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Plants don't always like winter. Unlike you and me, plants produce no heat. They cannot go inside, put on a pair of thermals or don their trusty overcoats. They are always at the mercy of Mother Nature.
When I wrote about winter kill last year in this column, it was pretty easy to assign the blame. Susceptible plants were severely damaged when the balmy fall temperatures suddenly dropped to below zero the week of Thanksgiving in 2010.
Thousands of plants eventually died during the spring and summer of 2011 and had to be removed. It was a costly weather problem that affected fruit trees, ornamental trees, shrubs and even herbaceous perennial plants.
This winter was kind to plants from a temperature standpoint. Few areas along the Wasatch Front saw the temperature drop below zero, and for the most part, temperatures were quite kind to growing plants.
Unfortunately, winter kill is not just about cold temperatures. Many other factors influence how your plants survive the winter.
This year the focus is on water in many forms, including snow. It also focuses on temperatures but on the other end of the scale or on how warm it has been this year.
Winter desiccation is a complex problem. It is not considered a direct result of low temperature, but in most cases it originates from the interaction of the water and temperature mentioned previously and also the wind.
While we usually associate desiccation with hot summer temperatures and lack of water, winter desiccation is another form of drought stress. This desiccation occurs when the water absorption by the roots cannot replace water lost through the foliage, buds or stems.
Transpiration and evaporation from the various plant parts increase under the following conditions: When temperatures rise above freezing particularly on bright, sunny, windy days, water loss increases.
It is much worse when the soils are frozen and the water absorption rate cannot replenish plant tissue moisture. Dehydration and eventual desiccation injury then damage the sensitive plants.
Signs of desiccation on plants with broadleaf winter foliage begin with the leaves curling or wilting and then progress to a browning of leaf margins. If the winter drought conditions are severe or persistent, the entire plant will turn brown and may eventually die.
Although people often worry about what snow is going to do to their plants, snow is not a problem unless the physical weight becomes heavy enough to break the plant. This year the problem is the lack of snow.
In years when the soil is covered with snow, plants will show a tell-tale snowline. Above the snow cover, the parts on which damage occurred are visible on the plants.
Desiccation injury varies with plant species, plant parts, soil moisture content, depth of frozen soil, snow cover and wind velocity. Desiccation is common on any plant with exposed foliage, including narrow- and broad-leaved evergreens.
The low relative humidity in Utah in the winter increases the water loss. In extreme cases, the leaves lose water while the ground is still frozen.
Among the plants that have been particularly hard hit are winter annuals, biennials and some perennials. Without the protection of a blanket of snow, the plants have dried out and in many cases the plants have dried out and died.
One technique used at Thanksgiving Point Gardens is covering the beds with a lightweight fabric. This is very effective in reducing winter desiccation and also encourages earlier growth on the covered plants.
Although it is too late now, winter watering might have helped some plants. Mulch is always helpful, although since it does not cover the plants, it does not totally protect them from desiccation. Providing wind protection can also help keep plants from drying out.
Winter kill takes many forms and can cause many different symptoms in your plants, bringing lots of problems. Learning how and what you can prevent is the key to protecting your plants.
Garden tips:
Utah State University will host its Master Gardener conference on March 25 in Utah County. There will be numerous tours, workshops and other learning experiences. The keynote speaker will be John Rader, co-founder of the Proven Winners Company — the world's most successful horticultural brand name. The conference is open to the public. Go to www.Extension.usu.edu/utah for more information.
Written by: Larry A. Sagers Horticulture Specialist Utah State University Extension Service
