March 24, 2017

Training and Pruning

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

Kiwifruit vines need some sort of support for growth as the plants will twist around objects with a counter-clockwise growth habit and climb upward (Figure 3). Vines can be trained to a pole (e.g., Sturdy Stake) and then onto a trellis structure (T-bar or pergola) or for the backyard grower can be planted adjacent to a chain-link fence for support. For commercial production, a Pergola trellis structure offers several advantages over T-bar structures including:

  • Higher fruit production with a lower incidence of berry rub marks (a cork-like cosmetic blemish on the berry skin).
  • Easier harvest as the berries hang down from the overlying vegetative canopy.
  • More favorable soil conditions (cooler and moister) once the self-shading vegetative canopy is established.
  • Less weed growth (due to the shade).
  • Less suckering at the base of the trunk (also due to the shade).

Figure 3. Training.
training

Kiwifruit vines require support. Construct or purchase a durable trellis made of metal or wood, with wires or other supports extending horizontally. Wire fencing, supported by side posts, makes an adequate trellis.

Both T-bar and pergola trellis systems utilize high-tensile steel wire to support the vegetative canopy. The kiwifruit vine twists counterclockwise around objects that it can use for support. For ease of care and maximum fruit production, select a single, straight, vigorous shoot for the trunk that should be loosely secured to a vertical stake for support. For newly-planted vines training will take four to five years (as detailed below). For established plants with an established root system the training may take one to three years.

  • First Growing Season – transplant and allow the root system to become well-established for subsequent vegetative growth the following year. Most vegetative growth occurs early in late spring to early summer. Rapid growth terminates sooner for A. kolomikta compared to A. arguta.
  • Second Growing Season – look for a thick and vigorous shoot that is about the thickness of a pencil that will emerge near the base of the trunk one growth commences in the spring. Once this shoot starts to become woody in late June, prune away all other growth to leave this the single shoot. This will become the vine’s main trunk. Loosely secure the shoot to the support stake and allow it to grow for the remainder of the season, or until it reaches the overlying high-tensile steel wire and then pinch back to encourage the development of a secondary side shoot. This second shoot should be located about two thirds of the way up to trunk to the overlying support wire to form a “Y” configuration at the split. These will become the two main cordons (branches).
  • Third Growing Season – Cross the two cordons past one another so one cordon arm of the “Y” goes from the 2:00 position to 10:00, while the other cordon arm of the “Y” goes from 10:00 to 2:00. As growth progresses loosely wrap the two cordons around the support wire in a spiral fashion. Allow secondary shoots to emerge and grow out from the two cordons at uniformly spaced intervals of 8 to 12 inches. Continue to snip off any side shoots that arise lower down on the trunk.
  • Fourth Growing Season – Tie down the secondary shoots to the support wires. Specialized nylon clips keep the shoots in place and will keep them from shifting. These flower-bearing shoots are characterized by closely-spaced buds. These shoots will carry the fruit crop (for female plants) in the following year.
  • Fifth and Subsequent Seasons – Prune out old secondary canopy shoots and tie down new shoots that formed during the preceding growing season.

Much of the vegetative growth occurs during the spring and early summer. Left unchecked, vines can grow into a tangled impenetrable mess within a few seasons. In Minnesota there are three seasons when pruning can take place.

  • Mid- to Late Autumn – Once the soil begins to freeze. Major pruning should be undertaken at this time of year as the cuts on exposed wood will have the opportunity to dry out over the winter and reduce the potential for sap flow (bleeding) in the spring.
  • Late Winter – Prune while the soil remains frozen. Pruning cuts made at this time of year will be subject to profuse sap-flow bleeding. However, this can be averted by painting the cut areas with latex paint on a day when air temperatures are expected to remain above freezing for several hours so that the paint can dry.
  • Spring and Early Summer – Pruning at this time of year consists mostly of shearing, shaping, thinning and training to retain the desired plant architecture described above. Kiwifruit plants store starch in the woody tissue of the vine canopy. These starches are converted to sugar and translocated to the roots in the fall as day length shortens and nights become cool. As such, after mid-July extensive pruning should be delayed until the fall.