By: Kelly Feehan,
Extension Educator
We’ve had some cold temperatures and windy days. Without snow cover to act as insulation, it is a good idea to check winter protection on tender perennials like some roses, chrysanthemums and strawberries. Or add mulch if needed.
For tender plants mulched in late fall for winter protection, check to see the mulch is deep enough and has not blown off plants. Mulch layers should be about six to eight inches deep and not matted down. If necessary, rake mulch back into place and add additional mulch. If matted, fluff it up with a rake.
Plants considered tender in Nebraska are those listed for cold hardiness zones 5a or 6a, especially zone 6a or 6b. Most zone 5a and 5b plants are hardy but the location planted in and care provided can affect hardiness. For example, drought stressed plants or plants fertilized in late summer or early fall may be more likely to sustain winter injury.
Some gardeners experiment and try plants just outside our hardiness zone. While this can be interesting with perennials, it is risky with trees or shrubs which are more expensive and take longer to grow back to size if winter killed. Northeast Nebraska is in hardiness zones 5a and 5b. Plants hardy to this number or lower are best planted.
Be careful about selecting plants hardy to zones 2 or 3. These are the cold hardiness zones for North Dakota. Plants hardy there may struggle with Nebraska’s hot summer temperatures. Plants need to be both cold and heat hardy to the area they are planted to.
As mentioned above, some roses, chrysanthemums and strawberries are the most common plants grown we recommend be winter mulched. When slightly tender plants are selected, they can be protected by covering plants with a coarse mulch close to or after the soil has frozen in late fall or early winter.
Another winter risk is winter desiccation or burn. This is drying out of tissues exposed to cold temperatures, wind, and winter sun. This type of injury is much more likely to occur in an open winter with little snow. And any plant can be injured, hardy or not.
If concerned about winter burn of exposed plants, a six-inch layer of mulch will help. Some examples are wood chips, large leaves, and straw. The coarser the mulch, the deeper it should be. To prevent mulch from blowing away, place it in a chicken wire cage or weight it down with branches.
I was recently asked about placing a tarp over straw mulch to prevent it from blowing away. The concern with a tarp is lack of ventilation. And if the tarp is a dark color, it will absorb heat from the sun and dry out plants beneath it or cause them to begin to break dormancy too soon.
For the same reason, it is a good idea to check on roses or other plants protected by rose cones, especially on warmer winter days. The cones may need to be ventilated to prevent heat build-up inside the cone, which can dry plant tissues and lead to winter kill.
Ventilate the rose or other plant by cutting the top off the rose cone. At night and on cold days, place the top on the cone and weight it with a rock. On above average temperature days, remove the top to ventilate the plant inside.
Besides tender plants, winter mulch is recommended for young plants, especially those planted last fall. In this case, mulch maintains a uniform soil temperature to prevent freezing and thawing that can damage roots or heave young plants out of soil, exposing roots to drying and cold temperatures.