BY Sarah Busdon
Preventing frost damage as cooler weather approaches will not only extend your gardening season but will also protect your plants.
Frost injures plants by causing ice crystals to form in plant cells. This makes water unavailable to plant tissues and disrupts the movement of fluids. Frost-damaged leaves appear water-soaked, shrivel and turn dark brown or black.
Plants are classified according to the minimum temperatures they normally tolerate. “Hardy” plants tolerate some amount of short-term freezing while “tender” plants are killed or injured by freezing temperatures.
Site selection can help prevent frost damage. Elevation, surface reflectivity, soil properties, canopy cover and proximity of structures or plants can all affect heat radiation within your landscape. Avoid planting tender species in open, exposed areas or in low spots where cold air settles. Put them near a south- or west-facing wall, which absorbs heat during the day and radiates it at night. Fences, boulders and shrubs also can serve a protective function for nearby plantings.
Here are a few precautionary measures you can take:
• Bed sheets, drop cloths, blankets and plastic sheets make suitable covers for vulnerable plants. Use stakes to keep material from touching foliage.
• Remove the coverings when temperatures rise the next day.
• For a short cold period, low plantings can be covered with mulch, such as straw or leaves. Remove once the danger of frost has passed.
• Be creative – cover plants with empty milk jugs.
• Spray an anti-transpirant, available at your local nursery, on the foliage of cold-sensitive plants to seal in moisture.
• Cluster container plants close together and, if possible, in a sheltered spot close to the house.
Plants can be very resilient. If you see signs of frost damage, don’t prune off the affected parts or dig up the plant immediately. Wait until the weather warms up in April to see whether new leaves sprout. You may see healthy new growth at the base of the plant, at which point you can prune out the damaged parts. If no regrowth is noted, remove the dead specimen and replace it with a more cold-tolerant species.
Sarah Busdon is an administrative assistant with University of Idaho’s Blaine County Extension office. For more information, visit extension.uidaho.edu/blaine or call (208) 788-5585.