October 23, 2017

Irrigation, Fertilization, Winter Protection and Harvest

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

Irrigation

While the annual temperature regime in Minnesota is similar to that of northeast China, the precipitation regime is not. Typical Minnesota summers are characterized by a generally dry climate during the mid- and late-summer, whereas eastern Asia usually receives much more precipitation (due to the summer monsoons) during this same time period. As such, supplemental irrigation or watering will be needed during most Minnesota summers as drought-stressed plants are prone to premature berry drop (for A. kolomikta), result in a reduction of fruit size and crop yields, and make plants much more susceptible to winter cold injury.

Fertilization

Kiwifruit benefit from the application of fertilizer containing nitrogen (such as ammonium nitrate) and potassium in the chloride form (muriate of potash = potassium chloride). Light applications should be broadcast around the trunk area from the spring (once frost is out) into early July. Most Minnesota soils have adequate phosphorous for plant growth; however, if a soil test (see more information at http://soiltest.cfans.umn.edu/) shows a lack of phosphorus, be sure to use a complete fertilizer. Woodchip mulch will generally not tie up nitrogen unless the woodchips were incorporated into the soil during planting.

Winter Protection

Cottontail rabbits can cause extensive damage to kiwifruit plants during the fall and winter months (particularly after the first snowfall when other food becomes scarce) and may completely girdle the vine’s trunk. Secure fencing of adequate height for anticipated snow depths protects the plants. A shade barrier may also be needed on the south and southwest sides of the vine’s trunk if insufficient shade is available. The dark-colored bark readily absorbs and accumulates daytime heat especially in late winter when the exposed trunks can be exposed to the lethal combination of direct sunshine and snow-reflected radiation. This sunscald damage can be avoided by using spiral wraps (Figure 3) or by driving two wooden stakes into the ground during the fall and then slipping a burlap sack or old pillow case over the two stakes to serve as a shade barrier.

Figure 3. Trunk wraps.
wraps

White Spiral wraps help protect trunks from sunscald damage during the winter months.

Harvest

When ripe berries change both their appearance and firmness going from hard, opaque and glossy to soft, slightly translucent, and soft when gently squeezed. Once the berries start to ripen, the remainder of the berries can be picked.