to water young transplants deeply once a week. Established kiwis need a great deal of water also and should be irrigated throughout the growing season as needed for optimum plant growth and good fruit production. Overhead irrigation by sprinklers or by hand watering is acceptable, but drip irrigation is more efficient.
Hardy Kiwis burn very easily, but they are also heavy nitrogen feeders, so apply fertilizer judiciously. Don’t fertilize the first year after planting to let the young plant get established. Early spring the second year, apply 2 ounces of 10-10-10 N-P-K fertilizer per plant. Increase the application by 2 ounces each year until you are putting out 8 ounces per plant, then do not exceed this amount of fertilizer per plant in the following years. These applications can be split with half in early spring and the other half in early summer. Don’t fertilize after June in order to let the plants harden-off for winter. Instead of chemical fertilizer, well-aged manure can be applied at a rate of 3 to 5 pounds per plant in late winter and again after fruit set. To avoid crown rot, do not apply manure or mulch in direct contact with the vine.
Pruning and Training
As mentioned earlier, you must prune the tip of the primary vine once it reaches the top of its 7-foot support stake in order to promote lateral growth. Once 2 lateral branches or cordons are produced, drape them over the center wire in each direction of your trellis system. These cordons will form the permanent framework of your trellised plant. Fruiting laterals will develop about every 24 to 30 inches along these cordons and grow perpendicular across the wires of the T-bar trellis. During the first dormant season, cut these first year fruiting laterals just beyond the outer most wire of the trellis. Kiwi vines must be pruned throughout their lifetime in order to keep the plants tidy and promote maximum fruit production. They produce their fruit on current season’s growth that comes from 1-year-old wood. Thus, it is important to maximize these fruiting laterals each year. When maintained like this, the vines can stay productive for 60 years or more. It is best to do most of the pruning in late winter while the plants are dormant, this will avoid excessive bleeding of sap that is prone to happen during the growing season. Light pruning several times during the growing season to manage the rampant growth by simply nipping off any overlapping leaves or stems that might shade out fruit is acceptable, but don’t cut any vines of a quarter inch or more.
Since hardy kiwis are dioecious (male and female flowers are on separate vines), female plants produce the fruit but male plants are also needed for cross-pollination. One male plant pollinizer inter planted among five to nine females is usually enough to ensure good pollination. Because different cultivars bloom at different times, make sure that both the male and female plants bloom at the same time in order to guarantee pollination. Pollination is done by wind or insects such as honeybees.
Propagation can be accomplished by seeds, cuttings, layering, or grafting. When done by seeds, remove the seeds from a mature fruit and let them dry on a paper towel for two days. Next, refrigerate them for four months in moist perlite at 40-degrees Fahrenheit to fulfill the stratification process. Then, plant the seeds no deeper than 1/8 inch in a seedling potting soil mix. Cover the container with plastic to keep it moist and the humidity high. Uncover the container once the seedlings start to germinate. When all the seedlings are up, put a thin layer of clean sand on top of the potting medium. Also, keep the seedlings well ventilated since they are prone to damping off. Transplant the seedlings to individual 4-inch pots once they have put on 4 true leaves. After the plants get 6 inches tall shift them to a 1-gallon pot. Later, when the plants get 12 inches tall, transplant them to where they will be growing.
When propagating by cuttings, you can take softwood cuttings in late spring of wood that has had at least 500 chilling hours or ripe hardwood cuttings in October or November. Clip the cuttings just below the node and remove the 2 lowest leaves and use a rooting hormone like indole-3-butyric acid (IBA) before sticking the cuttings in a well-drained soil medium comprised of 50% peat moss and 50% perlite or a mix of equal parts garden soil, perlite, and peat moss. In order to expedite rooting, employ bottom heat and mist irrigation inside a hoop house. Also, use plastic sweat tents or cloches made from 2-liter soda bottles to keep the humidity constant. Cuttings usually take 6 to 8 weeks to root properly.
Pest & Disease
These fruit are not normally affected by most pest and disease problems. Their fruit, unlike most fruit and berries, does not attract birds. But oddly enough, cats can be a major problem with damaging the bark of young vines because of their catnip-like scent. Cats like to rub up against the vines and can cause damage to the new growth. Protect young vines from cat damage by building small chicken wire cages. Garden snails can also be a problem on younger plants. Voles, deer, and rabbits can be a problem as with so many other crops. Root knot nematodes can be a problem as well, but can be controlled with predatory nematodes. Scale insects and greenhouse thrips can be damaging, too, if allowed to reach extensive populations. But, the most prevalent problem is root and crown rot that is exacerbated by poorly drained, heavy soils like southern clay soils. Hardy kiwis have fleshy roots that are prone to root rot when they sit with water around them too long.
Harvest & Storage
The fruit ripen in late summer or early fall depending upon the variety. The harvest usually comes as one single, large, manageable harvest instead of a selection harvest over several pickings. The kiwi fruit are ripe when they become soft to the touch, are slightly wrinkled and pull off easily. They taste best when harvested completely ripe. But, can be picked early while still firm then ripened with the ethylene gas from a bruised apple or banana in a paper bag. When harvested early in this manner, they can be stored in the refrigerator using an air-tight plastic bag for up to 2 months and consumed as needed. Hardy kiwis have a shorter shelf life due to their higher sugar content (18 to 29% sugar content) that is nearly double that of their fuzzy commercial relative. Although, it may take up to 5 years before hardy kiwi start to bear fruit, they are one of the most prolific fruiting plants. A single mature plant can yield 50 to 100 pounds of fruit per year.
Hardy kiwis can be eaten fresh as a snack or added to tropical-style salads. Nutrient-packed hardy kiwi can be used as a practical ingredient to bakery goods. The fruit can be sun dried or pickled in brine as is popular in China and Japan. The juice can be made into a delightful wine. The juice can also be used as a meat tenderizer since it has the enzyme papain, which is also found in papaya. When adding the fruit to dairy or gelatin dishes, cook it first to neutralize the enzyme.
The fruit of the hardy kiwi is higher in vitamin C than oranges. One serving can have over 200% of the RDA for vitamin C. Vitamin C assists in boosting the immune system, healing wounds, as well as increasing iron absorption. Scientific studies show that dietary fiber and phytonutrients in the fruit not only inhibit some cancerous cell growth, but are cytotoxic to the malignant cancer cells without affecting normal cells. Eating this fruit has cardiovascular benefits also by reducing triglycerides in the blood, thus avoiding blood clots, and the trace mineral chromium helps regulate heartbeats. Other studies show that consuming kiwi fruit weekly aids in lessening the effects of asthma. Asthmatics experience decreased wheezing, coughing and shortness of breath during the study. Hardy kiwi is a source of lutein and zeaxanthin, two phytochemicals which contribute to eye health. The fruit’s vitamin A also protects the eye from macular degeneration and cataracts. These nutrient-rich fruit also have high levels of folate, vitamin E, vitamin K, potassium, calcium, magnesium, phosphorous, and other anti-oxidants that are helpful in neutralizing free radicals.
Development of new varieties of hardy kiwi is still in the early stages due to the newness of the crop in the United States. Several standout varieties are as follows:
‘Ananasnaja’ or ‘Anna’ – bears relatively large smooth fruit with a sweet aroma and intense flavor. Fruit color is green to a red-purple blush. The stems have a red tint. It is highly productive and recognized as the standard by which all other varieties are compared. Does best in Zones 5 to 7.
‘Geneva’—the fruit has good quality and good flavor. It ripens earlier than ‘Anna’.
‘Dumbarton Oaks’—the fruit is green and slightly ribbed. Appropriate for short-season areas since they produce early but will do well in all regions of Zones 5 to 7.
‘Issai’—is one of the few self-fruitful varieties. It has small sweet green grape-size fruit. The vines are less vigorous and produce far less than other varieties. This cultivar will have larger harvests when cross-pollinated. Good for Zones 5 to 8.
‘Langer’—shows promise since it tolerates many adverse conditions such as drought, high winds and severe cold. It yields medium-size fruit of good quality.
All varieties of hardy kiwi except ‘Issai’ and an experimental variety, ‘119-40B’ require a male pollinizer. A couple good male pollinators are ‘Male’, ’74-46’, and ‘Meader’ (male).
Other hardy kiwi cultivars of merit are ‘Ken’s Red Hardy’, ‘Fortyniner’, ‘Michigan State’, and ‘Meyer’s Cordifolia’.
References & External Links
- The Berry Grower’s Companion, B.L. Bowling, pp. 231-238, Timber Press, 2000.
- Edible Landscaping, R. Creasy, pp. 249-251, Sierra Club Books, 2010.
- Growing Kiwifruit, Oregon State University Extension, 2005, http://catalog.extension.oregon.edu/sites/catalog/file PNW 507.
- Kiwi Fruit: Health Benefits and Nutritional Value, https://www.organicfacts.net/health-benefits/fruit/kiwi.html.
- Kiwifruit Production Guide, D.G. Himelick & A. Powell, Auburn University Publication ANR-1084, 1998.
- Hardy Kiwifruit, https://www.crfg.org/pubs/ff/hardy-kiwifruit.html.
- Kiwifruit Production in California, J.A. Beutel, University of California – Davis, Small Farm Program, Division of Agriculture and Natural Resources Publication, 1990.
- Uncommon Fruits Worthy of Attention, L. Reich, pp.121-138, Addison-Wesley, 1991.