Wait until spring to prune or replace damaged plants

Advertisement

Except for some very protected areas, there was extensive damage done to some landscape plants by freezing temperatures during the past week. Most of this article will be spent talking about freezing damage and what to do, or not to do, about it.

First of all, I would not do any pruning of any freeze-damaged plants at this time. Don't let anyone talk you into removing plants or pruning them until we get through the winter. We just don't know how much damage has been done for at least a week after freezing temperatures have occurred. And we do not know if we are going to get more.

Check the late night sky. A high likelihood of freezing damage occurs when we have clear skies and low temperatures. If we have cloud cover, temperatures will not get as low as when we have clear skies. If freezing temperatures are accompanied by snowfall or rain that turns to snow, temperatures will be less damaging. Hope for precipitation during freezing temperatures and clear skies.

A light freeze to plants occurs when temperatures dip slightly below freezing for just a short period of time. Edges of leaves are damaged, usually towards the top of the plant. As freezing temperatures continue, the whole leaf succumbs. The second day after a light freeze, leaves that were damaged begin to dry out and scorch around the edges. Damage progresses down the plant as temperatures drop and the length of time below freezing increases.

If temperatures are low for long enough, next the youngest wood begins to freeze and die followed by older wood higher in the plant. As temperatures continue to get lower, or freezing temperatures persist for longer hours, damage continues down the plant towards the soil.

When temperatures drop to lows as they did during this past week, it would be considered a hard freeze. The first sign that a hard freeze occurred to plants with leaves is a limp and water-soaked appearance to the leaves as soon as temperatures rise above freezing. A water-soaked appearance looks like the leaves were just pulled out of boiling water; leaves are limp, dark-colored and lose their shine, no longer having a vibrant color. Freezing ice crystals forming inside the leaves punctured them, releasing their fluids and giving them that flaccid, dull and lifeless appearance.

The last part of the plant to get damage is what we call the crown; that portion of the stem just above the soil. In many shrubs or vines, if the crown is killed, the plant will no longer be salvageable. In some cases, if the crown can be protected, there is a chance the plant can be renewed from the crown. This is why I encourage people to pile mulch or soil around the crowns of their plants just prior to freezing temperatures. Of course this does not work well for trees.

In plants such as bougainvillea, protecting the crown will at least give the plant a chance to regrow from the base if it survives. Plants that regrow from established root systems and a surviving crown will grow extremely rapidly and reestablish themselves quickly.

Now let's talk about plants in containers. Plants in containers may become more threatened during freezing temperatures than those same plants in the ground. Let me explain why. The tenderest part of a plant is its root system. In past eons, there has been no reason why plants had to evolve roots that were tolerant of below freezing temperatures. The ground froze around the roots and insulated them from very cold temperatures.

If you have plants in containers, irrigate them just prior to the freezing temperatures. Water freezing inside the containers around plant roots will help insulate them from very low temperatures. If soils in containers are dry, it's possible the temperature surrounding the roots could drop to the same temperature as the air outside. This would be particularly true if these containers are in windy locations.

Generally speaking, healthy plants are more tolerant to cold weather than unhealthy plants. However, cold sensitive plants fertilized late in the season with a high nitrogen fertilizer are less tolerant to freezing temperatures than those plants left unfertilized.

So what to do now if your landscape has been damaged? Give your landscape one week to see how much damage has occurred. Clean up any obviously dead leaves or trash that has accumulated from the freeze. Don't prune anything. Plant dieback does give some protection to tender plants by providing some flexibility in pruning later in the season.

If you must prune back, don't prune all of the dead or damaged tissue out of the plant. Leave some damage remaining on the plant. Finish your pruning and clean up after danger of freezing has passed. Last year we had freezing temperatures in some parts of the Valley as late as the first week in March. Normally, we would be out of danger by the tail end of February.

Question: I was just told by someone that I needed to give my trees what he called deep root fertilization. He told me that if I didn't do this then all of my trees would become root bound, which would kill the trees. Have you ever heard of this? Am I missing something?

Answer: No, you are not missing anything. You can fertilize a tree or shrub with a shovel or fertilizer stakes. Deep root fertilizing is a method used that is fast and can get into the tree's root zone and beneath the grasses.

If trees are fertilized just by fertilizing the lawn, nitrogen will not get to the tree roots very well. Grasses are great nitrogen strippers. They just strip out the nitrogen from a fertilizer if it is just applied to the surface of the lawn.

You can deep root fertilize a tree growing in a lawn by using a shovel, pushing it into the ground around the tree and distributing fertilizer this way under its canopy. Do this while the ground is wet. While the shovel is pushed into the soil to a depth of about 6 to 8 inches, push on the handle away from you and drop in the hole about quarter cup of fertilizer. If you put the fertilizer too shallow you will burn the grass. Push the soil closed with your foot.

Do this about every three feet or so in concentric circles around the tree. Start the first circle about three or four feet from the tree, the next one about three feet wider than the first. Do these circles all around the tree until you reach the dripline or the end of the branches of the tree. Water the fertilizer into the soil well after you do this.

Remember that this is only for trees or shrubs in a lawn. If they are in a desert landscape with rock mulch, you will put the fertilizer beneath the drip emitters and let the water from the emitters push the fertilizer into the soil to the roots.

A quick and clean way is to use tree fertilizer stakes in place of a bag of fertilizer. The stakes are more expensive but they are easier to use, not as messy and they are slow release. I would do either of these methods any time in mid to late January.

The Master Gardeners of Southern Nevada are offering free gardening classes on Tuesdays and Thursdays beginning Feb. 6 from 7 to 8 p.m. Sessions will be held at the University of Nevada Cooperative Extension Lifelong Learning Center, 8050 S. Maryland Parkway.

All classes are taught by certified Master Gardeners. Community members may get a copy of the class agenda and reserve a space by calling the Master Gardener Home Gardening Help Line at 257-5555. Only preregistered individuals will receive notes from the classes.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension.