CO-Horts

CO-Horts

Wednesday, January 7, 2015

When It's Cold Outside...

Posted by: Linda Langelo, Horticulture Agent, Golden Plains Area

....you can always add more layers to your clothing.  But not your plants, they are open to the elements.  When plants are exposed to high winds, fluctuating temperatures from warm to cold, there is water loss within the foliage.  This is called desiccation.  What is the best care for your plants? Here are some tips:
  • Knowledge of proper site selection for all your plants reduces stress and helps with winter injury, even with tender evergreens and perennials.
  • Providing protection for your plants by appropriately placing them nearby structures and other plantings.
  • Watering well before the ground freezes in late autumn hydrates plants giving them a good start.  When the ground freezes, the root system cannot uptake any water.
  • Fertilizing plants appropriately will help reduce plant stress.
  • Mulching around plants in the fall helps protect the root system by helping to maintain a steady soil temperature.  Do not mulch shallow rooted plants too deeply such as carpet bugle, thyme or blue fescue.  A mulch of about 2 inches will suffice.  Other plants can tolerate mulch up to 4 inches.  Too much mulch mitigates the oxygen in the soil available for the roots.  Shallow roots can get pushed out of the soil during the freezing and thawing of the soil over winter.  When mulching around trees, do not place mulch against the trunk which creates a condition of excess moisture.  This moisture attracts mold, fungus and insects to the bark.
  •  Using burlap as screening about 18 inches from the evergreen tree or shrub to help reduce the impact of winter winds.  However, if you live on the plains this option can be helpful for certain plants in your landscape plantings but impossible for any windbreak.  Rather pay attention to the first two tips mentioned above.
    Burlap protects evergreen plants from prevailing winds.
    (Photo from "sunny" Ohio; Alison O'Connor)
  • Winter mulches such as straw or evergreen boughs are good to use for perennials, bulbs, groundcovers and strawberry plantings.
  •  Pray for snow.  Snow provides insulation for plants.
How can you tell if your plants are desiccated?  Damage appears as browning at the tips and margins of needles and leaves of plants.  Some evergreens may exhibit yellowing or bronzing of their needles. The injury will appear on the side exposed to predominant winter winds.  
Browning and bronzing of evergreen needles.
(Photo courtesy of the University of Maryland)

Yellowing needles on evergreens from cold injury.
(Photo courtesy of the University of Maryland)
On some shrubs, freezing and thawing can turn to browning and blighting of the shrub.  Another sign of winter injury is blackened buds or buds that are dry and brown.  In trees, the bark can split due to the fluctuation in winter temperatures.  As in the picture below, courtesy of University of Maryland Extension, de-icing products can cause leaf scorch on plants by the sidewalk or roadway. 
Salt injury to evergreen foliage from de-icing products.
(Photo courtesy of the University of Maryland)
In spring do not rush to prune off those browned or bronzed needles of your evergreen plants.  Wait until the weather warms up which may be the middle of May to early June for some of us.  Don’t let the brown foliage fool you.  Check the stems and look for any new growth.    

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