Our trees in Dakota County are subjected to a wide range of elements - wide temperature and humidity swings, sun exposure, strong winds and of course lots of hungry wildlife. Many trees, especially native trees, have evolved to survive all of the seasons in Minnesota. That said, we can take steps to prepare them for the winter season now. Newly planted trees in particular will benefit with some extra care to help them out this time of year.

Protect the roots

Cover the root zone of newly planted trees (within last 2-3 years) with 3-4 inches of shredded wood mulch to insulate the soil (snow cover on top will help insulate more). Keep mulch about 6 inches away from trunk - think “donut” not “volcano” of mulch - (this prevents unintended roots from forming and ultimately girdling the tree).

If the fall has been dry, as we’ve experienced recently in Minnesota, continue to water about once a week until the ground freezes. Read more about watering newly planted trees here. Look for cracks in the soil around new trees and fill any you find with soil.  This will help to keep cold air out over the winter.

Protect against damage from the sun and wind

For both deciduous and evergreen trees, the energy from the sun (even in the cold of winter) can warm trees up enough to stimulate activity. The tree then loses moisture above ground without being able to draw up new water through frozen soil by the roots so the tissues dry out and can be damaged. Any new growth is at risk of dying back when the tree cools off again. Trees planted without shelter from winter winds are even more susceptible to moisture loss.

For deciduous trees, protect the bark from winter sun and wind. A light-colored commercial tree wrap or plastic guard (not brown paper or black plastic) will reflect the sun and help to keep the bark at a more consistent temperature. Wrap newly planted trees for first two winters (and up to five winters if the species has thin bark such as a maple tree). Remove the wrap in the spring after the last frost so the tree can get back to healthy growing.  As the tree matures, the bark thickens and protects it better from sun scald.

This tree at Mendakota Park has white wrap around the trunk, a bag to water the tree’s roots slowly, and a stake with a loose twine attached to a guard around the trunk to prevent too much rocking in the wind without rubbing on the bark.  All of this is a great set up for success!

For evergreen trees, it is a very good idea to protect the tree from drying winds and winter sun.  Cover with trimmed evergreen boughs after the holiday season or wrap with burlap or a similar material.  Remember to leave the top open enough for air circulation and some indirect light penetration.

Try to minimize tree damage from wildlife

Hungry mice, rabbits, voles and deer can cause a lot of damage to trees and shrubs in your landscape over the winter!

Begin by reducing habitat in the fall - cut grasses and other vegetation short in late fall within two feet of young trees, and remove piles of brush in order to take away protective cover for rodents.   Don’t let them get comfortable in your yard when it’s cold outside.

Then, you can put up a physical barrier by creating a cylinder of 1/4 inch mesh hardware cloth around the tree trunk.  Keep the cylinder at least 6 inches away from the trunk (more if you want to enclose low hanging branches) to avoid causing damage.  Extend 2-3 inches under the soil if you are trying to keep mice away, 18 to 24 inches above the expected snow line in order to deter rabbits. 

If deer are hungry enough, it’s hard to keep them away.  As a protected species, the best strategies are removing comfortable areas to bed down and physical barriers.  Just like in the growing seasons, a high (8-12 ft) fence is generally needed to keep them away completely.  Repellents available at farm and garden stores can provide some help for deterring both deer and rabbits.

What about pruning and fertilizing trees in the fall?

With some exceptions, it is best to prune most trees at the end of winter while they are still dormant (with some exceptions for flowering and fruiting trees).  However, obviously broken or diseased limbs can be removed in the fall - especially once leaves have dropped and you can see the damage.  Read more about pruning here.

Lastly, be mindful of fertilizing trees, especially newly planted ones.  A burst of vigorous growth right before a freeze can be easily damaged, so it’s generally best to wait to apply until spring (sandy soils) or late in fall, once the tree is dormant (heavy soils).

It is a fine sight to see new buds sprouting on trees in the spring.  Help your trees along through the winter, especially those that are newly planted by:

-      Insulating their roots from cold and fluctuating temperatures with a good layer of mulch

-      Protecting bare deciduous trees and the foliage of evergreens from sun and wind damage

-      Making sure they get enough water through rain and supplemental irrigation up until the ground freezes.

-      Do what you can to help them defend against hungry critters

For more in depth information, refer to the University of Minnesota Extension website here:

https://extension.umn.edu/planting-and-growing-guides/protecting-trees-and-shrubs-winter

Photo credits: Sarah Heidtke (all)