Actinidia - kiwi berry

The most widespread species is Actinidia deliciosa (Kiwi fruit) derived from Actinidia chinensis, native to the Yangtze River valley in middle China. At the beginning of the 20^th century it was brought to New Zealand, where its name was changed from Chinese gooseberry (which seemed to put off some people) to Kiwi after the supposed resemblance of the fruit to the national bird, the flightless Kiwi. Nowadays Actinidia deliciosa is widely cultivated for its edible fruit in warm temperate zones of Italy, Spain, Greece, France, New Zealand, the USA, Japan, Israel and Chile. Unfortunately, all cultivars of Kiwi fruit are frost tender and freeze at about -10^oC. The most frost hardy cultivar of the species, a hermaphrodite form 'Jenny', can withstand frost and cold to -15^oC, but its fruit is small and insipid.

Actinidia arguta 'Weiki' - female flowers (photo Sz. Marczynski)

Actinidia arguta 'Weiki' - male flowers (photo Sz. Marczynski)

 

Actinidia kolomikta 'Adam' (photo Sz. Marczynski)

Actinidia arguta (Hardy kiwi, Tara vine) and Actinidia kolomikta (Arctic beauty kiwi) are much more frost hardy than Actinidia deliciosa, and therefore may be cultivated in the Polish climate. Actinidia arguta, depending on a variety, can withstand temperatures from -23^oC down to -35^oC, and Actinidia kolomikta tolerates temperatures even down to 40 degrees below zero. Both plants are mainly regarded as ornamental climbers, ideal for covering fences, walls, pergolas and arbours owing to their twining growth habit. They also bear tasty fruit, although much smaller than the kiwi fruit - more or less the size of a grape.

In fruit gardens and orchard plantations the varieties of Actinidia arguta, also known as MINI KIWI or Hardy kiwi, are considered to have the biggest potential thanks to their relatively large, tasty berries. In order to produce fruit, Tara vine needs a long growing season – around 150 frost-free days. An adult plant can yield between 10-20 kg of berries. This rampant climbing plant can grow up to 30-50 m high in its homeland, while in a cooler climate, in Poland for instance, it reaches up to 4-8 m high. Young shoots are brown and change colour to grey with age. Large ovate green leaves turn yellow in autumn and fall shortly afterwards. The following varieties of Hardy kiwi are available in Poland:

 

• 'Ananasnaya' - considered the best cultivar for commercial cultivation.
  

• 'Geneva' – an American female cultivar bread in the Geneva Research Station, Geneva New York. It's the earliest-ripening variety of the species, the fruit ripen from mid September to October. Medium-sized rounded berries (3 cm long and 2 cm across) develop a reddish-brown bloom when in full sun. They are very tasty: sweet with a honey flavour and a light aroma. Ripe berries get soft quite quickly and fall, especially when the plant doesn't receive enough water. A very prolific cultivar, it starts bearing fruit in the third or fourth year after planting. It withstands frost and cold to -30^oC. 

• 'Issai' – a Japanese dioecious self-pollinating form. Berries ripen in mid October. This prolific variety bears quite tasty, medium-sized, oblong (2,5-4 cm long and 1,5-2,5 cm across) green fruit, already in the first year after planting. It sustains frosts down to about -25^oC. Its compact growth habit (up to 3-4m high) makes it ideal for smaller gardens. Suitable for warmer regions.

• 'Jumbo' – an Italian, female form bearing exceptionally large oblong slightly elongated (up to 5cm long and 3cm across) green-yellow fruit. The biggest berries can weigh up to 30g. The fruit is tasty sweet without a distinct aroma and long-lasting, though it can sometimes crack at the base. Berries ripen form late September to mid October. A prolific variety that starts yielding fruit in the third or fourth year after planting. It grows up to 8 m high and withstands cold to -28^oC.

• 'Ken's Red' – a New Zealand female form bred as a cross of Actinidia arguta var. cordifolia and Actinidia melanaudra. Large (up to 4 cm long and 3 cm in diameter) durable tasty berries, though without a distinctive aroma, are purple red in full sun and green in shade. They ripen from mid September to mid October. Ripe berries don't soften excessively what makes them suitable for transport. Withstands frost and cold to -25^oC.

• 'Kokuwa' - a Japanese, self-pollinating form with tasty lemon-flavoured durable fruit (Mini Kiwi) ripening in late September-October.

• 'Purpurna Sadowa' – a Ukrainian female form, most probably selected from Actinidia purpurea seedlings or obtained by crossbreeding Actinidia arguta and Actinidia purpurea. Tasty and long lasting medium-sized (3.5 cm long and 2.5 cm across) oval berries, purple red when in full sun and green in shade, ripen from mid September to mid October. Bears fruit in the third – fourth year after planting. Withstands temperatures down to -25^oC.

• 'Rogów' – a Polish female form selected in Arboretum in Rogów. Quite tasty medium-sized (2,5-3 cm long and 2-2,5 across) green fruit ripens from the end of September till the beginning of October. A very prolific cultivar, it starts bearing fruit in the third or fourth year after planting. Withstands frost and cold to -30^oC.

• VITIKIWI - an attractive, prolific cultivar that sets fruit without pollination (parthenocarpic). Starts bearing fruit in the 1^st-2^nd year after planting. Its tasty, green, usually seedless fruit ripen in October.

•  'Weiki' - a German dioecious cultivar. Male specimens are good pollinators for all cultivars of Tara vine. Female specimens are very prolific. Tasty medium-sized (about 2,5-3 cm long and 2-2,5 cm across) berries ripen in October but they don't fall. They are normally green but develop a dark brown bloom when exposed to direct sunlight. Handsome lustrous dark green leaves on red stalks give the plant an attractive appearance making it a happy marriage of utility and ornamental value. It starts bearing fruit in the third or fourth year after planting. Tolerates temperatures down to -30^oC.

Actinidia arguta 'Weiki' - berries (photo Sz. Marczynski)

 

Actinidia kolomikta (Arctic beauty kiwi) requires around 130 days without ground frosts in order to yield fruit. Berries ripen in August and fall immediately, which reduces significantly its potential for widespread consumer use.

Actinidia kolomikta 'Adam' - leaves (photo Sz. Marczynski)

The fruit is oblong, about 2cm long, tasty, sweet and succulent. The plant can yield up to 10kg of fruit. Cats are very fond of this shrub and can damage it by scratching or biting the leaves, so it’s better to secure the base with a net for the first three years. When fully hardened, it can withstand frost and cold even down to 40 degrees below zero.

There are several varieties known in Poland:

• 'Adam' – a very ornamental Polish male form with beautifully variegated foliage and attractive male flowers; a good pollinator for all cultivars of Actinidia kolomikta. Selected by Szczepan Marczynski and introduced to the market in 2001.

• 'Dr Szymanowski' – a Polish dioecious variety, remarkable on account of its variegated foliage and tasty fruit. Very prolific, it starts bearing fruit in its fourth or fifth year after planting.

• 'Sentyabrskaya' – a prolific Ukrainian female variety with attractively variegated foliage. In the third or fourth year after planting it starts yielding tasty slightly aromatic fruit that ripens in August.

Actinidias best propagated from stem cuttings taken in midsummer, or by layering. It should be grown in a container for 1-2 years to ensure good rooting before planting it out into its permanent position in the garden.

 

Cultivation

If you choose a dioecious variety, you will need to plant both male and female forms at close proximity (3-5 m at best). When planting a larger number of Actinidia it's enough to plant one male form for every 5-8 female plants. These can be the specimens of different cultivars but should belong to the same species.

The male plants ought to be evenly distributed among the female plants and come into flower at around the same time. If you have room for only one plant, it’s best to put both a male and a female form in one hole, or, alternatively, choose a hermaphrodite variety(it may be unreliable) or graft a male stem on a female plant. Actinidia arguta blooms at the turn of May and June, bearing small (1-2 cm in diameter) white flowers. The flowering period of Actinidia kolomiktastarts 7-14 days earlier. Its flowers of are a bit smaller and have a faint lemon scent.

Male flowers, borne in racemes of more than a dozen, have well developed stamens with pollen which remains fertile for 3-4 days, while female flowers are borne individually or in clusters of two or three, and have a large, well-developed pistil surrounded by barren stamens. They can be pollinated for 9-10 days. The number and the size of berries depend on the good pollination. It's vital that both female and male flowers bloom at the same time. They are essentially pollinated by bees and other insects and, to a lesser extent, by wind. Unfortunately Actinidia flowers are relatively unattractive to insects, so need a lot of them to ensure good pollination. In the absence of insects you may also try hand-pollination. Pick a freshly opened male flower and brush it for 1-2 seconds against a female flower. The pollen of one male flower is sufficient to pollinate about 5 female flowers.

Actinidias in general, and more sensitive species and cultivars in particular, grow best in warm, sunny, wind-sheltered locations. You should avoid frost hollows, because Actinidias are sensitive to spring frosts. When planning where to plant your Actinidia, you should remember that large lakes and rivers are natural reservoirs of heat. Likewise, the walls give off some heat and thus increase the chances of winter survival of these tender plants. West and southwest positions, shaded till mid-morning, prove to be the best location. Actinidias are most vulnerable during the first 3-4 years after planting, so in that period you should pay particular attention to providing appropriate protection against cold, e.g. by putting mulch around the base of the plant. I wouldn't recommend cultivation in polyethylene tunnels, because such plants tend to start their growing period earlier what makes them more sensitive to late season frosts.

Actinidias grow well in various soils, although they prefer soil that is rich in organic matter, but light, with thickness not less than 1-1,5 m. It should be well drained, moist, but not waterlogged, and somewhat acid (pH 5-6.5). Since Actinidias are shallow rooted plants, you should avoid loosening the soil. When planting out, the plants should be put to the ground at the same level they used to grow in a pot, into a hole dressed with compost or well-rotted manure. Actinidias need large volumes of water during the entire growing season and it's especially important to water the plants regularly in the time of intensive growth or during the hot weather spell. They also require balanced feeding with macro and micro nutrients. Start fertilizing in the second year after planting; sprinkle the soil at the base of the plant, 20-80 cm away from the trunk.

Pruning

When used as an ornamental plant, Actinidia can be left to grow in an unrestrained manner, with only occasional trimming of errant branches. However, such a plant will start yielding fruit later and it will be of poorer quality.

In order to achieve the best crop, you should specially train your Actinidia and prune it hard, bearing in mind that berries are borne on the stems that are trained horizontally and are 2-3 years old.

In commercial plantations Actinidia is usually trained along a T-shaped trellis (picture A below), as it ensures the best crop. In amateur cultivation it's best to grow plants along the wires stretched between posts, against a wall or a fence (picture B below). It takes 3-4 years to establish the plant, but once it's done, Actinidia will continue to grow and bear fruit even for 50 years.

In the first growing season train a leading shoot. In January – February (do it before the vegetation period starts, otherwise it will bleed) trim it 3-5cm above the top of the supports (picture A2 and B2 below). In the second year choose a pair of the strongest lateral stems and train them to the sides tying them to a wire. In winter prune their tips leaving 8-12 buds on each of them (picture A3 and B3 below). In spring these buds will develop into permanent fruiting stems and will start yielding fruit in the following year. Again, they should be trained to the sides and pinched out at the tips in August to encourage the formation of numerous flower buds (picture A4 and B4 below). Pick berries in autumn (picture A5 below), and, in winter, cut back 30% to 70% of fruiting stems (picture AB 6 below), above the branching point from which new fruiting shoots will grow. Every year in summer and winter you should remove all side shoots growing from the trunk, and thin out excessive growth. Pruning helps control spreading and reduces vegetative vigour, promotes fruit growth and development, permits adequate air movement through the plant and opens up the inside of a shrub to maximize light penetration, all of which is essential for optimal fruit set, its flavour and quality.

 

Yielding fruit

Actinidias usually start bearing fruit in the fourth year after planting. When picked unripe, they will soften and ripen if kept together with fruit producing ethylene, e.g. with apples. It's best to put them in a cellophane bag and leave them for a few days at room temperature.

Berries are smooth-skinned, so they can be eaten without peeling. They can be eaten raw, added to cakes, jellies, salads and other dishes enriching summer and autumn meals, dried as grapes (they will resemble raisins), frozen and marinated. They are perfect for preparing wines, liqueurs, jams or marmalades.

Actinidia arguta fruits. Varieties from the left: 'Geneva', 'Weiki', 'Ken's Red', 'Jumbo' (photo Sz. Marczynski)

Actinidia fruit is very healthy. Being almost totally devoid of fat, low in sodium and rich in vitamins (E and C), potassium and other microelements, including zinc, it is a perfect supplement to a wholesome diet. The fruit of Actinidia arguta contains about 400 mg% of vitamin C, which is up to 4 times more than the vitamin C content of a lemon or an orange.