Pruning Freeze Damaged Plants

The intense, freezing temperatures this winter caused considerable damage to many Pinal County plants and some of you are wondering how to prune out the damage.

Before we get into that, let’s review some basic facts about citrus that will help us make good decisions when it comes time to prune.  Unlike deciduous fruit trees such as peaches, apricots and apples, it is important to remember that citrus do not need to be pruned every year to ensure good fruit production and tree health.  Neither do we need to prune citrus to reduce fruit load like we do in the deciduous fruit varieties.  Citrus branches are strong and flexible and can carry a heavy load without breaking.

Another reason to avoid going hog wild with the pruning shears is loss of production. Citrus fruit is borne on the tender tips of branches out near the outside edge of the tree.  Removal of these tips by shaving or pruning significantly reduces the ability of the tree to produce fruit each year.  Removal of the bottom tier of branches to give the tree a ‘typical’ tree look can eliminate up to a third of the total fruit production capability of these plants.

The last reason to not prune citrus is plant health.  Citrus trees have tender bark that is easily sunburned when sunlight strikes unprotected wood.  Usually the heavy canopy of leaves shades and protects the trunk and major branches of the tree, but when branches are removed or foliage is shaved from the tree, the bark is often exposed to the sunlight.  Sunburned bark can often be found on the southwest side of citrus tree trunks whose bottom skirt of branches has been removed.

What about the lower branches that drag fruit on the ground?  That is a good reason to prune out low hanging wood but if you want a highly productive, healthy tree, remember to only take off those branches that are causing the problem and no more.

Okay, let’s talk freeze damage.  Dead and dying wood is showing up in a number of different plants this year.  Besides citrus, other plants showing significant freeze damage include bougainvillea, ‘petite’ oleanders, palm trees and Queens wreath vines.  In some cases, the entire plant has died.  In other cases, damage is minimal.

Severity of damage is dependent upon many factors.  The age of the plant, the specific weather conditions around the plant, and its genetic make up play a key role in whether a plant will be damaged or not.

Before doing any cutting, we need to be able to distinguish between dead leaves and dead wood.  Just because a tree is completely defoliated from the cold weather and looks ‘dead’ does not necessarily mean that the twigs and branches of the plant have been killed.  It fact, they may not be damaged at all.  For these reasons, it is essential that before you cut, you need to find out what is dead and what may still be alive.  Be careful here because, particularly in citrus, you do not want to prune off any more wood than is necessary.

We tell the difference between dead wood and live wood by doing the scratch test.  This is done by scratching the surface of the bark gently with a thumbnail or a knife.  If the wood underneath the bark is green and moist, it is still alive.  If it is hard, dry and brown underneath, it is dead.  While this sounds easy, and most of the year it is, the time right after the damage occurs is a time of transition and it can be tough to tell the damaged wood from the healthy wood.  Because of this period of slow decline, we recommend putting off any pruning until you can clearly tell the difference between what is dead and what is alive.

Another reason to avoid haste in getting out the pruning equipment is that you never know when there will be another frost or freeze.  Even dead wood and leaves can be a big help in protecting and sheltering the live wood underneath.  The average date of the last killing frost in lower elevations of Pinal County is March 6.  Remember, it is just an average.  We could possibly still see a killing frost even after that date.  While there is currently a warming trend forecast, I am not ready to say never yet.

I know, those damaged plants look ugly and you may be feeling some pressure to get them cleaned up.  From a horticulture standpoint, there is good reason to delay pruning at least until after the first week of March, and longer if it looks like the weather forecast might still include frost or freezing weather.  When you read this article, check the ten day weather forecast on the Internet and see what it looks like.  If the projected warming trend looks like it is going to hold, schedule your pruning day.  However, weather forecasts can change quickly so be sure to take a look before you start.

Okay, you have decided that the time is right and today is the day to do the pruning.  Here is what you do.  The first step is to get all of your equipment together.  I use a good set of bypass loppers for wood that is larger than a regular wooden pencil.  For smaller stuff, I use a pair of bypass hand shears.  Avoid the anvil types where the lower jaw is flat, not scissor-like.  It tends to crush tender wood that you want to keep.

The next step is to look at the specific plant to be pruned and determine what needs to come off and what needs to stay.  For citrus, you will want to nip back the dead branch tips to a point where all of the dead wood is gone and you only cut only a very little bit of live wood.  I would prune back to a point just above an outside bud.  An outside bud is one that heads in a direction out from the tree, not in towards the center of the tree.  All cuts should be at a 45 degree angle across the twig with the lower point of the cut just above the bud you are going to keep.  Follow the same procedure for bougainvillea and oleanders.

The Queen’s wreath vine is particularly susceptible to freeze damage and most are probably looking pretty bad about now.  The best step is to do the scratch test on major vines down near the ground and see if you can tell dead wood from live wood.  The dead strands are very fragile and will snap off fairly easy.  Live wood will be not be brittle.  Leave those vines in place and retrain them up on your trellis because they will start growing again presently.  Most other vines will be similar.

Finally, lets talk about palm trees.  The palm most susceptible to freeze damage is the queen palm but others can also be injured.  Some make it and some do not.  It all depends upon whether the growing tip of the trunk, the bud area at the top of the tree, has survived.  If it has died, the tree is dead and needs to come out.  If it is still showing some green, I would give it a chance and see if it recovers.  Palms can suffer considerable leaf damage and still be okay.  This is a case where the plant just needs time to recover.

Injured plants need some extra care to help them through the time of their recovery.  Make sure that they are not stressed for water and feed them with nitrogen just before growth resumes.  Since trees are beginning to show signs of budding, now is a good time to get that done.

Frost or freeze damaged plants can be cleaned up at any time but remember that what may seem dead today may actually be simply dormant.

If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande.  The telephone is (520) 836-5221.  The author’s email address is gibsonrd@ag.arizona.edu.

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Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85222
Voice:    (520) 836-5221
Fax:    (520) 836-1750
email:    gibsonrd@ag.arizona.edu