Low temperatures leave plants in the cold

Source: David Trinklein, 573-882-9631; Michele Warmund, 573-882-9632

COLUMBIA, Mo. - Winter-hardy perennial flowers likely will survive April’s historic low temperatures across Missouri, said University of Missouri Extension horticulturist David Trinklein.

Their tender annual counterparts, however, may not be so lucky.

MU Extension horticulturists across the state answered numerous calls from concerned gardeners about freeze damage to their flowers and flowering shrubs as temperatures dropped into the 20s.

Perennials, even those in tight bud stage, likely will face minimal damage, Trinklein said. His callers included someone who feared losing a peony planting that has been in the family for more than 140 years.

Trinklein explained that peonies and other spring perennial favorites have survived other extreme weather events through the years and likely will survive this one.

Annual flowers that bloom only one season are more likely to fall victim to extreme temperatures. Annuals come in three classes: hardy, half-hardy and tender.

Hardy annuals, such as pansies, violas and snapdragons, will bounce back to brighten spring flower beds despite the cold weather.

Half-hardy plants, such as petunias, can tolerate light frosts but might not fare so well when temperatures drop to the 20s. Tender annuals usually die when plant tissue freezes, causing them to turn watery and mushy.

Potted plants face greater risk of damage than those planted in the ground and will survive better when brought inside the house or garage until temperatures rise and danger of frost passes.

In the vegetable garden, cabbages, broccoli, Brussels sprouts and kale likely will survive. Popular tender vegetables such as tomato and pepper are common casualties of cold.

Check the crown (growing points) of flowers and vegetables for damage, Trinklein said. Plants that still have a living growing point should recover but may be weakened. If this is the case, gardeners need to decide whether to replant or wait for plants to recover.

Many fruit trees and small fruit plants were likely damaged by the frost, but the extent of the damage depends on stage of bloom, said Michele Warmund, MU Extension horticulturist.

Pollinated fruits are less susceptible to frost injury, she said. Plants in low-lying areas face the most risk, so consider site selection.

Check flowering bushes and fruit trees by cutting a branch, taking it inside and putting it a container with cut ends of stems in water for a few days. Floral parts that are cold-injured will soon turn brown and wither, Warmund said.

After a freeze, do not apply nitrogen fertilizer to damaged fruit trees or bushes, she said. Additional nitrogen only creates more vegetative growth. Continue to water bushes and trees and watch for disease signs such as cankers. Warmund said it is important to closely monitor for signs of disease. If needed, follow MU Extension’s fruit spray schedule at extension.missouri.edu/g6010. For more information, see “Ice and Freeze Damage to Ornamental Trees: Implications and Remedies” at extension.missouri.edu/xr1.

Avoid future frost damage by covering plants with reusable row cover cloth and be patient when planting. “The best way to avoid frost damage is to plant at recommended times after the danger of frost passes,” Trinklein said.

For more information, visit USDA’s Plant Hardiness Zone Map at planthardiness.ars.usda.gov/PHZMWeb and MU’s Missouri Frost/Freeze Probabilities Guide at ipm.missouri.edu/frostfreezeguide.

Trinklein said that frost/freeze dates are averages to serve as a guide but are not fail-proof.