Freeze Damage Potential on Rhubarb and Other Fruits; on Landscape Perennials
By John Fulton

Send a link to a friend  Share

[April 07, 2016]  Freeze Damage Potential on Rhubarb and Other Fruits - A little bit of warm weather spurred some growth in many of our perennials. Then a hard freeze comes along and some of our plants may need some special care.

Of course we can expect some fruit reduction in cases where severe frost or freezing catch trees in the tender bloom and early fruit set stages. Book figures are about a 10% reduction in apples at full bloom with a temperature of 28 degrees. Peaches and apricots in early fruit set at similar temperatures will see about a 25% fruit reduction. An additional decrease in temperature to about 26 degrees magnifies the losses. Of course this isn’t always bad. Many have been complaining the past couple of years about too much fruit and broken branches.

Of bigger concern is rhubarb. A hard freeze can actually damage leaf cells enough to release a toxin back into the leaf stalks. The leaves are always toxic on rhubarb, and if damaged enough to wilt or have black or brown along the edges, the toxin is almost certainly released. The solution is rather simple, at least this early in the game. Pull the stalks with the damaged leaves, and you get to start over with the regrowth. It may happen again as the plants have more growth, but at least now we are early enough we don’t feel quite so bad about starting at ground level again.

For those who got some potatoes out, if foliage is damaged enough to wilt, it is probably best to cut tops back to ground level and allow regrowth. Rotting back into the tubers causes more problems later on.

Freeze Damage on Landscape Perennials

“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. We were right in the 25 degree range overnight.

Exposed 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. Also, remember many of our perennials are sheltered by the house or other structures, so damage may not even be noticeable.

Trees and shrubs recommended for our hardiness zone 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 further north should suffer less. A lot of the damage is dependent on the actual stage of development.

[to top of second column]

 Many of our flowering trees and shrubs that show early blooms, such as dogwoods, Bradford pear, 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 often 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. We probably did not have sustained freezing temperatures for a long enough period to affect large diameter trees.

There will be some very tough looking foliage on some trees with many black or brown tips or margins, similar to anthracnose damage, as small leaves are forming on some trees. 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 eight pounds of 12-12-12 or 13-13-13 per 1000 square feet. It is best to fertilize everything about the first week of May. Wait and see. That’s the best advice for now.



Back to top