Freezing temps have passed

What damage to expect on plants, trees and shrubberies

By John Fulton         

[April 09, 2007]  ^"Wait and see" is the best advice concerning perennials subjected to the freezing temperatures of the last week. Temperatures below 25 degrees are generally regarded as harmful to budding and blooming plants. Temperatures of about 18 degrees are more damaging.

Flowers such as daffodils and tulips definitely took a hit. The blooms exposed froze, and stems and flower buds froze. What's the outlook for the plants? Existing foliage, and new growth, should provide plenty of foliage for the bulbs to store energy to go through the winter. The bulbs are well protected below the soil, and there should be no damage to bulbs planted at the proper depth.

Trees and shrubs recommended for our hardiness zone (5b) should fare well. They've been through this before, and probably will again. Plants normally planted in more southern zones may suffer more significant damage, while those normally planted farther north should suffer less. A lot of the damage is dependent on the actual stage of development.

Many of our flowering trees and shrubs that show early blooms, such as dogwoods and redbuds, will lose most if not all blooms. Even early trees will show significant damage to the exposed fruit and leaf tissue and buds. Maple trees in particular will probably show some frost cracks, and these will be most significant on smaller diameter trees. Frost cracks are long, vertical cracks in the main trunks of the trees. They heal easily and don't cause long-term damage to trees. They are very visible and cause concern when they are discovered. The damage is similar to a jug of water freezing. The trunk is full of sap, and the freeze causes the sap to expand. This causes the large crack.

There will be some very tough-looking foliage on some trees, with many black or brown tips or margins, similar to anthracnose damage. Later trees, such as oaks, will show little or no effects, due to the delayed swelling of the buds.

Some plants are marginally hardy in our area. They will probably show some dieback or death. Boxwoods traditionally are severely affected by cold snaps at abnormal times. But once again, wait and see. Abnormal pruning patterns may also cause more severe injury.

In summary, healthy perennials will probably look somewhat rough this year. There will probably be more damage to flower and fruit buds than to leaf buds, but leaves may be misshapen or have dead portions. If leaves were severely affected, a new set of leaf buds will come out later. Of course this will take some stored energy from the trees' storage. The best thing we can do is the simplest. Water when it is dry, and make sure to fertilize at the right time. The blanket recommendation is to use a "lawn rate" over everything. This would be 10 pounds of 10-10-10 or 8 pounds of 12-12-12 or 13-13-13 per 1,000 square feet. It is best to fertilize everything about the first week of May.

It's amazing what can happen with very warm temperatures, followed by a quick cold snap of the degree we experienced. Wait and see. That's the best advice for now.

[Text from file received from John Fulton, University of Illinois Extension, Logan County Unit]