Despite some recent snow, most of us have probably enjoyed not having to shovel
much or wear
ten layers of clothes until now this year. But our plants may be wondering what the
heck is going on. For that matter, most of our insects, mammals, and birds are
in a mild quandary, as well.
There are some definite reasons to have concern for our plants’ health when we have a warm, dry winter. The most problematic of these actually occur because of the lack of snow, or are directly linked to this phenomenon. The two items that are most likely to cause damage are the significant temperature variation and the desiccation potential.
Snow is nature’s Styrofoam®. For the most part, snow is at a
relatively constant temperature, just under the actual freezing point. There
will be some temperature fluctuation within a few inches of the snow surface,
but the fluctuation there is much less than the air temperature fluctuation.
This temperature constancy is an extremely positive thing for all the living
critters (plant or animal) that are found at or below the snow line.
Not having consistent snow cover causes temperature-related stress because of the excessive variability that occurs, and because the actual temperatures achieved can be significantly colder. Bare soil helped us achieve the 50+degree readings we had in early January, as soil absorbs light from the sun’s rays, whereas snow reflects sunlight. The energy in the sunlight is thus captured in the soil as heat, leading to much warmer temperatures on sunny days, especially at the soil line. The converse also occurs, and this is also a problem. Without snow’s insulation, the soil and perennial plants reach about the same cold temperatures overnight as the air reaches. Although our plants are hardy, they are not always designed to have their roots and/or crowns reach sub-zero temperatures, which can then cause serious injury or death.
Although it feels good to us and the non-hibernating critters, high
temperatures are not good for plants. If the temperatures are high enough and/or
long enough, the plants may be triggered to come out of dormancy. This would be
fine if it were to stay warm, but I’ll wager we are in for a few cold weeks
sometime this winter. Even if you do not see growth activities on your plants,
some of them may start sap flow or cellular activity on the south part of the
stem. This leads to severe damage when these areas re-freeze, and is the number
one reason that young trees are damaged and killed. The thinner the bark, the
more likely this is to occur. The other aspect to this occurrence is that the
plant wastes energy, which can lead to problems if we then have a late or
stressful spring. (Especially true in 2001-02, since we had some plants coming
out of dormancy once already in December.) Lastly, freeze/thaw cycles will also
increase the likelihood of crown heaving in perennials.
Besides the fact that we are not getting any moisture and the dryness that may cause this spring, having no snow also causes significantly drier conditions over the course of the winter. This will be most problematic for evergreens, but can affect any perennial. When there is no snow, the freeze/thaw action works to dry out bare soil. The more of this that occurs, the deeper the soil will dry out. As plant roots are primarily in the top six inches, lack of snow may cause severe desiccation of crowns and roots, leading to injury and death. The same idea can apply to stems of herbaceous perennials, especially those that are not fully adapted to our environment anyway.
Having healthy plants goes a long way to helping mediate potential damage,
but there are some things you can do now if you are concerned about possible
negative effects of no snow cover.
Simply put, the use of mulch is the answer to temperature and desiccation problems. If you have any perennial plantings that did not get mulched, find your rake and put leaves over them now. Watering is not the answer to desiccation, as this can cause ice sheeting if timed wrong.
Tree wraps or other such methods should be considered to help thin-barked trees not be affected by temperature fluctuation and freeze/thaw cycles.
Lastly, snow machines are NOT the answer, as they create sleet, now snow, which does not have the same insulation properties.
– Scott Reuss, UW-Extension Marinette Co.
