Winter’s lack of water and frigid temperatures are challenges that are overcome by going into
hibernation (dormancy).
Before dormancy begins, trees take up extra water and stock their cells. Water is removed and stored
between the tree cells to keep them from freezing and dying during extreme cold temperatures. The
water inside the tree does freeze, but first gives off small burst of heat, just enough to keep the tree
cells alive. To further adapt to the cold, trees transform starch to sugar inside the cells.
Winter Challenges
• Early cold spells can damage plant tissues that have not had the chance to harden off for the
winter.
• Dry winds and winter sun can dry out and burn conifer needles.
• Extreme winds. Trunk and branch breakage.
• Frozen soil – The effect of frozen soil prevents water take-up to replace the moisture lost from
evaporations and transpiration. Drying winds desiccates trees and forces them out of
dormancy. The soil and roots are frozen not allowing the tree to get water to the extremities
causing the affected twigs and branches to die back.
• Extreme temperature changes causing damaging freeze thaw cycles. Mid-winter thaws warm
temperatures and drying chinook winds, can trick trees out of dormancy. Allowing sap to run
and new growth to happen. As temperatures return to winter norms new growth is frozen and
dies back.
Winter Die Off
• Occurs when parts of the tree freezes and dies back during the winter.
• Signs are
o Dry brittle wood that breaks easily
o Large amounts of fungus.
o Sores or cankers visible on branches.
Sun Scald or Winter burn
• Can be caused by winds OR reflection off snow.
• More common to south facing trees and shrubs.
• Clear cold sunny days. The light reflected off the snow warms the tree enough to allow a
slight thaw in the tree tissues. The sun sets and the tissues are frozen again. Eventually this
freeze/thaw cycle will cause a crack in the bark, exposing the inner layers and damaging the
tree.
Warm Temperatures in the Fall
• Warm temperatures in the fall may trick the tree into not preparing for winter. This delay will
make the tree susceptible to getting burned by the cold and not surviving the winter as the
dormancy process was not completed.
Cold Injury
• Cold injury usually occurs min winter, caused by an extreme drop in temperatures going into
the evening after a warm sunny day.
• Foliage that faces the sun on sunny days, can begin to transpire. The ground is still frozen
preventing the tree from taking up water, causing the foliage to dry and brown.
Helpful Hints
• Water. Water throughout the fall until ground freezes. Water eep to reach the root
zone.
• Use mulch. This acts as an insulator for the soil and reduces the effects of the
freeze/thaw cycles and drying winds. It also mitigates moisture loss during spring and
summer.
• Do not fertilize in late summer. Fertilizing in late summer causes a late growth spurt and
prevents the tree from starting dormancy.
• Trim dead branches. Trimming dead branches will promote growth in the healthier parts
of the tree during the growing season.
• Snow removal. Be aware of where you are piling the snow. Do not create snow banks
that will cause light reflection on tree trunks and evergreen foliage.
• Watering in winter. Water in winter if warm and ground is exposed