Hardening off fruit trees for proper dormancy

Fall has officially started according to the calendar, but fruit trees (and all trees in general) have been recognizing the signs that fall is coming for a long time.

Trees are receptive to the changes in day length as summer ends and fall starts.  They start to slow their growth and should have terminal buds set on most of their limbs by now.  You may still notice some active shoot growth, but the bulk of the limbs and shoots should be showing more mature, expanded leaves and a darker green look.  If you see a lot of fresh green growth by the end of September in the north, then you may have been fertilizing your trees too much.  Next year cut back on the fertilizer a little, and be careful not to fertilize too late in the season.

Trees respond to the cooler nights too.  This along with shorter day length triggers their desire to start going into dormancy for the winter.  As summer winds down and fall weather comes, frost during the nights and mornings will happen more often.  Don’t be worried about frost in particular as most fruit trees can tolerate a lot of frost and cold weather during the night.  However, if trees are excessively vigorous and have lots of light green growing points, then hard frosts may do some slight damage to these tender growing tips.

Unseasonable, early freezing events can cause young trees to suffer some damage though.  No matter where you live, if you have trees that are highly vigorous and growing too late into the late summer or early fall, an untimely early freeze event that lasts for several days may damage young trees.  So, this is another reason to try to make sure that trees are slowing down and not vigorously growing when October and November comes.  Thanksgiving is typically the day by which we want to have all of our nursery trees dug and in storage since by that time freezing temperatures or sudden dramatic changes in temperatures sometimes happen.  Young nursery trees are much more tender than the typical tree that is planted in the orchard.

In order to ensure that trees go into dormancy and harden off properly, the backyard orchardist should do these things as fall approaches in their area:

1. Reduce watering.  Usually late summer and fall rainfall comes more often and trees tend to need less water as fall approaches.  However, be careful of fall droughts.  If your late summer or fall is really dry, be sure to maintain adequate soil moisture to keep trees healthy.  Trees that suffer too much drought stress will show early leaf drop and be weaker going into the winter.
2. Do not fertilize at the end of summer or during early fall when trees still have leaves and are growing.  Too late fertilization can cause the trees to “wake up” and start to grow again.  You want trees to “fall asleep”, so that they can be fully asleep during the winter.  [One can fertilize in the winter when trees are fully dormant depending on your climate, but it is better to wait until late winter or early spring.]
3. Let the trees naturally stop growing and lose their leaves in the fall.  Don’t strip leaves off.  Some trees may actually retain some of their leaves which may stay on the trees until well into early winter.  Don’t be too concerned as long as the limbs and woody portions are well matured.  If there is green tissue still showing on the trees when freezing weather arrives, it may get damaged, but in most cases the trees will survive the winter in fine shape.
4.When leaves are off the trees, the time is good for fall applications of copper compounds to prevent leaf curl and bacterial diseases in peaches and nectarines and other stone fruits.  Apples and pears will benefit also as copper sprays will help to reduce fire blight potential for the coming spring.
5. Don’t prune in the fall.  There is still a lot of potential energy being transported down from the leaves into the root systems in the late fall and early winter.  If you have so many fruit trees that you need to do any pruning in the early winter, then wait as long as you can and start on the older apple and pear trees.  It is usually not recommended to prune any stone fruits in the fall or through the winter if possible.  Wait until spring to prune so that pruning cuts will heal up faster.
6. Work to deter “critter damage”.  Make sure that tree wraps are on the trunks so that rabbits, mice, and other critters don’t chew on the trunks.  Check often for deer browsing and hang soap or other “human smelling” substances in the trees to help deter them.  If buck deer are prevalent in your area, then caging your trees for the winter might help protect them from rubbing their horns on the trunks and limbs.
Grandpa has found that most backyard growers don’t encourage enough vigor in their newly planted trees, so going into proper dormancy will not be an issue for most growers, unless they are the type of gardener who really pushes for growth.