We received this fax today from K-State’s Horticulture Department. Given the number of phone calls, emails and client inquiries about the potential damage to plants with the unseasonably cold weather (yes, that was snow we got on Friday night…), we wanted to pass it on. If you have any questions, please email Mitch, Brent, Jon or myself at the office for clarification.

FOR IMMEDIATE RELEASE

Date: April 10, 2007

Contact: Dennis L. Patton, County Extension Agent, Horticulture (913) 715-7000

Dealing with the aftermath of the hard freeze on landscape plants

Olathe, Kan. – The early April freeze has taken a toll on local landscapes. Plants that were awash in spring color have no lost their pastel hue and, in many cases, turned a dull brown, white, or translucent green. Care should be taken before attempting to correct the freeze injury.

The best advice for the short term is to do nothing. Give the plants at least two weeks to recover. Pruning or removing leaves or branches may result in more long-term injury than just living with the current effects. This time period, depending on the temperatures, should give the plant time to develop secondary buds that will grow and result in a re-leafing of the plant. For each of the following groupings of plants, follow these guidelines in addition to the waiting period.

PERENNIALS

Perennial garden flowers such as iris, hosta, daylilies and other are in poor condition. Many of the leaves have turned white or dull tan as a result of the freeze damage. Perennial leaves that have completely discolored can be individually removed to help tidy up the plant. One word of caution; pars of damaged foliage that still have some healthy green tissue should not be removed. Some functioning plant tissue is better than none at all for long term health. Even though the plant may not look the best, this foliage will help generate energy for the plant. Hostas may be the best example of this. A few years ago a hail storm riddled the leaves. Some gardeners cute the plants back while others left the damaged foliage. A year later the plants that were not cut back were bigger and stronger.

For peonies, the early season varieties may have been damaged. Again, just wait before doing anything. If, after the weather warms, the buds are dark, sunken, or shriveled, carefully remove the bud down to the first leaf, being careful no to remove and energy-producing foliage.

TREES and SHRUBS

Trees and shrubs were also damaged. Succulent growth has blackened or turned brown. Do not prune or remove any branches or twigs until the new growth is visible. Woody plants will develop secondary buds that will go on and put out new growth. The development of this tissue may take a couple weeks or more, depending on the plant and weather conditions. Hastily pruning now may remove those secondary buds before they have a chance to fully develop. Once new growth has developed and is growing strongly, pruning can be done to remove any dead twigs. Even without pruning, the fine limbs that froze will eventually fall from the plant over time.

Plants that produce blooms on new wood should not be affects by the cold temperatures. The lilac bloom this spring may be sporadic. The first flush of shrub roses that usually occurs in late May could be delayed or less spectacular than usual.

Trees and shrubs may have incurred more damage than just twig dieback. There is the potential that the hard freeze may have also damaged bark tissue. This type of damage is much more severe, as it would affect the vascular system of the plants. If damage to the cambium bark layer did occur, then the main trunk or branches may develop dark sunken lesions later this growing season. This damage would restrict the movement of water up into the plant and the translocation of nutrients into the root system. As a result the plant will be weakened, possible resulting in a decline in growth or limb dieback which will make the pant more susceptible to borer injury.

FRUIT TREES

Unfortunately, the fruit trees were hit particularly hard. Most fruit trees bloom early and the freeze could have killed the vast majority of the flower buds. The more open or colorful the bud, the greater the chances it was lost. The tighter the bud, the more natural defense the tree had against the frost. Again, the greater concern is the potential damage to the cambium bark.

What can be done now? A light fertilization of perennial gardens now may help regenerate new foliage, depending on the plant. Established treed and shrubs will not benefit greatly from fertilization. Younger trees may benefit from an application of fertilizer. Watering throughout the summer of 2007 to stave off drought conditions may be the best remedy for the freeze injury. Adding additional stress the plants will only compound the injury.

For information about individual plant damage or the general care of your landscape plants contact Johnson County K-State Research and Extension Horticulture Hotline at (913) 715-7050 or e-mail garden.help@jocogov.org.

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