Sunday, December 20, 2009

Woodman, Spare That Tree!

Pruning season is upon us....

"Put down the chain saw, sir, and step away from the tree!" It's pruning season again. A time when we rejuvenate our fruit trees and roses, make our shade trees safer and stronger, and increase next season's bounty of flowers and fruit. But it's also the time of year when the combination of y-chromosomes and 2-cycle engines can cause irreparable damage in the landscape.

Rule #1: a chain saw is not a pruning tool. It could be in the hands of a skilled professional. But for the most part, chain saws are excellent for cutting firewood, cutting up wood which has already been removed from the tree, and sculpting logs into garden art. For that matter, machetes, axes, and hatchets are not pruning tools, either. They are brush-removal tools.

Rule #2: shade trees should be pruned by qualified professionals, or after you have been properly trained. A certified arborist can assess your trees for you. Most shade trees which have been trained properly when young need very little pruning when mature. It's mostly a matter of removing crossing branches, branches which are too closely spaced (<12" apart on the trunk) or are at weak angles (30 or 45 degrees). Branches should be removed in stages and cut to leave a collar.

Good pruning tools make the job easier and more effective. My primary pruning tools consist of a folding saw, a pair of hand-held bypass pruners, and a lopper. A pole saw is useful for pruning fruit trees and light thinning of shade trees. I have found pole loppers cumbersome and dangerous, though they are handy for topping tall hedges and for summer pruning of fruit trees. Sharpen the cutting blades of pruners frequently with a flat file, and keep them oiled.

What do we prune now? Roses, deciduous fruit trees, deciduous vines, and shade trees. Hardy evergreens can be pruned anytime fall through spring; avoid pruning them during very hot weather. Our general goals are to open up the structure of the plant, control the size if necessary, make them safer (better branch structure), increase the flowers, and reduce diseases. See our separate articles on rose and fruit tree pruning. Today we're going to focus on other flowering woody plants.

What are the plants we don't prune right now? Subtropicals are best pruned during warm weather. That includes evergreen fruit trees such as citrus and avocadoes. They are somewhat tender, and open pruning wounds are vulnerable to frost damage. The only reason to prune Citrus trees is for size control or aesthetics. Unlike other fruit trees, we don't need to reduce the amount of fruiting wood. Prune anytime between March and October.

Subtropical plants which have been damaged by freezing weather should be left alone until spring. The cold snap on December 18 and 19 did a lot of top damage to plants such as Angel's trumpet, bananas, Bougainvillea, and Lantana. The freeze wasn't cold or sustained enough to have killed them, but they look pretty bad. You can gently tug off the blackened leaves and stems if you like, although they actually do provide some measure of continued frost protection simply by 'cloaking' the remaining parts of the plant. Wait until new growth begins in the spring, then cut back to that. As with citrus, pruning may make the plant vulnerable to further damage. The plant will tell you when and where to prune.

Hardy deciduous shrubs, trees, and vines which flower in the spring could be pruned now. It wouldn't hurt them. But since we mainly grow them to enjoy the flowers, why not wait until after the bloom? This includes shrubs such as Chaenomeles (Flowering quince), Deutzia, Forsythia, Lilac, Spiraea (Bridal wreath), and Wisteria. Trees grown primarily for their flowers include crabapples, flowering and red-leaf plums, flowering cherries, and saucer and star magnolias.

Garden books will tell you that these plants bloom on "old wood." If you look closely, you can see the fat flower buds, which formed last summer, all ready to open. In fact, you can cut branches of these and bring them into the house to get an early blossom indoors‹especially plums and quince. The main purpose of pruning these shrubs and trees is to control the size or enhance the form. Head them or thin them just after the bloom. Wisteria is primarily pruned to control the rampant growth. You can cut off vigorous shoots anytime, including summer. The flower buds are very obvious now, so if you want to prune just work around them. But if you need to cut Wisteria back severely (it can get a little out of hand), just enjoy the blooms first.

If it is a deciduous shrub or tree which blooms in the summer, chances are it flowers on "new wood" and can be pruned now. The best example that is common locally is crapemyrtle (Lagerstroemia). It blooms at the end of new growth, so no matter how hard you prune it back it will still flower. As such, it's an ideal plant for people who like to prune! As long as you leave it alone once the season's growth has begun, you will get flowers. I have a crapemyrtle seedling which sprouted in a perennial border, where I don't want anything bigger than 3 ­ 4'. So I just cut it to the ground each winter, and it blooms as a nice low shrub each summer.

If your crapemyrtle's size is not a problem, just trim off the seed heads now (or do nothing at all). If you want to keep it a particular size, just cut out an amount equal to last year's growth. Most varieties grow 2 ­ 4' a year, so that's how much you'll need to remove to maintain a particular height. Although you can head the growth if you must, it will look better if you can cut to a point where an existing branch already is growing.

Hydrangeas seem to perplex folks, especially the large "mophead" hydrangeas (H. macrophylla). These are the types that come in pink or blue, with flower heads 6" or more across. Pruning in the winter, or too late in the summer, reduces flowering considerably. They mostly bloom on "old wood" which forms in mid to late summer. So if the gardener in your household prunes your old-fashioned hydrangeas when he prunes the roses, you aren't going to get flowers. There are some new types such as 'Endless Summer' which rebloom on "new wood."

The fact is that hydrangeas don't need to be pruned at all. But if the shrub has grown too big, cut it back after the spring bloom, but before August. Older shrubs can be thinned by about 1/3 to rejuvenate them, sparking new shoots from the base. These guidelines also work for Oak-leaf hydrangeas (H. quercifolia), which are also easier and generally better-looking shrubs in the Davis area because they're not fussy about our soil and water conditions. PeeGee Hydrangeas (H. paniculata) conveniently bloom on new wood, so you can whack them to the ground in the winter if you like. If you want way more information than you ever though possible about hydrangeas, check out

Prune in winter: roses, summer-flowering trees, hardy fruit trees, shade trees.

Prune after they bloom: spring-blooming shrubs, trees, and vines.

Prune spring through fall: subtropicals.

Prune fall through spring: hardy evergreens.

Prune with a chain saw? Nothing, ever!

"Woodman, spare that tree! Touch not a single bough! In youth it sheltered me, And I'll protect it now."
-- George P. Morris (1802 - 1864)

From the Davis Enterprise Dec, 26th 2006

1 comment:

  1. Prune after bloom, I like that a lot. A very simple guideline to follow, and correct at that!

    -Samudaworth Tree Service
    Tree Removal Brooklyn