Frost-damaged plants

The time to clean up frost damaged plants arrived and many patient gardeners correctly waited. Those who hurried to prune the damaged parts out relied on chance and luck to make the proper cuts. Maybe they were lucky, maybe not.

Frost damage in plants results from the liquid inside individual cells freezing and forming ice crystals. The crystals then rupture the tough cell walls. When the cell walls open the fluid inside will not be contained so when the ice melts the fluids simply drain out causing the classic 'cooked spinach', wilted look.

Freeze damage is progressive within plants. The softest tissues like leaves and tender new shoots are hurt first. Tougher stem tissue and buds down from the tips withstand more damage but are not immune if the temperatures are lower and the duration is longer. Limp, dry and brouwn leaves damaged from frost stand out easily. Damage to stems and buds remains hidden for the most part.

Recognising how far down the stem damage has occurred takes a trained eye or luck. Tissues may appear undamaged but the damage hides latent until the spring flush of growth.

With this in mind the wise gardener waits until the new growth starts in the spring to find the point along the branch where the damage progressed. Once the spring growth happens the site along the branch where buds break out in new growth marks exactly where the damaged stopped.

One important thing to remember: the more severe the damage the longer it takes for the older buds to emerge. Young, undamaged buds break and grow early. Buds laying in older parts of the plant need more warmt and other stimuli to begin to grow.

When you find the exact point down the stem you can make the appropriate decision as to where to prune. Either cut about 1/2 inch above that bud if its going in the right direction or go further down and find another bud going in a better direction and cut it the same way.

This extra care and proper cutting helps the plant by directing its growth initially thus relieving later fix-up cuts that weaken a plant. Remember pruning is tough on plants. It removes leaves that make energy for the plant and the plant must expend energy to heal the wound.

So, fewer and better cuts cause the least damage to plants. A subject for more detail in next week's article

Written by Terry Mikel, College of Agriculture and Life Sciences, the University of Arizona, 602-470-8086.
Material originally appeared in Arizona Republic
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