Apple trees grown in Minnesota have the same requirements as those
grown in other places: full sun, well-drained soil, a temperate
climate that permits dormancy and fulfills the buds chilling
requirement to break dormancy, and adequate soil moisture, whether
from rainfall or irrigation. In addition, apple trees benefit from
being planted on slopes, so that cold air can drain away downhill,
while warmer air floats back uphill.
In Minnesota, the importance of planting on a slope and not in
a low spot cannot be overemphasized. Cold air really does sink into
low spots, and apple trees must be sited so that the cold air can
drain away from them. Otherwise, flowers and tiny fruits can be
ruined by spring frosts. South-facing slopes are to be avoided,
because these sites warm up significantly earlier in spring, and
trees planted on these slopes will tend to flower much earlier than
those planted elsewhere. Early bloom is of no benefit. It increases
the chance that the flowers will be killed by frost and the crop
lost.
Rows should be oriented north-south wherever possible for best
light interception, leading to superior fruit quality. If ground
is so steep that north-south rows may lead to erosion problems,
the land may be too steep to be part of a commercial orchard planting.
Any orientation across a slope will require driving equipment across
the slope, which can be quite dangerous if the ground is steep.
Supplemental irrigation is particularly helpful in the first year
or two after planting. Normal Minnesota weather usually brings enough
rain during the growing season for trees to grow and produce good
fruit, but on sandy soils, irrigation for the life of the planting
may be essential. Even on moisture-retentive soils, irrigation can
be very useful during periodic summer dry spells.
Mulch of wood chips or similar materials, applied in the tree row,
can also help keep the trees root zones cool and moist. Although
wood chip mulch will not entirely control weeds, it will suppress
them. Growers whose trees are mulched can attend to the few weeds
within the rows on a more flexible schedule than growers who maintain
an herbicide strip in the rows. Wood chip mulch also affects soil
properties and leads to improved tree health and vigor, as well
as increased yields.
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