Hardy kiwi: a potential crop for northern growers

Reprinted with permission from Great American Publishing

By Mary and Bill Weaver

Pennsylvania Correspondents


David Jackson has devoted 12 years of his time and energy to the hardy kiwi. His base of operations for research and development is in Danville, in Northumberland County, in northeastern Pennsylvania.


The hardy kiwi, according to Jackson, differs in several respects from its fuzzy cousin, found commonly in grocery stores. Hardy kiwi have smooth skins, and so don’t need to be peeled before eating. They are the size of a large grape to a small plum, and are sweeter than their better known cousins. In addition, the vines can take temperatures to -20˚ F., and need 200 hours of chill at 38˚F or lower before they will bloom and fruit, making them a potential new crop for northern growers.


Hardy kiwi are also nutritional powerhouses, with 10 times the vitamin C of citrus, and high amounts of potassium and vitamin E. They are bothered by few pests and diseases. “We get a few bird pecks,” said Jackson. “Deer can be a problem in areas with few forage crops. And Japanese beetles can be a problem with drought-stressed plants. Irrigated plants, though, can readily outgrow Japanese beetle damage, which is limited to the leaves.”


Half of the l2 acres at Kiwi Korners devoted to hardy kiwis are for research and development, and half are for production. “Growers can come and visit and get some hands-on experience here,” said Jackson.  “If you’re interested in growing the crop, it’s a good way to find out about system design and different cultivars.”


Jackson also grows pawpaws, ginseng, and strawberries, but, he says, “Kiwi is our forte, has been for quite a long time, and will be for the long haul.”


Hardy kiwi first came to the United States on clipper ships in the late l800s from China, Japan, Russia, and Korea. They were planted in arboretums, and remained a curiosity for decades. “There are less than l00 acres in the U.S. of commercial production, and only about l5 acres in New Zealand, and l0 acres in Italy and Japan,” said Jackson. “The research and development has not been put into the crop yet.” Kiwi Korners is currently conducting research toward risk minimization for new growers.


Kiwi Korners now has 50 different cultivars on-site from all over the world, procured from native habitats, nurseries, growers, arboretums, and seed companies. “We’re testing them to see how often, and how well, they produce in Pennsylvania,” said Jackson, “and to see how best to market the different varieties.”


In kiwis, male and female flowers are found on separate plants, and research is complicated by the fact that many varieties available from nurseries are misnamed as to sex and variety. “With kiwis,” said Jackson, “you don’t know for sure what sex or variety a given plant is until it starts flowering when it is six to eight years old.”


Jackson is currently working on genetic markers that will positively identify both the cultivar and sex while the plants are still young. “We’re currently working with the help of SARE on a research study entitled ‘Hardy Kiwi Pollination and Production,’ focusing on male cultivar vigor, flower dates, pollen viability, and female production rates,” commented Jackson.  “We need to match up the flowering dates in the males with those of the female varieties.  At this time, nobody knows what the pollen viability is in specific male cultivars.”

In choosing a location for growing kiwi, growers must keep in mind that most kiwi cultivars don’t like wet feet. Choose well-drained soil. “Up on a hill a bit can be good,” said Jackson. “We like some wind protection too.”


Before planting kiwi, Jackson first plants a cover crop of clover or oats to replenish the soil. After the cover crop is turned under, a ridge or raised bed is made for planting with a one-bottom plow.  “Aisles between the rows are planted with a low-grow fescue, as it will take the traffic, prevent erosion, and assist in moisture retention,” said Jackson.


Next, posts for the T-trellises are pounded in. Kiwi Korners’ trellises are top quality, “and we can pass them down to the next generation,” commented Jackson. “They should last 40 to 50 years. The kiwi plants themselves have been documented to the age of 60 years.”


In addition to treated posts, wire with a tensile strength of 230,000 pounds is used. “It doesn’t cost much more than ordinary galvanized wire,” said Jackson. “If the wire stretches and sags, you can have a difficult situation to work with.” T-trellises are used because the fruit is easiest to find and pick when it’s growing on the shoulders of the trellises. Kiwi Korners uses a five-wire trellis. Proper height of the T-bars is important. “At seven feet, you need ladders. At six feet, you can’t walk upright,” he commented. So Kiwi Korners has settled on 6 l/2 feet as a good height for the Ts.


Rows are spaced l5 to l6 feet apart, and plant spacing within the rows varies from l0 to l7 feet. They are still experimenting with spacing. “Nobody has yet pushed a lot of these cultivars as far as they will go,” said Jackson. “Before you buy mowing and tillage equipment,” he continued, “think very carefully about the space you have to work in. You don’t want equipment that will damage the fruit hanging on the T-bars, for example. We maintain our planting with hand pruning and a modified grape hoe. We do not use herbicides.”


After spending three years in a nursery bed spaced two feet apart, where the young plants are easier to care for, the kiwis are moved to their permanent positions. They are irrigated with micro-sprinklers, which are attached to the middle T-bar wire. Jackson suggests rows no longer than 480 to 500 feet because it’s much easier hydraulically for the irrigation.


“The droughts we’ve had recently have been the main hindrance to the development of this crop in Pennsylvania. They’ve been devastating, actually. We have enough water to keep the plants alive, but not enough for full production. We really need another well, and more mulching would also help. When it’s really dry, the fruits hang on, but the leaves drop, and then you don’t get the next year’s fruiting canes.”


Because of their limited water supply, Kiwi Korners is considering going to a wind machine or some kind of heat source for frost protection instead of sprinkling.  Jackson has found that after frost, some cultivars will reflower.


The basic pruning method at Kiwi Korners is single trunk system. “This is very important,” commented Jackson. “The plants will start to fruit up to two years earlier with a single trunk than they do with multiple trunks. Also, multiple trunks produce too dense a canopy that is undesirable for arbor management.”


Pruning is done twice a year. “Right after flower set, we take out canes, so we don’t get too much of a double canopy. Then pruning is done again in the fall. It’s important not to prune too close to spring, or the plants will bleed,” cautioned Jackson.  “We’re always pruning for next year’s fruit,” he continued. “Pruning directly affects fruit size, and we want the fruit on the shoulders of the T-bar where they are easy for the pickers to find. Plus, if you allow too much vegetation, that may lead to biannual fruiting. Also, we try, in our pruning, to separate each plant.”


Kiwi Korners has been fortunate to find a sale for their pruned canes. A wreath company buys them for 25 to 50 cents a pound. “It gives us some money for fertilizer,” commented Jackson.


The use of bees to pollinate kiwis can be difficult. It is necessary for a bee to visit a male flower first to carry its pollen to female flowers. Kiwi Korners sometimes puts pollen in the hives, so the bees will contact it before going to forage, taking some pollen grains along with them. They have also used rose dusters and other applicators to put the pollen right onto the female flowers.


“The male flowers are usually good for about 3 days,” said Jackson, “and the females for about 7 days. When a flower has been fertilized, within 48 hours, the anthers will darken, the petals will push back, and the actual fruit itself turns from a yellowish to more of a greenish color.” Both sexes start flowering at the beginning of June in their location.


The fertility program at Kiwi Korners consists of natural materials. “I could recommend compost on raised beds, leaf mulch, and rock phosphorus,” said Jackson. “We’ve had to learn the hard way. Plants can be killed by too much nitrogen. But the plants are very easy to fertilize, since the roots are so close to the surface.”


“Kiwi can be harvested simultaneously with each hand, by snapping the individual fruit stems from the spur and placing the fruit in a picking bucket,” said Jackson. “On occasion, the stem will pull away from the fruit. In this case, it is not included with the harvest due to ethylene causing the rest of the fruit to ripen early.”

Time to harvest is determined by the level of “brix”, or residual sugars, in the ripening fruit. “We pick at 9 to 11 brix,” explained Jackson.  By the time the fruit have “cured”, they will be ripened to about 21 brix when they get to the store shelf. “If you wait to pick until a higher brix level, there’s a greater chance the stem will pull off the fruit.” A picker can pick about 20 pounds of hardy kiwis an hour. Then the harvested fruit is put in a walk-in cooler to cure naturally for 2 weeks.


On the West Coast, a different harvest system has been used. Out there, they pick at 6.5 brix, when the fruit are rock hard. “Then they hold the fruit in a CA room and ripen them with ethylene,” said Jackson. “The customers did not like the resulting fruit. We find it more advantageous to let ours cure naturally, which produces a longer shelf life and a higher nutritional value.”


Kiwi Korners started marketing their kiwis 3 years ago under the name “Kiwi Berries.” In upscale grocery stores and natural food stores, they sell the kiwis packed in 6-l/2 oz. clam shells, where they sell for $l.99 to $2.99 each. Their label says “Naturally Grown,” rather than “organic,” even though they use no pesticides.  The clamshells are marketed through HortiFruit in Florida, which is based in Santiago, Chile. The fruit are shipped from Maine to Texas. “Our biggest problem is getting more growers,” said Jackson. “ We have the marketing for the product, but without more product, we can’t get the whole thing going to maintain the market.”


A second way the hardy kiwis are marketed is through farmers’ markets, where they are sold in half pound or pound -size fiber containers at a lower price. The fruit is picked at a higher brix for these markets.


Some of Kiwi Korners’ fruits are also sold as puree. They move one to two tons of puree a year. “After the fruit has had one or two frosts, we strip the vines of the remaining fruit for puree,” said Jackson. “We’ve been experimenting with uses for it. A company near State College is marketing value-added products made with our “Kiwi Berries.”  Since the brix is so sky-high, we would like to get wineries involved. We also make jams, sauces, and marinades.  “Also, kiwi is the world’s greatest meat tenderizer. Put two spoonfuls on steak overnight,” said Jackson, “and you have baby food in the morning.”


Jackson is working with several particularly interesting cultivars. One is a sport plant brought to Kiwi Korners from a Virginia test site. “It has a shelf life of up to 30 days, and a very high brix – 3l brix. It tastes like a super-sweet melon ball,” commented Jackson.  Another cultivar, Jumbo Royale, is from Michigan State University, and has a very large fruit for a hardy kiwi, the largest in their collection. “It’s a two-bite fruit,” said Jackson. “It’s very low acid, with a flavor like a cross between banana, strawberry, and kiwi.”  A third is a red -on- red cultivar from New Zealand with red skin and red flesh. “This variety is also being test trialed on a 40-acre island site in the middle of the Susquehanna River due to the moderated temperatures and water availability,” said Jackson.  “Kiwi Korners’ focus is the development and promotion of multi-cultivar hardy kiwi as an alternative, sustainable fruit crop and to facilitate information between academia, growers, and the market place,” said Jackson.  “We are available for consultation and on-site visits with emphasis on teaching growers about kiwi cultivation, including site evaluation, complete system design, cultivar evaluation, and niche marketing. Please contact us for further information at (507) 275-878l, email at kiwikrnr@sunlink.net, or visit our web site at www.kiwiberry.com.”