Kiwis


Posted on 18 March 2001

What's brown and fuzzy all over and green inside? Well, the kiwi, of course. This Chinese fruit was popularized when it was imported into New Zealand, renamed kiwi instead of Chinese gooseberry, and developed as an export crop. Today this fruit crop is grown in many places worldwide, but there is more than just the kind found at the grocery store. To learn more about kiwi fruit, read this article...


‘Hayward’ kiwifruit.The kiwi is a flightless bird native to New Zealand, a name New Zealanders like to call themselves, and also a fruit – one of the very few temperate fruit crops to have been domesticated this century. Native to the high grasslands, low scrub and forests of China and Russia, Actinidia deliciosa was still just a wild plant in China (a delicacy called Yang Tao) at the turn of the century. In 1904 seeds were imported into New Zealand (and about the same time into the U.S. and Europe), and after a little selection, the fuzzy brown fruits with green flesh were renamed kiwifruit (from Chinese gooseberry) and developed into a successful export crop. Today the kiwifruit is an important commercial crop in New Zealand, the United States, Italy, Japan, France, Greece, Spain, Australia, and Chile, with the more than a million tons of fruit per year distributed worldwide. 

Commercial kiwifruit on the vine, near Tauranga, NZ.Most of the kiwifruit grown in commercial orchards outside of China are a single variety, ‘Hayward,’ descended from two female plants and one male plant derived from a single introduction of seed. Grafted plants were first sold in the 1920’s, standardizing the type of fruit produced. ‘Hayward’ has large, oval fruits with bright green flesh that lack a hard or woody core. 

But this is NOT the only type of kiwifruit. The genus Actinidia contains about 60 species. All are perennial, mostly deciduous, climbing woody vines native to Asia, but their fruit is quite variable. Some produce fruits singly, others in bunches. The fruits vary in size, shape, hairiness, and color. The flesh can also vary in color, juiciness, texture, and taste, with some fruits being basically inedible while others are considered better than the standard kiwifruit.

 

Fruit diversity in Actinidia, with the commercial kiwifruit, A. deliciosa ‘Hayward’ for comparison.

1  A. rufa

5  A. latifolia

9  A. arguta

13  A. guilinensis

2  A. melanandra (red kiwi)

6  A. indochinensis

10  A. fulvicoma

14  A. setosa

3  A. glaucophylla

7  A. chinensis ‘Hort16A’

11  A. deliciosa ‘Hayward’

15  A. chrysantha

4  A. chinensis

8  A. macrosperma

12  A. arguta var. purpurea

(purple kiwi)

16  A. eriantha

Photo from Ferguson, A.R. 1999. New temperate fruits: Actinidia chinensis and Actinidia deliciosa. p. 342–347. In: J. Janick (ed.), Perspectives on new crops and new uses. ASHS Press, Alexandria, VA. Online at http://www.hort.purdue.edu/newcrop/proceedings1999/v4-342.html

Fruit of the hardy kiwi, A. arguta.In the late 1980’s a new commercial, yellow-fleshed variety was created in NZ by crossing the conventional A. deliciosa with A. chinensis, which comes from warmer parts of China. This ‘Gold’ variety has a sweeter, more tropical taste and higher vitamin C content than the common ‘Hayward’ variety. It has the same seed pattern as ‘Hayward,’ but its skin is hairless and much more tender. NZ scientists are working on breeding a whole range of different kiwifruit, some with orange, yellow, purple or red-flecked flesh. Fruit with hairless green or bright yellow skins vary from small, bite-sized morsels to one that resembles a cucumber. Crosses with A. melanandra have produced large crops of small but very sweet fruit with very good flavor and red flesh. They’re still working on utilizing A. eriantha that has 10 times more vitamin C than the ‘Hayward’ variety, but has tiny, tasteless fruits.

The standard kiwifruit found in your local market is NOT a tropical fruit as many consumers believe, but does require a long growing season (over 200 days) and cannot tolerate winter temperatures below 10ºF. But this doesn’t mean you can’t grow kiwifruit here in Wisconsin. Some species of hardy kiwifruit will survive temperatures as low as -40ºF, and some produce fruit that are even sweeter and more flavorful than the commercial kiwifruit. 

Fruit of the hardy kiwi, A. arguta.The two most commonly available hardy species are A. arguta and A. kolomikta. A. arguta (with common names including Hardy Kiwi, Bower Vine, Dessert Kiwi, Cocktail Kiwi, Tara Vine, Yang Tao) produces smooth and hairless, grape-sized fruit in reds and greens with a sweet flavor similar to the commercial kiwi. A. arguta has a strong-growing vine to 40 feet, with dense, dark green foliage. In its native Asian habitat the vines typically grow wild in trees, climbing as high as 100 feet. When fully dormant the plants can withstand -25°F (Zone 4), but they still need a long growing season (about 150 frost-free days) and must acclimatize to cold. Sudden temperature drops may cause trunk splitting and subsequent damage to the vine. Young shoots, flower buds, and flowers are vulnerable to frost injury, and can be damaged in as little as 30 minutes at 30°F. The plants can be grown in large containers, however, to provide suitable temperatures, but do need a certain amount of winter chilling. There are many varieties of A.arguta; probably the most popular is ‘Ananasnaya,’ commonly called ‘Anna.’ 

Leaves of the male super-hardy kiwi, A. kolomitka.Super-hardy kiwi, A. kolomikta, is even more cold hardy, tolerating temperatures to -35 or -40°F (Zone 3) but is much less vigorous than A. arguta, growing only to about 20 feet. It produces fruit similar to A. arguta but somewhat smaller. ‘Arctic Beauty’ is a commonly-offered variety (for example, see Jungs Seeds). The male vines develop attractive pink, white and green variegated leaves the second to third year after planting. 

All species appear to be dioecious (with both male and female parts on a single plant), but are functionally monoecious (male and female parts on different plants). Flowers on male vines produce viable pollen but lack proper female parts, while the flowers of female vines produce fruit but don’t have viable pollen. The transfer of pollen from male to female flowers is essential for fruit production. One male vine may supply enough pollen for four females. The one exception is the self-fertile variety ‘Issai,’ which tends to have small fruit and relatively low vine vigor.

Trellised kiwifruit vines, near Tauranga, NZ.All kiwifruit plants require a wall, fence, substantial trellis, other permanent place to grow upon (even in trees) since the long-lived plants climb by twining. The vines do best in a sunny location with well-drained, somewhat acid (pH 5 - 6.5) soil. Vines grow and produce best in areas sheltered from constant or gusty winds. Winds of only 10 to 15 miles per hour or can break developing shoots and reduce vine growth and production. Tall hedges are used in New Zealand kiwifruit orchards to help reduce wind damage. The plants need constant moisture, but not soggy soil, and are heavy nitrogen feeders. Winter pruning is necessary for good fruit production.

Hardy kiwis don’t have many pests or diseases, but deer will browse on the leaves and rodents may attack the roots. And cats may damage the plants since they love to rub against the catnip-scented trunk – this activity will damage new shoots emerging in the spring on small plants! 

Flowers of A. arguta.The white to cream flowers are produced in the leaf axils, singly or in small groups for a period of several weeks in late spring. Fruit set depends on adequate pollination by bees or other pollinators. Female flowers are viable and receptive to male pollen up until 9 days after opening, while the pollen from male flowers is viable for only 3 days after opening. Home gardeners can hand pollinate to guarantee fruit set. Pick a freshly opened male flower and rub it on a viable female flower for a second or two. One male flower can be used on as many as five female flowers before discarding it.

Hardy kiwifruits ripen in late summer to late fall, depending on the cultivar and local weather conditions. The fruits drop or come off easily when they are fully ripe. However, they are usually picked at the mature-ripe stage and allowed to ripen off of the vine as for the commercial types. 

Ripe commercial kiwifruit.Store-bought kiwis are ready to eat when slightly soft to the touch. The firmer the flesh the more tart the flavor will be. To speed up the ripening process, place the fruit in a bowl with ethylene-producing fruits such as apples, pears or bananas.

These nutritionally dense fruits have more than twice the vitamin C of an orange (more than twice the USDA recommended daily allowance). A large kiwifruit averages only 45 calories, contains no fat, has very little sodium, and has as much potassium as a banana.

You can eat kiwis in more than fruit salad or as a snack. I topped mixed spring greens with sliced kiwi and chopped macadamia nuts and drizzled everything with raspberry viniagrette for a deliciously different salad. Blend them into a tropical-tasting strawberry-kiwi smoothie (place 3 peeled kiwis, 1 peeled banana, 3/4 cup pineapple juice and 1 cup frozen strawberries in a blender and process until smooth).

Or try them in this authentic NZ recipe:

Pavlova

Pavlovas come in a variety of shapes, sizes, and fruit toppings.This classic Aussie-NZ dessert was created by a Western Australian chef in honor of the Russian ballerina Anna Pavlova. It consists of a meringue crust topped with whipped cream and fresh fruits such as kiwis, strawberries, etc. but your imagination is the only limit on the form a pavlova can take. Celebrate ANZAC Day (April 25) with your own pavlova this year!

3 egg whites

9 oz. castor sugar (1 1/3 cups superfine sugar)

salt

1 tsp vanilla extract

1 tsp vinegar

whipping cream

sliced kiwifruit (or other fruit)

Beat egg whites and a pinch of salt until quite stiff. Fold in sugar, add vanilla and vinegar. Prepare a greased tray with greased paper. Spoon the batter onto the greased paper in a large circle (8 to 12" diameter), building up the edges to form a bowl shape (the sides can be as high or as low as you want, to accommodate more or less filling). Or make several smaller crusts for individual servings. Bake very slowly about 1 to 1½ hours at 250°F or until only very lightly browned. 

Just before serving fill with whipped cream (which can be flavored with your choice of liquor) and arrange fruit on top. 

Enjoy!

Additional Information:

– Susan Mahr, University of Wisconsin - Madison

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