What's Coming Up 181: Special focus on frost damaged trees

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Many landscapes are built around a Japanese maple, so when they're damaged, even non-gardeners take note. If a tree that's important to you lost some or all of its leaves to frost this spring, read on. Then you can help the tree recover and also know what to say to protect it from the saws and axes of impatient, uninformed others. 

What's Coming Up Issue 181:

a special one-subject issue, with this summary:
Continue to wait
on these trees that are replacing all their frost damaged foliage. DON'T PRUNE YET. Their push of growth is not done. What seems dead may only be slow, and is salvageable. Give them another week.


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Special must-do this week

Frosted tree tapped its reserves, now needs our help

My Japanese maple took such a hit from the frost last month. It dropped pretty much all of its leaves. I figured I'd wait and see if it grew back. Would fertilizer help? Someone said to give it lots of water. I sure hope it's not dead. - M.P. -


Overall plan:

For Japanese maples and other trees hit hard three weeks ago, patience was all that they needed from us. During the first weeks after that kind of leaf loss, the ball is entirely in the plant's court. Later -- NOW! -- as new leaves and shoots appear, we can help by watering, being vigilant and (maybe) fertilizing. Down the road as the replacement growth matures, we can prune out dead and weak wood.

Understanding why:

After a sudden leaf loss, cells in branches capable of making new shoots switch quickly into a high gear. They will push out new growth from where leaves were lost and even from under the bark. This growth is built entirely from starches stored over the previous few years in those twigs and branches. We can't inject anything into the wood, and we can't add anything via the soil because nothing is coming to that wood from the roots (See Portrait of a virtue). No worries, however. A tree always stores extra starch. It has reserves even after a major loss. The tree that's been healthy in the past, has the best future.


After three to four weeks, we see new growth. As those new shoots reach the light, photosynthesis resumes. That restarts the "draw" on the water conducting system, so roots begin to absorb water and nutrients, and start growing again. Right now it's critical that we keep the soil moist.

Also, fertilizer may help. Best for this use:  Something water soluble in several weak applications. Look for fish-, seaweed-,  or acid-loving plant products.


Why this tree or branch, but not all?

Frost damage is complex to the point of mystery.

Some trees were hit hard by the spring frost. Many Japanese maples lost all their leaves.

(Not only maples were involved: Other trees and shrubs were zapped and are now starting over. This issue's information applies to azalea, cherry, ginkgo, mulberry, yellowwood, etc.)


Right: This is Nature at her most mischievous. She coaxed this red leaf upright Japanese maple -- and many other trees -- into early leaf with a precocious spring, then killed off all their foliage in a frost. However, the tree's far from  dead. (You might want to take steps to keep it from being killed!) Having defoliated so early in the year, it may even recoup all losses by the end of the growing season.



Right: Other trees took partial hits, keeping foliage on inner and lower limbs or on parts of their canopy shielded by overhanging trees. The sides of this tree may have escaped the frost because they extend over loose, open soil that was "breathing out" warm air during the night. The damage occurred on limbs overhanging the junipers, where the ground's warmth may have been trapped beneath the evergreen boughs.




Below: This tree was spared by its genes, proximity to bigger tree,s and the warmth trapped within the open porch. Damage occurred mostly to limbs hanging over the paved walkway.



Is it dead? Sure looks dead.


Deciduous trees survive complete defoliation every fall, so don't declare such a tree dead just because it has lost leaves. Instead, check a branch for flexibility and scratch an expendable twig to look for moist green tissue in the cambium -- the bud-producing layer below the bark.


Below: Scratch a twig with your fingernail, or...


...snip off a section looking for moist green just under the bark.


Signs of life

Watch for new growth, remembering that it may be obscured by dangling dead foliage.



Right: This bud formed where a twig meets a larger limb. It formed on the branch collar in advance of any new buds on the twig itself because starch content is still high here in the collar. Starch within the twig is depleted because it was tapped to fuel spring leaf-out.

Buds may yet erupt on the twig, once remaining starch in the twig is shifted and concentrated where it can support that growth.


Hard-hit trees make the prettiest comeback because complete defoliation promotes a stronger growth response.

If you have a half-hurt tree water and watch it, too. Its net loss is or will be equal to the defoliated tree

We know quite a bit about maples' use of starch because it is not only a plant fuel but a food crop -- dissolved into the sap, it becomes the sugar in maple syrup.

Just as other trees' sap can be made into sugar, what we know of maple starch accumulation, use and movement can be applied to other woody plants.

Now you know what to expect

...we bet if you look now at a tree 3-4 weeks out of frost damage, you will be delighted about finding lots of spots and fresh shoots like these on your tree:


Portrait of a virtue: Why we wait to help these trees

At the time a tree's leaves are suddenly killed,

there's nothing we can do to help. Some things we might do, can hurt. At this time, patience truly is a virtue. We wait.


Roots cease to absorb water and nutrients within hours of sudden defoliation;

some even die back. So the tree has no immediate need for water or fertilizer.


A leafless tree is not drawing moisture from the soil,

so repeated watering may make the soil soggy. More roots will die if the soil becomes waterlogged. Feel the soil first, and water only if the soil is dry at finger depth.


Fertilizer does not stimulate growth.

After a plant itself "decides" to push new growth based on light, temperature and availability of starch stored in its wood, fertilizer might then support that growth.


A tree may use its old leaves for their starch.

Some of the starch to produce new shoots and leaves will be withdrawn from dead leaves' stem bases. So don't pull off dead leaves. Let the tree reabsorb what it can. The leaves will fall when they dry.


Don't remove branch tips,

because the dormant buds at the tips of branches are a tree's most effective directors of new growth. Although some of the tree's branches may die as a result of the defoliation, you can't predict which ones. So hold off pruning until the tree's new growth shows you what's too weak to re-leaf.


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