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Actinidiaceae, Actinidia indica, Kiwi fruit

June 4, 2011

I found this giant old Kiwi vine (see photo below) in someone’s yard in the Berkeley hills. It was full of flowers. The woman working in the garden said she was still eating fruit from last year’s harvest. Here’s a previous post on Actinidia polygama, a lesser known Kiwi relative with edible and medicinal properties, in addition to being used by cats, like catnip, as a mild narcotic.

 

A number of kiwi relatives with similar traits include the Arctic beauty kiwi (A. kolomikta), hardy kiwi (A. arguta), golden kiwi (A. chinensis), and velvet vine (A. eriantha).

 

The Actinidia genus contains over 400 species, most of which are native to East Asia, China in particular. Although the Chinese collected and used the fruit from the wild for thousands of years, the New Zealanders are responsible for growing and developing various kiwifruits.

 

Different Actinidia species vary widely, in color, shape, size and edibility.  Most kiwi vary in their cold hardiness. Until the mid 1880s the main cultivated kiwifruit was Actinidia chinensis var. hispida.

 

The first A. chinensis fruits in New Zealand were derived from a few seeds from a single fruit brought from China by a woman named Miss Isabel Fraser. It is thus highly possible that most commercial kiwifruits grown around the world originate fromt his single fruit, also indicating that the genetic base of the fruit is very limited.

 

One of the main reasons kiwifruit have seen so much commercial popularity is because they store so well, from 4-6 months at freezing. This makes shipping easier and the fruit can be transported around the world.

 

Kiwis are primarily grown in New Zealand, California, Italy, Japan, France, Chile, China, Spain, Greece, and Israel.

 

Kiwi vines are vigorous and long-lived. A healthy vine will typically grow 6-8 meters wide and 3-4 meters tall. The trunk becomes woody and can measure more then 20 cm in diameter when mature.

 

The vine is deciduous. Leaves are large, dark green, and hairy. As leaves mature they loose hairs on their upper surface and develop a distinct, white downy surface with light colored veins.

 

The flowers are large (16-20 cm diameter), creamy white, and often fragrant. Flowers are born singly or in small clusters. See Photo.

 

Plants are usually dioecious, meaning they need more then one plant in order to cross-pollinate and bear fruit. Hermaphroditic varieties do exist. Bees are the usual pollinators however, unfortunately for Kiwi growers, bees aren’t particularly attracted to the flowers, thus the presence of a nearby hive, or hand-pollination, will increase fruit-set and fruit-size.

 

Fruit size is proportional to the number of pollinated embryos, and thus the number of seeds. A kiwi needs more then 1000 embryos to be pollinated to become a good-sized fruit.

 

Male and female plants can be of different species and still cross-pollinate, but in order to do so their flowers must open simultaneously.

 

The fruit is oval, both the shape and size of a chicken egg. They have a brown, fuzzy skin. Inside are small, black, edible seeds embedded in a green flesh.

 

Kiwi are high in chlorophyll, thus the emerald-green hue of their flesh.

 

Interestingly, kiwi fruit doesn’t degrade after being opened, or exposed, as is the case with most fruits. This is also due to the high chlorophyll content.

 

Mature kiwi vines can produce 150 – 200 fruit. Maximum seasonal yields from a single is around 80 kilos.  Plants will typically begin to produce around four years old and reach maximum production at around ten years.

 

As far as cultivation goes: Kiwi are demanding plants in terms of soil quality, nutrients, and moisture. Vines are wind sensitive. Excess wind can snap branches. They can be grown in full sun or part shade, and are neither tolerant of high salt nor maritime locations. Primarily kiwi species prefer warm, temperate to subtropical climates. Plants can survive temperatures down to – 12 C, but not for extended periods of time. Young vines will be killed easily at these low temps. Kiwi require a period of winter chill to initiate leaf and flower bud opening during springtime. Vines grow best in deep, fertile soil. They can handle a wide pH range, from 5.5 to 7.2, however, pH adaptability depends on overall soil type. Kiwi like water, but not waterlogging, they require more moisture then many other fruit species.

 

As far as nutrition goes: Kiwi have a higher concentration of vitamins and minerals then most other fruits. They are very high in antioxidants and are a good source of fiber and one of the best sources of vitamin C. Kiwi have unusually high levels of vitamin E, possibly contained in their tiny black seeds.

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