The term “blackberry winter” might make you think of enjoying blackberry cobbler on a cold winter’s day. What it really refers to is a cold spell that happens in the spring when blackberries are flowering. And this weekend in Western North Carolina, as the blackberries come into full bloom and forecasted temperatures drop into the low 30’s, we will experience a “blackberry winter.”  Many of our plants will be affected by the cold temperatures and frost, not just blackberries.

Mitigating factors

Damage to plants can vary and will depend on several factors.

• Cloud cover and light winds can moderate temperatures and reduce the chance of frost settling on plants.
• Developmental stage of the plant is also key. Plants sprouting tender new growth of foliage, flower, and fruit are highly susceptible to damage. Plants fresh from the greenhouse and not acclimated to the outdoors may also be hurt.
• Garden location affects the level of damage or protection a plant receives. The climate of a garden site, often called a microclimate, is affected by the lay of the land, nearby structures, and windbreaks. Cold air and frost pockets settle near the bottom of a slope. Structures and windbreaks can provide warmth and protection.

Plant susceptibility

Cold temperatures and frost will impact plants in the following ways:

• Fruit trees vary in their hardiness according to their stage of flowering. If fruit trees have flowered and set their fruit, they should be safe from a light frost. Lower temperatures that damage some fruit is simply an act of nature that thins the fruit, giving the remaining fruit space to grow to full size.
• Small fruits that are in flower, like blueberries, strawberries, blackberries, and raspberries, will be susceptible to damage and ultimately may not set fruit.
• Warm season vegetables, such as peppers, tomatoes, and cucumbers, and all tender annual flowers will be damaged if temperatures drop into the low 30’s.
• Cool season vegetables, such as early peas, greens, beets, carrots, onions, broccoli, and cabbage, are all considered cold hardy and can withstand freezing temperatures with no notable damage.
• New growth on ornamental trees and shrubs, such as Japanese maples (already hit once this season), hydrangeas, and roses, can be damaged. As will the flowers of azaleas and rhododendrons that are right now in their full glory. Flowers still in tight bud should be okay.

Protection 

If possible, cover your plants as the temperature drops.

• Lightweight fabrics, such as floating row covers, frost blankets, or other polyspun materials, work well for frost protection. If you do not have this type of fabric, cotton sheeting, lightweight blankets, or other insulating materials can be used. Double layers provide more protection than single layers. Make sure covers extend down to the ground and are anchored by bricks, stones, or landscape staples. This protects the plant from blowing wind and secures openings where heat can escape.
• Plastic coverings or tarps can work, but because of weight should be used with caution on more delicate plants. Keep plant foliage from coming in direct contact with the plastic since this can cause the leaves to freeze.
• Buckets, containers, or other devices are an easy way to cover individual vegetable plants and provide frost protection as long as the plant can be adequately covered without damage.

Always, always, always be sure to uncover plants as soon as the temperature begins to rise the next day. This is especially important when using clear plastic. The chance of plants overheating and burning from bright sun and warming temperatures creates another problem entirely.

It is helpful to point out that the Master Gardener℠ volunteers of Buncombe County recommendation is to delay planting warm-season vegetables and flowering annuals until Mother’s Day . . . which is this coming weekend!

The blackberry winter experience

Given our “stay home stay safe” time this year, many gardens are well on their way to full growth and beauty. Although it is worth making the effort to protect plants from freezing temperatures, protecting all your plants may not be possible. Do the best you can. Blackberry winters will always come and go. Some plants will die, some will be damaged, and many will survive. This is part of every gardener’s experience here in Western North Carolina. Be resilient, plant again, and take pleasure in the learning.