Growing Hardy Kiwiberries in the Home Garden

The hardy kiwiberry (Actinidia arguta) is a deciduous, fast-growing, woody vine grown for its attractive foliage and edible fruit. Fruits are sweet, grape-sized berries with slight differences in size, shape, taste, and time of ripening for each cultivar. Hardy kiwiberries can be grown in USDA planting zones 5a-7a and even withstand temperatures of -25°F to -30°F.  In the mid 2000's, the fruit became known worldwide as the commodity “kiwiberry." Today, commercial and small producers are growing these vines globally for their edible fruit.

Two other Actinidia species familiar to many are A. deliciosa, the fuzzy, brown, egg-shaped fruit commonly seen in grocery stores and A. chinensis, a newer, sweeter kiwi with a golden interior. Neither of these species can be grown in our Pennsylvania climate.

The hardy kiwiberry is native to Japan, Korea, northern China, and the Russian Far East. Seeds were brought to the United States from Japan in 1877 by US Colonel William S. Clark, founding president of what is now the University of Massachusetts Amherst. Over following decades, kiwiberry plants could be found in nurseries and were used in the early 1900’s by landscape architects, such as Frederick Law Olmsted, to soften the appearance of walls, buildings, and fences in their landscapes. Beatrix Farrand, designer of Dumbarton Oaks in Washington, DC, used these vines in her design of that garden. A. arguta ‘Dumbarton Oaks' is a named cultivar still available today. Hardy kiwiberries fell out of favor as an ornamental landscape plant in the 1930’s but are still available from regional nurseries.

Growing kiwiberry vines is an investment in time and a labor-intensive crop to maintain. Vines have a life expectancy of eighty plus years; they are aggressive growers.  While kiwiberries can produce fruit in their third to fifth years, vines only begin to reach their full harvest potential in their eighth to twelfth years.

Site Selection

Choose a site that is in full sun; has good air drainage, a downslope flow of relatively cold air; and is not in a frost pocket. If planting on a hill, a north-facing slope is best to decrease the risk of late spring frost damage. New flower buds and shoots emerging in the spring are sensitive to sudden temperature drops. While the vine will most likely recover, if flower buds are damaged, no fruit will form that year.

Avoid sites with consistently high winds or that experience heavy wind gusts. Strong winds can cause damage to the vines and/or flower loss at the time of pollination. Fruit rubs due to wind also can cause cosmetic damage to the fruit  Wind damage can be mitigated by planting windbreaks. Be certain to plant windbreak trees far enough away from the kiwiberry beds that their roots do not grow into the beds. Check with your tree nursery concerning the root structures of any trees you are considering for windbreaks.

Soil should be well-drained and have a pH of 6-7. Hardy kiwiberries prefer “dry feet"; heavy, wet soils promote root rot. Kiwiberry vines can be sensitive to macro- and micronutrient deficiencies. A soil test is recommended, and it is important to check for adequate organic matter and trace nutrients. Plan six months to one year before planting in order to have your beds ready. Vines are grown in rows and optimum spacing between vines is eighteen feet.

Kiwiberry vines are dioecious; a male and a female vine is necessary for pollination and fruit set. A raised bed approximately 4 feet wide is ideal. Turning the soil to a depth of 2 feet will aid in both water drainage and root development. A ratio of one male vine to four to six female vines is suggested.

Trellising and Irrigation

A major expense will be the construction of a strong support structure for the kiwiberry vines as, at maturity, each female vine can bear as much as 100-150 lbs. of fruit. Two trellis supports are commonly used, the overhead pergola and the T-bar system. The T-bar system is advantageous for the growth characteristics of the vine, ease of pruning, and allowing fruit to be accessible for harvest.

Ideally, your bed preparation will be complete and support structures installed prior to or soon after planting. At a minimum, there should be one line post with one wire 3" below the top of the stake to attach bamboo stakes and  irrigation, if using elevated irrigation system. A bamboo stake, used to train the vine, should be installed prior to planting. T-bars and the additional 5-wire system can be installed at a later date. As the goal is to have more fruit nearer the periphery of the structure, a T-bar system exposes fruit to sunlight, promoting ripening and flavor. Since the canopy of kiwiberry vines are thick and have large leaves, airflow through the vines also will mitigate fungal problems.

Newly planted vine. Photo credit: Barb Kline

Once the vines begin to grow, you will need to have supplies to attach the vines to the center T-bar wire. Using a five-wire T-bar system of twelve-gauge wire, you will need “branch loks" and rubber “tab bands." These supplies are available from an orchard/grape company.

Irrigation is important.  During dry periods with summer drought, stress can weaken the vines, especially in the first year. In subsequent years, drought also will induce leaf drop and stress the growth of the vine, reducing the number of flowers, decreasing fruit size, negatively affecting Brix (a measure of sweetness), and causing fruit drop.  Drip irrigation is a good solution and is environmentally responsible.

Vine Selection

Each kiwiberry cultivar has its own characteristics and the fruit they produce have their own color, shape, size, and unique flavor. There are only a few reputable nurseries in the United States that handle A. arguta vine stock.  Vines can be purchased as potted plants for about $30 each, depending on pot size and the age of plant. Ask the nursery staff the size of the pot being sold, how old the plant is, when it was last ‘potted up', and if it is greenhouse grown or has been hardened off outside.

After purchase, young vines should be kept in their pots in a shaded area and watered until they are planted out into raised beds.  Remove each plant from its pot and inspect the roots. The plant should be almost root bound with good thick, white, and some stronger yellow roots.

The flowering schedules of each cultivar are important as the blossoming time of a male plant should coincide with that of a particular female cultivar in order for pollination to occur. Some cultivars may not acclimate well to your specific climate/microclimate. Discuss your climate, location, and soil conditions with a reputable nursery prior to purchase to determine plants that will do well in your area.

A. arguta ‘Issai' is the only cultivar that is sold as “self-fertile." ‘Issai' will not pollinate other A. arguta species as its ploidy (chromosome structure) is different. In addition, it is not as cold hardy and fruit size, quantity, and quality are said to be inferior.

Descriptions of kiwiberry fruit flavor vary. Some describe the taste as similar to fuzzy kiwis or with hints of pineapple, black currant, ripe strawberry, pear, banana, mint, melon, and other tropical flavors.

Planting and Trellising

Prior to planting a male and female vine, insert a  7-foot bamboo support in the soil of the raised bed and secure it to the top center wire of the trellis.  Plant in spring/early summer after there is no danger of frost or in autumn before the weather turns very cold and the ground freezes. Since plant roots are sensitive and burn easily, do not fertilize at planting.

Dig a hole in the raised bed next to the bamboo stake. The hole should be 8 inches deep or more to accommodate the root ball of the vine. Loosen plant roots before planting. Soil may be hilled up around the vine base. Attach the vine to the support stake with a flexible tie to allow for growth.

During the second year, new, sturdy, green shoots will sprout from the bottom of the vine. Choose the strongest of these shoots and attach it to the bamboo stake with a flexible tie. Using a max tapener gun with flexible tape to lightly align the young vine to the stake will ensure a straight shoot.  This shoot will become the main trunk of the vine, and, if straight, will assist in holding the mature vine upright. If the vine begins to wrap around the bamboo stake, unwrap and straighten it. Continue to attach the vine to the stake as the plant grows and prune away any original woody vine growth.

Side shoots, growing on the main vine trunk should be pruned off so that the energy of the vine is directed to the main stalk. When the vine grows above the central wire, cut it back 6 to 8 inches below the central wire just above a leaf stem to break apical dominance. Two stalks will then sprout and become the left and right cordons. Forming a gentle curve, train the new cordons to lie on top of the center wire, forming a Y-shaped structure. Lightly tie these cordons to the T-bar center wire until cordon growth lengthens. These cordons are the second part of the permanent framework.  As the vine matures, extend the cordons with new annual growth until you reach the desired length, about nine feet on either side of the main stalk.  Cordons should be terminated a minimum of 1 to 1 1/2 feet from the cordon of the next vine.

Photo credit: Kiwi Berry Organics Co.

In ensuing years, laterals will grow from the cordons. They should begin to appear by year three and will take several years to fill out. The cordons will produce more laterals as they age. Train the laterals out across your wires on either side, spacing them a minimum of 12 inches apart.

Cordons and laterals will produce terminating fruit spurs where growth stops. Non-terminating fruit spurs will have green growth tassels and should be pruned back after fruit set to the second node after the last fruit so that they do not wrap into the vines. Terminating spurs coming directly off the cordon and growing in the shade will produce fruit that will ripen at a faster pace and stay green. Prune off these spurs. If left on the plant and allowed to fruit, harvested fruit from these spurs should be separated from the remainder of the harvest as it will ripen faster and shorten the shelf life of the entire harvest. Fruit harvested from terminating or non-terminating fruit spurs on the mid-to outside of the laterals will have a longer shelf life.

The laterals that produce fruit during the current season should be pruned off during winter/dormant pruning. New laterals that have grown since July will replace the old laterals that produced fruit. Laterals should be replaced every year. Vines will twine around wires, other vines, or anything they can reach. If they begin to do this, unwrap them.

In this drawing, the leaves are not included on the right side so that you can see the vine structure.  Photo credit: Kiwi Berry Organics Co.

Pruning during the first few years is easier to accomplish as the goal is to create a structure. As vines become mature, pruning will become a more labor/time-intensive task. Established vines can grow 1 inch each day during the growing season.

Maintenance/ Pruning

Remove any weeds in raised beds that would compete with vines for water and fertilizer. Kiwiberry vines are very sensitive to any type of weed suppressant sprays, such as Roundup. Use of such products can kill a vine. Weed by hand or, if using a hoe, do not work the soil too deeply as the roots of young vines are organized as a net and are usually found about 6 inches below the soil surface. At five years of age or more, vines will begin to form taproots.

Mulching vines retains soil moisture, requiring less irrigation; controls weeds; reduces spring freeze damage; and keeps soil cooler to delay bud break.

After the first year, fertilizer can be applied in the later part of April after leaf set. An application of an organic slow release 4-2-4 NPK ratio is suggested. For young vines, apply 2 ounces of fertilizer in a 6 to 12-inch circle away from and around the trunk. As vines age, gradually increase the amount up to a total of 16 ounces for vines five years and older. Spread the fertilizer horizontally in line with the vine cordons to encourage the roots to extend out from the trunk yet remain within the raised bed. Apply fertilizer just prior to a forecast of rain so that it is activated and absorbed into the soil by the rainfall. Adding a higher N fertilizer will increase vegetative growth and may change flavor of the fruit.

An open framework promotes the access of air and sun to the vines and flowers and assists in the ripening of fruit. Increased airflow also allows for increased pollination and decreased humidity and fungal diseases. If pruning is not maintained as the vines mature, pollination may not occur, or the harvest quality and quantity could be negatively affected.

In years three and four and beyond, pruning must be done almost continuously during the growing season and then once while plants are dormant to maintain vine structure. After fruit set, pruning should decrease the vigorous vegetative growth and open the canopy to the sun. Prune back large water shoots growing from the outer two-thirds of the laterals to the base of the lateral. Shoots growing straight up from the cordon and the back one-third of the laterals can be left as a ”trap" crop for Japanese beetles. These shoots will eventually get heavy and lie down on top of the existing canopy. Some of these shoots later will be used as replacement laterals during dormant/winter pruning. Prune new laterals laying on the wires 6 inches beyond the outside wire to avoid vines twining together or growing into adjacent areas.

Dormant/winter pruning is done after leaf drop in autumn/winter until prior to sap rising in the spring.  During this time, replace laterals that have produced fruit as you can see the structure without leaf cover.  Choose new laterals that are the width of a pencil and a minimum of 12 inches apart. Lay the laterals down and attach them to the wires. These will be the flowering laterals for the next growing season.

Male vines also should be dormant/winter pruned when the vine structure is visible. Male vines are recessive, and it takes them longer than female vines to produce a good number of flowers. The first several years, leave laterals with spurs to grow second-year spurs. In the fifth year, prune to remove all flowering wood from previous season. New growth should be thinned leaving only replacement laterals. Do not allow vines to grow into adjacent trees or other areas.

Flower and Pollination

Since the hardy kiwiberry is dioecious, both a male and a female vine are necessary for pollination and fruit set. While female vines produce fruit, male vines provide the pollen to pollinate female vines. Fruit set depends on the abundance of and well-timed availability of male pollen. Pollen should come in contact with the female stigma within three days of the female flower being fully open. If growing multiple female cultivars with different flowering times,  additional males with flowering times corresponding to those of the female plants will be needed. Nursery staff should match female cultivars to appropriate male pollinator plants prior to purchase.

Pollination is accomplished primarily by wind and some pollinating insects. Therefore, the male vine(s) should be located upwind so that, during flowering in May to June, prevailing winds flow through the male vine(s) before reaching the female vine(s).

Rainfall occurring during pollination will prevent the airflow dispersion of male pollen. If this occurs, cut flowers from a male vine can be brushed across female flowers. (See lead image showing photos of male and female flowers).

Harvest

Hardy kiwiberry fruit harvest is late August into September, depending on the cultivar. A refractometer will check the Brix or sugar content of the fruit prior to harvest. Brix is the total soluble solids content of a fruit that is determined by the index of refraction and measured by a refractometer. This measurement represents all the dissolved solids in a sample, including amino acids, enzymes, etc. The higher the Brix, the better the quality of the fruit and the more nutritionally dense it is. Nutritionally-dense foods have very high levels of vitamins, carbohydrates, minerals, enzymes, antioxidants, and trace minerals. Brix should be checked midday on a dry day as increased moisture content will lower the reading.

Once kiwiberry fruits have reached a Brix of eight, starches have fully changed to sugars and are ready for harvest. Fruits will continue to ripen after harvest, becoming sweeter and more flavorful. Harvested fruit should be kept cool in the shade and refrigerated as soon as possible. Fruits will be hard to touch and much less prone to mechanical, insect, or bird damage. Harvesting at a higher Brix is not recommended as shelf life will be shorter. Nor should harvest be delayed until the kiwiberries are soft to the touch. Picking them at this stage may damage the fruit. If the stem pulls away from the fruit, storage life is ended. Allowing the fruit to ripen further on the vine also exposes it to fruit fly and stink bug damage.

The Brix value of post-harvest, fully ripe fruit may range from sixteen to twenty-five or more. If harvesting kiwiberries that are riper and have a Brix higher than eight, are soft, or are growing in the shade, separate them from the firmer fruit as the riper fruit may release ethylene gas and accelerate the ripening of all the fruit in that container.

Refractometers may cost $100 or more. If you do not wish to make this investment, there is a method to visually judge if the sugars are close to maturation. Cut the fruit and look at the seed color. Seeds begin white; then turn cream, brown, and finally black. Once the seeds are black, the starch to sugar transition is completed.

Storage/Nutrition/Recipe Ideas

Place harvested fruit in the coldest part of your refrigerator in a vented, shallow, plastic container to avoid trapping moisture as the kiwiberries cool. Do not stack more than two layers. Fruit can be stored in your refrigerator for two weeks, or perhaps longer, if harvested at a Brix of eight. To consume, bring fruit to room temperature for several days. When skins begin to wrinkle and fruits become soft to touch, they are ready to eat. In addition to being a tasty treat, hardy kiwiberries are a nutritional powerhouse, loaded with antioxidants; Vitamins A, E, and B; and five times the among of vitamin C found in an orange.

Kiwiberries contain the proteolytic enzyme actinidin, which enhances the digestion of protein and, in some studies, was found to reduce colon transit time, especially in patients with irritable bowel syndrome (IBS). Actinidin also is found in pineapple, papaya, mango, and banana. Individuals with IBS should not overeat kiwiberries. If consuming a large amount of kiwiberry fruit, some people notice a prickly sensation on their lips or inside their mouths. This is caused by a protease in the fruit acting on mucous membranes. Anyone with a history of kidney stones should avoid kiwiberry fruit, as it contains oxalic acid. Finally, there is a condition known as "latex-fruit syndrome." Thirty to fifty percent of those who have a latex allergy have cross reactivity to many fresh fruits, including kiwiberries. Reactions can be mild to severe, including anaphylaxis.

Hardy kiwiberry fruit can be eaten fresh or sliced and dehydrated. Use the fruit in sorbets, cocktails, salads, and salsas with cherry tomatoes. Fruits also can be grilled on skewers. As heat increases the amount of acid in the fruit, basting skewers with orange juice will buffer the acid.  With a high sugar and pectin content, kiwiberries are perfect for jams and jellies. Do not add milk to any recipes with kiwiberries; the milk will curdle due to the presence of actinidin in the fruit.

Kiwiberry recipes

Insect and Disease Issues

Insect and diseases are few and some can be mitigated.

Western Flower Thrip - Damage to fruitlets occurs at blossom time, causing tiny caramel or darker colored bites/dots on fruit. These marks will grow in size as the fruit matures causing the fruit to not be usable as top-quality fruit in the fresh market. Thrip damage is only cosmetic and fruit can safely be consumed.

Thrips are drawn to the scent of the kiwiberry flower or other flowers in proximity, including dandelion, clover, and multiflora rose. Kiwiberry flowering occurs in late May-early June. In mid-May, hang yellow sticky traps under the vines. Check daily for the number of thrips seen on the traps. Thrips are reddish in color, 2/16 to 3/16 inches long and the thickness of a human hair. A loop/hand lens is needed for identification. Spraying vines with kaolin clay prior to or just after flower opening is effective to decrease thrip populations. The clay will irritate breather holes on the sides of the thrips. If it rains, re-application may be necessary.

Spotted Wing Drosophila (SWD) - This fruit fly can be an issue if ripening fruit to maturity on vine. By harvesting fruit at a Brix of eight and placing in cold storage, the pest can be avoided. Picking all ripe fruit and not leaving any on the vines or on the ground, also will help to decrease fruit fly populations. Damage looks like round yellow circles, more like a bite, with a hole in the center.

Japanese Beetles - These beetles cause some leaf damage but can be mitigated by leaving some of the new top growth that is standing upright during the summer months as a trap crop for the beetles.

Brown Marmorated Stink Bugs (BMSB) - While not a problem pest at present, they bear observation.  Bites are recognized as smokey, oval-shaped, and approximately 1/4” wide from the top to the bottom of fruit with a divot in the center and can occur even when fruit is harvested at a Brix of eight. More damage might be seen if fruit is allowed to ripen on the vines beyond a Brix of eight.

Spotted Lanternfly (SLF) - At present, no damage has been noted.  Research Extension personnel at the Pennsylvania State University are studying this pest and its potential damage to kiwiberries.

Phytophthora Root Rot - A clean raised bed with well-drained soil can prevent this disease.

Verticillium Wilt - Avoid planting kiwiberry vines in sites where other verticillium-susceptible crops,  such as strawberries, raspberries, potatoes, tomatoes, peppers, or eggplants, have been planted in the past five years.

Juglones - This is an allelopathic compound found in black walnut and hickory nut trees that can have a negative impact on kiwiberry vine growth.

Sooty Blotch - This is a fungal disease, appearing as a gray cloud on kiwiberry fruit, and is caused by water dripping onto a  spur. The cloud will come off by lightly wiping the fruit with water.  Well-pruned vines may mitigate the presence of blotch.

Flyspeck - This is another fungal disease. Tiny, dark dots appear on near-mature fruit. It usually occurs in late August when there are morning mists.

Russeting - This looks like an alligator skin brown area or scab on fruit. It occurs with wet conditions and when the flowers are wet and water drops on forming fruit.

Misshapen fruit may be the result of incomplete pollination.  Again, proper pruning can avoid this occurrence.

Wildlife Damage

Deer - Deer will browse new foliage. Pruning to keep the ends of laterals above the browse line (a deer’s nose) may deter deer damage. Deer fencing and deer deterrents are other options.

Rabbits - Rabbits can cause chewing damage on the base of the vine trunk.  Rabbit deterrents or tube tree protectors should be used.

Birds - During dry weather, birds may peck holes in fruit to access its moisture. Harvesting at a Brix of eight while the berries are still firm, can mitigate this issue.

Photo credit: Kiwi Berry Organics Co.