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Preparing Fruit Trees for Winter for Zones 3-7
The beautiful weather in middle fall may not allow the trees to go into dormancy on a regular schedule. If an abrupt plummet of sub-zero temperatures occur fruit trees can incur damage due to the moisture in their branches freezing.
As long as we don’t have a sudden freezing event, and the trees are allowed to go into dormancy gradually, we have a better chance of healthy trees next year.
Most all deciduous fruit trees do not need protection from the winter cold. However, these trees can be killed or damaged if they are not sufficiently hardened with enough pre-conditioning cold temperatures to halt their growth.
The length of time fruit trees are exposed to sub-freezing temperatures is also significant. Exposure to sub-freezing temperatures for more than 24 to 36 hours can harm them if not fully hardened for winter. But, if the temperature moderates to above freezing prior to this time, damage is often avoided.
Deciduous fruit trees increase in hardiness as they age. Most likely due to their denser canopies which deal with the cold better as they trap some heat.
Generally, when freeze injury occurs, damage is inflicted mostly to cell membranes by freezing and thawing. The least cold-hardy tissues of fruit trees are new buds and new growth. The more cold-hardy part of the tree is the mature wood of major branches and the trunk.
Trees that are gradually exposed to cooler temperatures, a process called hardening occurs, and trees become more tolerant to freezing temperatures. This conditioning, by gradual cold, are less likely to be damaged by cold. Chilly but above freezing nights, mid to upper 30s and 40s are ideal temperatures for conditioning trees to be cold tolerant. Severe freezes taking place when only mild weather has occurred previously are more likely to cause significant damage.
The best way to lessen cold damage in fruit trees is to maintain healthy trees. Cultural practices that tend to induce and maintain dormancy in winter should be used. These methods include no late summer or fall fertilization or pruning. Vigorous trees may recover from cold injury. Weak trees that are showing disease, insect damage, or nutritional deficiencies are the ones most severely damaged and are the slowest to recover after freezes.
A few steps to consider for preparation of winter cold;
Covering the lower trunks of trees using tree wraps of bubble wrap, foam rubber or Styrofoam will help prevent cold damage to the trunk. This must be done before the first killing freeze and can be left on through the winter. Although tree tops may still be lost during freezes, a tree can recover if its trunk and root system are intact.
If the weather has been dry, several days in advance of a cold front the soil beneath fruit trees can be irrigated. Good soil moisture acts as a cold buffer, and trees that are drought stressed may experience more cold damage. This must be done well in advance of the freeze. If this is done at the time the front arrives, evaporation may occur and result in colder temperatures near the tree.
Pruning should be done in spring and early summer to allow tree growth to mature before winter. Do not prune in the late summer or fall.
Fertilizer should be applied to trees from late winter to late spring. A complete organic fertilizer at the rate of two to four pounds per year of tree age may be used. Spread the fertilizer around the edge of the branches in the area of the feeder roots. Late summer or fall applications of fertilizer should be avoided as they can reduce the hardiness.
Oil sprays used to control insects and mites decrease cold tolerance and should not be used later than August 15.