June 28, 2017

Plant and Site Selection

James Luby and Emily E. Hoover with Bob Guthrie
Copyright Regents of the University of Minnesota. All rights reserved.

While winters may have moderated some during the past century the historical accounts demonstrate the importance of matching suitable plant material with local climatic conditions.  Native to the forests of eastern Asia, about 80 known species of Actinidia are known.  Two of these (A. arguta and A. polygama), can be grown in warmer portions of Minnesota (i.e., Twin Cities metro area inside the I-494/I-694 beltway and southeastern Minnesota).  A third kiwifruit species A. kolomikta is the most cold-hardy and can survive winter temperature minimums throughout the state.

Most kiwifruit plants are either male or female, but only the females produce berries while the males supply the pollen.  The smooth-skinned berries of the cold-hardy species are typically an emerald green, but with some A. arguta selections either the skin or flesh can appear reddish-purple, while some accessions of A. kolomikta may have a slight longitudinal ribbing.  With both species the berry shape can vary from round to elongate (which tends to be larger and generally higher-yielding).  Because it is the most cold-hardy species, A. kolomikta is a good choice to grow at suitable sites in Minnesota.  Suggested varieties include Krupnopladnaya, Sentyabraskaya, and A/O.  In a few years there may be some new hybrids available. A third species A. polygama can also be grown in southern Minnesota as a novelty, but unlike accessions from the other two species its fruit quality is lacking.  Some characteristics of all three species are summarized in the following table and depicted in Figure 1.

Actinidia Species A. kolomikta A. arguta A. polygama
Common Name Arctic Beauty Bower Berry Silver Vine
USDA Winter Hardiness Zone 3
Minnesota
Zone 4*
Southern Minnesota
Zone 4
Southern Minnesota
Taste and Flavor Generally good to excellent with a unique sweet-tart flavor and high-sugar content. Excellent sweet-tart (e.g., Geneva #3) to over fruity to bland. Green pepper to spicy flavor (unripe) to bland (ripe).
Berries Ripen Late July/early August to October (most varieties mid-August to mid-September). Mid-September to mid-October. Mid- to Late September.
Berry Size Small (2 to 7 grams). Wide range (5 to 20 grams). Small (3 to 10 grams).
Fruit Yield Up to 15 pounds. Up to 40+ pounds. Similar to A. kolomikta.
Plant Spacing 6 to 10 feet. 10 to 16 feet. 8 to 12 feet.
Attributes More compact growth habit (less labor), precocious, tri-color green-white-pink variegated foliage, ornamental prunings; very high in Vitamin C; small grape-sized berries can be dried to make “raisins.” Large grape-sized berries higher yields, spur-bearing habit of some accessions makes harvesting easier; attractive foliage with glossy green leaves and bright-red petioles.  Sun tolerant. Unique berry shape that turns from green to orange when ripe; bi-color green-white variegated foliage.
Shortcomings Fresh berries generally have a limited shelf life due to small size and high sugar content; rapidly emerges from dormancy in spring.
Does not grow well in full sun.
Vigorous growth habit requires more pruning. Flavor lacking; ripened orange berries attract robins.

* Some named A. arguta varieties are purported to be hardy to -35 F, though this claim has not been independently tested and verified.  “Issai” is a self-fertile A, arguta vine from Japan that is hardy to only -10 F (USDA Zone 6) and lacks sufficient cold hardiness for Minnesota winters.

 

Figure 1.  Kiwifruit berries.

Actinidia Species A. kolomikta A. arguta A. polygama
Common Name Arctic Beauty Bower Berry Silver Vine
  kiwi 1 kiwi2 kiwi3

Successful growing and fruit production can be achieved by emulating environmental conditions found in its native habitat.  Kiwifruit vines grow best under the following circumstances:

Site – Plant vines in a location where they will be shaded from afternoon sun and winter sun such as north or east of a tree line or building structure as these locations contribute to cooler and moister soil conditions favored by kiwifruit.  In the wild the trunks of kiwifruit vines are commonly shaded by trees, while the tops of the plant receive sunlight.  Trees also provide vines protection from strong winds and help protect tender shoots during the spring growth.  The cooler soil and air temperatures associated with these landscape positions delay bud break in the spring and help retain soil moisture during the growing season.  The selected location should also allow for air drainage (sloping ground) and avoid low-lying areas that can become frost pockets. 

Soil – Kiwifruit do best in a well-drained and aerated, moisture-retentive soil, rich in organic matter that is slightly acid to neutral.  Use a 4-inch thick woodchip mulch to retain moisture, regulate soil temperatures, control weeds, and encourage healthy root growth (Figure 2). 

Figure 2. Kiwifruit roots.
kiwi root

Compared with plants grown in bare soil, A. kolomikta grown under a thick layer of woodchips and leaf mulch tend to have a much more laterally extensive and denser root system containing a higher density of fine roots.  Many of these roots are distributed along the woodchip-soil interface and can extend several feet out from the trunk.