For nurserymen spring cold like we are experiencing or about to experience (it is snowing so hard I can not see the greenhouses as I type) can spell disaster. The most frustrating part of trying to advise folks right now is that we do not know how cold it will be in their nursery nor do we know exactly how much cold it will take to severely damage the vast variety of crops we grow.

I was in Piedmont nurseries last week that had six inches of new growth on plants that seemed to be just breaking bud a week before. It was 85F, 90F or warmer in these nurseries last week and plants were just doing what they are supposed to when they have been through winter, have plenty of water and fertilizer and the temperature gets warm. They were growing rapidly.

Temperatures here are supposed to be in the 20's F. for the next two mornings. What should you do? If temperatures are not going to be in the 20's where you are, be happy. If they are, get busy.

First, please understand that normally very cold hardy plants WILL BE DAMAGED by frost and temperatures in the 20's F. when they are actively growing. Evidence of this is the number of germinating Colorado blue spruce and sugar maple seedlings that are killed by frost every spring if not protected or all those 'Mountain Fire' Pieris japonica that have the new spring growth killed by frost when new vegetative growth precedes a 25 F. morning.

Flower petal tissue is probably the most susceptible to cold injury right now along with the tender new vegetative growth on a wide variety of plants. Temperatures will not be cold long enough to do serious damage to the roots of most normally hardy plants.

For container growers, do everything you can to physically protect cold susceptible plants. Pulling a frost blanket (with support of some sort so the frost blanket does not break the new growth off your plants), recovering overwintering houses temporarily (which is what we have done at the research station) or just moving plants under cover will all help. If the temperature gets too low into the 20's and you do not protect, you will lose flowers and the new vegetative growth. For retailers, this usually means plants are unsalable. For wholesalers, it means you will need to wait for a new flush of growth and need to do some pruning before plants are salable.

Icing plants down, i.e., turning on the irrigation before the temperature drops to freezing then continuing to run the irrigation until the ice melts, is rarely a good option under conditions like we will experience where the temperatures drop into the low 20's but may be an option if the temperature drops to freezing just before sunrise. Where temperatures are to be in the low 20's, the irrigation will probably need to be running by 9 PM and run until 10 AM the next day. That's a lot of water and a lot of heavy ice. Breakage can be a real problem.

So . . . bottom line . . . protect susceptible plants if the temperatures are likely to be in the 20's F. Field grown plants may lose some flowers but most I have visited will probably be okay or just experience minimal loss of new growth. Increased summer pruning and an increased possibility of pests are the only real problems. For container growers, retailers, rewholesale yards and similar parts of the green industry, do what you can to protect the plants.

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North Carolina State University