Laidback Gardening: Basic tree growth
By Robert Kourik
It’s still not too late to prune many trees.
Fruit trees like apples and pears have not started blooming in most gardens. To prune correctly, we need to know a bit about how a tree grows.
The large fat bud perched on the tip of each shoot is called the “apical bud,” “terminal bud,” or “tip bud.”
It’s very important to know that a tip bud sends a constricting hormonal signal down the shoot to stop all the buds below from becoming either shoots or flower buds. At the same time, the tip bud makes rapid growth skyward. Both effects are very much dependent upon gravity or, at least, the position of the shoot.
Buds that haven’t yet made up their minds as to whether they want to become a shoot (vegetative growth) or a flower bud (fruiting growth) are called “dormant” buds; it doesn’t mean they are deciduous.
An apple or pear “spur” begins as all blossoms do, as a single flowering bud on the fruiting tree that was formerly a dormant bud. Apple and pear trees must take a season to divert all the proper foods and hormones to convert dormant buds into young flower buds on second-year shoots. But the critical difference with spur-type plants is that they continue, on apple and pear trees, to flower and fruit at the same spot on the branch or limb for many years thereafter—as much as twenty years or more.
Get an Angle on Fruiting—Limb Position for Fruit
As a general rule, the tip buds on vertical shoots have the most stifling influence on lower dormant buds and make the most length per season. The tip bud on a lateral at an angle of 45 to 60 degrees has much less impact, and some dormant buds will become either new lateral growth or flower buds and at the same time tip growth will slow. A tip bud on a horizontal lateral causes most of the dormant buds on the horizontal shoot to “wake up” and become new vertical shoots. At the same time, nearly all tip growth stops. Pruning new growth to the ideal zone of position (45 to 60 degrees from horizontal) will promote more laterals without extra pruning and make some flower buds that will become fruiting spurs.
With fruiting and ornamental trees, the foremost guideline is to prune out the three Ds—dead, diseased, and dysfunctional shoots or limbs. So often the gardener is reminded to remove all dead “wood.” The hope with removing dead tissue as soon as it’s spotted is that pests, rots, or diseases won’t progress any further back to kill the entire plant. Next, remove all diseased growth. Nature has equipped most plants with various chemical zones to fight the progression of dying tissue, which compartmentalizes rot and “walls it off” from the inner portion of the tree.
Sometimes two or more shoots, branches, or limbs will cross. If the effect causes a “raw” wound, one of the two should be pruned off with a cut to its base. The rationale is that the raw wound will let insects or pathogens enter the plant.
Another common suggestion is to remove any weak growth. Only practice and trial-anderror will help you distinguish growth that is slender or slight (weak).
Finally, you should remove all true “suckers”— those quick-growing, vertical shoots that arise from the roots.
Now that I have a captive audience (I hope), I’d like to mention summer pruning because it is very helpful in producing more fruitful trees and controlling unwanted growth on ornament trees. While most people prune almost exclusively in the late winter or early spring, I prune mostly in the summer to control growth, promote fruiting, and shape the foliage. (More on this in later columns.)
There’s an awesome way to produce a flower bud or shoot growth. The hormones of a tree move around in a way that allows you to place a shoot or fruit bud exactly where you want one.
There is a hormone that sends a signal from the tip of the branch down to the buds below, telling them not to sprout. By scoring a notch above a dormant bud, the bud does not get this hormonal signal from the apical bud and sprouts into a shoot.
The carbohydrates of a tree must be stored in a bud for it to form a flower. When carbohydrates are generated, they are often sent down the limb into the trunk and roots. Notching below the bud stops the carbohydrates from traveling down and instead stores them in the bud. This causes the dormant bud to form a flower bud.
Notching works best on shoots that are one or two years old and two to four weeks before full bloom. To notch, take a 3/8-inch round rat tail file and use it like you’re playing the violin. Score above or below the bud just deep enough to remove the green tissue under the bark. Be sure to score at least halfway around the shoot. So, one twist of the wrist and you’ve got a new shoot or flower bud. That’s not much effort.
Robert Kourik is the author of: “Lazy-Ass Gardening”, “Understanding Roots”, “The Insectary Calendar”, “Drip Irrigation for Every Landscape and All Climates”. This article is an excerpt from Kourik’s book, Lazy-Ass Gardening.