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By Tim Hartmann |
This article is part of a series entitled “Vines for Texas Landscapes” coordinated by Bill Welch, TAES Extension horticulturalist.
Unlike grape or blackberry, kiwifruit is a relatively new crop to the United States, especially in the garden. In fact, many people are unaware that kiwifruit are borne on vines. Most people think only of the strange fuzzy fruit with green flesh that have become commonplace in supermarket fruit displays over the past three or four decades. Actinidia deliciosa (Actinidia chinensis var. deliciosa) produces the green or “fuzzy” kiwifruit that we have become so accustomed to, and is only one of many species in the Actinidiaceae family. However, there are many other forms of kiwifruit.
Depending on botanical classifications, there are 66 species of Actinidia, most of which are native to China and surrounding Eastern Asia. Most of these tend to be rapid-growing woody vines, with male and female flowers produced on separate plants (dioecious). Hardy kiwifruit or “kiwiberry” (A. arguta) is native to the northern regions of China and Japan, and therefore has much greater winter hardiness. Its much smaller (1-1/4” long) smooth fruit can be produced as far north as the upper Midwest. A. kolomikta, commonly referred to as Arctic kiwi or variegated kiwi, is another Actinidia species with great winter hardiness. While the small fruit of this species are edible, it is more commonly grown for its ornamental foliage. ‘Arctic Beauty’ is a male selection of A. kolomikta, and is popularly grown for its beautiful variegated foliage. Both A. arguta and A. kolomikta have some tolerance to heat, but are better suited to the northern portions of Texas.
Kiwifruit History
Like many other plants, kiwifruit has a rich and unique history. Despite having been grown for thousands of years in its native China, the rest of the world had no knowledge of this incredible plant until early in the last century. It was not until 1904 when Isabel Fraser, a teacher, brought seeds of the green kiwifruit (known in China as yang tao) back to her own New Zealand. Six years later, the resulting seedling vines began producing their first crop. In 1920, plants referred to as “Chinese gooseberries” appeared for sale in nearby nurseries. Four years later, nurseryman Hayward Wright selected and began propagating what would eventually be known as the cultivar ‘Hayward.’ Interestingly, ‘Hayward’ still remains the most prevalent cultivar more than 90 years later.
In 1934, the first commercial orchard was planted on the North Island near Taraunga. By the early 1950s, England began to receive its first shipments of fruit. In an effort to increase marketing in the United States in 1959, the fruit was renamed “kiwifruit” for its similarity in appearance to the kiwi, New Zealand’s national bird. In 1967, the first ‘Hayward’ plantings were made in Central California, with the first commercial crop harvested in 1977. In addition to their novel nature, kiwifruit have historically benefited from marketing success because of their high Vitamin C content. Once known in China as the “king of fruit” for this reason, green kiwifruit typically contain two to three times as much ascorbic acid as the orange, which has long been considered a standard for this nutrient. Today, production totals 3.26 million metric tons (FAO, 2013), ranking kiwifruit 20th among all fruits. The largest producers include China, Italy, New Zealand and Chile, in order of total yield. The United States ranks 10th globally, with nearly all of the production taking place in California.
Golden Kiwifruit
The past several years have seen the emergence of a completely new form of kiwifruit in the produce aisles of America. Golden kiwifruit, Actinidia chinensis (A. chinensis var. chinensis), is the second most economically important species of kiwifruit. As the name suggests, fruit have yellow or golden flesh that is surrounded by nearly smooth or fuzz-less skin. The golden kiwifruit is new, even in the “kiwi world,” having only been in production since the end of the 20th century in New Zealand. Since then, it has spread to the other major kiwi-producing regions, especially Italy.
Production of kiwifruit has been attempted east of the Rocky Mountains. During the mid-1980s, several orchards of ‘Hayward’ were planted from the Carolinas down into the Coastal “deep” South. Although the plants tended to grow well, reproductive growth was reportedly poor. According to Auburn University professor Dr. Jay Spiers, ‘Hayward’ “simply wasn’t adapted to the Southeast.” In the early 1980s, two cultivars of golden kiwifruit selected from seedlings collected in the wild were developed at the Institute of Fruit and Tea, Academy of Agricultural Sciences in the Hubei Province of China. These selections, known as ‘Jinnong’ and ‘Jinyang,’ were imported into Alabama for field trialing in 1994 by Auburn University researchers.
After more than a decade of successful production in Central Alabama, these cultivars were jointly released by the Institute of Fruit and Tea and Auburn University in 2008 as ‘AU Golden Dragon’ and ‘AU Golden Sunshine,’ along with their respective male pollinizers (‘CK-3’ and ‘AU Tiger’). At the same time, ‘AU Fitzgerald,’ a seedling selection of ‘Hayward,’ was also patented as a new green kiwifruit cultivar for the Southeast. These cultivars have become available through The Wildlife Group, a wholesale nursery in Tuskegee, Ala. Commercial production of golden kiwifruit began in the 1990s in New Zealand and later Italy, under the Zespri brand. Golden kiwifruit has continued to grow in popularity as it has begun to appear in produce aisles across the U.S.
Kiwifruit in the Garden
In the garden, kiwifruit may be used as beautiful vines, while also offering the possibility of exotic fruit. The very large (up to 8” wide), dark green heart-shaped leaves are probably most similar to that of bleeding heart (Clerodendrum). Bold foliage commands attention and can be used to help create a tropical appearance. The young shoots of A. deliciosa, is truly a sight to behold when the innumerable tiny hairs (trichomes) glisten with dew in the first rays of morning sun. Forms such as ‘Arctic Beauty’ with highly ornamental foliage are available, but many of these are not grown for their fruit.
While kiwi vines may not be a significant source of fall color — leaves quickly transition from green to brown — the new shoots and young leaves may appear “dipped” in maroon [anthocyanins], as the plants are first conditioned to cooler weather in the early fall. Spectacular displays of creamy-white to yellow flowers (3/4”) in late March through late April can be very fragrant (depending on cultivar) and are frequented by bees. Vines can easily cover a small- to medium-size trellis in a single season, providing a cool oasis of shade during the hot summer afternoon. Kiwifruit vines do not produce tendrils or aerial rootlets, but rather climb by tightly twining around their support similar to Wisteria or morning glory (Ipomoea). A large golden or green kiwifruit vine has the potential for up to 200 pounds of fruit, so sturdy structures are needed. While hardy kiwi are often trained onto a vertical wire trellis, an overhead pergola type trellis is ideal for the more vigorous green or golden kiwifruit.
Cultural Requirements
Like most fruiting plants, it is imperative that kiwifruit be planted in a soil with excellent drainage. Plants will not tolerate heavy clay soils and are highly susceptible to the fungal pathogen Phytophthora that causes decay of the roots and crown. For sites with poorly-drained soils, construction of a two- to three-feet high berm with gently sloping sides can be used to facilitate drainage. Kiwifruit prefer acidic soils (pH of 5.5 to 6.5), making them better candidates for the eastern portion of Texas (generally IH 45 and east). Plants growing in soils that have a pH of 7.2 or greater will typically display symptoms of severe micronutrient (especially iron and manganese) deficiency. However, kiwifruit are not quite as sensitive to alkaline soils as blueberry. Incorporation of composted pine bark or peat moss along with the supplementation of chelated iron may afford planting in more neutral to slightly basic soils common in Central Texas.
While the more Northern-suited hardy kiwi may benefit from partial shade, full sun is preferable for the large-fruited species for maximum production and quality. In terms of cold tolerance, the gold and green species of kiwi are reportedly hardy to about 10°F, landing them roughly in about the same group as figs and pomegranates. Winter chilling requirements are believed to be in the 700 to 900 hour range for maximum fruit production. With their large leaves and brittle shoots, kiwifruit are also susceptible to damage from wind. Sheltered sites are preferred, but hedges of evergreen shrubs or trees (such as juniper or holly) can be used to provide screening from wind. Kiwifruit are heavy drinkers and feeders. Plants have a relatively high requirement for good quality (low in salinity) water throughout the growing season. They also require relatively heavy amounts of nitrogen, especially during establishment.
Plants may be purchased as either bare-root or containerized, and may be grafted or “on their own roots.” Plants are typically spaced 10 to 15 feet apart. The vines are usually cut back close to the ground, after being allowed to grow the first season, to encourage a strong root system. In the second year, a single shoot is selected and trained to the top of the trellis, where it is cut back to encourage it to fork. The two resulting shoots are then grown in opposite directions down the length of the trellis to form the cordons or horizontal trunks. From the cordons, lateral shoots will grow and will serve as the fruiting canes for next year. A well-tended kiwifruit vine can produce a small crop in the third year after planting, but the first significant crop can usually be expected by the fourth year. Pruning of mature plants involves the removal of dead and diseased wood as well as canes that bore fruit in the previous year. Male vines are cut back severely after bloom to encourage new growth and make more room for female plants. As with grapes, one-year-old (last year’s) wood is preferred for production.
As mentioned earlier, kiwifruit are dioecious; therefore a sufficient number of male plants with bloom times that coincide with that of the females’ must be present in close proximity. For a smaller planting in the home garden or orchard, one male will usually be sufficient, unless multiple female cultivars with very different bloom times are used. Kiwifruit are predominately insect-pollinated, so in the absence of bees, hand-pollination can help improve yield and fruit size. Kiwifruit have relatively few pest and disease problems that pose a serious threat compared to other fruit crops, such as peach and apple. Scale insects and spider mites (summer) can occasionally be problematic. In exceptionally coarse sandy soils, root-knot nematodes can sap plant vigor and yield. A relatively new bacterial canker disease called P.S.A. has devastated many commercial plantings in New Zealand and Italy, but thus far has been kept out of the United States through quarantine.
Kiwifruit are climacteric, that is, they can be picked at an immature (green) state and are capable of ripening off the vine. Several parameters for determining harvest time are used, but fruit are typically picked when they first become barely soft. This typically occurs in September for golden kiwifruit in Texas and October through early November for green kiwifruit.
Kiwifruit in Texas
In 2011, approximately 30 plants of the Auburn varieties were planted as a small trial on the Stephen F. Austin State University campus in Nacogdoches, Texas. The plants proved to be right at home in deep East Texas, and rapidly began to outgrow their simple trellis. In the fall of 2014, professor emeritus and fruit enthusiast Dr. David Creech harvested what is believed to be the first-ever crop of golden kiwifruit in the state of Texas. Although the crop was light, consumer evaluation reports were very favorable.
In 2015, approximately 875 pounds of delicious golden fruit were harvested, primarily from eight plants of ‘AU Golden Dragon.’ “If one were to extrapolate this kind of yield out to a larger scale, we would be looking at over 40,000 pounds per acre,” Dr. Creech remarked. The 2016 season saw a very light crop of gold, although a decent and first-ever crop was harvested from ‘AU Fitzgerald.’ According to Creech, much of the reduction in yield can be attributed to very little bee activity during bloom time as well as insufficient winter chilling. Still, there is plenty of hope for the future.
