Even cold-hardy shrubs can occasionally suffer damage in freezing temperatures. If your region experiences an unusually cold winter or if your shrubs are forced to tolerate an early or late freeze, the damage can range from temporary and cosmetic to fatal. But careful plant selection, placement and care can minimize the damage and help your plants survive.
The easiest way to prevent cold damage to shrubs is to choose plants known to be cold hardy in your region. When planting broadleaf evergreens that are susceptible to damage, plant on the north, northeast or east side of your home to protect the plant from prevailing winds and harsh winter sun. This type of placement will also delay the spring growth of your shrub, helping it to survive a late frost.
Additionally, you can protect mature shrubs from severe weather by putting up a wind break. These can be easily made from a wood frame that covers two sides of the plant and a piece of burlap.
A thorough watering before a cold snap can have a protective effect, and mulching around the base of your shrubs helps to retain moisture and regulate the soil temperature.
Assessing the Damage
Although you may be tempted to prune dead-looking branches or even judge an entire shrub to be dead after a hard winter, it's best to wait until spring to assess the plant's true condition. This will require patience because a damaged shrub may be delayed in its spring growth.
Scraping a small spot on the branch with a knife can reveal its condition. If a green layer is evident beneath the surface, the branch should produce new growth soon. If no green is visible, the branch is likely dead.
Brown leaves are another symptom of cold damage. The leaves suffer damage when the shrub's ability to take in moisture through its roots is compromised by the frozen soil surrounding them. The problem is compounded by winter winds, which dry out the foliage. Damaged leaves can be removed by hand, but will most likely be shed naturally.
While the brown leaves can't be revived, your shrub may benefit from a mid-spring application of fertilizer. This will boost production of new leaves and help the shrub regain its healthy appearance.
Pruning Damaged Branches
If branches on your shrub fail to show signs of life after others are putting on spring growth and buds, pruning may be necessary. Trim the branch to within 1/4 inch of a healthy bud or flush with a healthy branch. Be sure to use clean, sharp loppers to make the cuts.
Damage to Flowering Shrubs
Sometimes unseasonably warm winter temperatures will confuse flowering shrubs and plants into putting on buds early. The real problem arises when temperatures then plummet back into normal winter ranges, damaging the buds and the flowers that may already have opened.
To gauge the damage to flower buds, cut open a forming bud. If it's green on the inside, it and most of its companions are probably healthy. If its black or brown on the inside, the bud is damaged and will not bloom.
Little can be done to correct this problem. Of some consolation is that most spring-flowering shrubs bud and bloom in waves, rather than all at one time. So even if you miss part of the bloom cycle for your plant, you'll likely catch a later show of buds and flowers.