Keeping Trees in Good Health

Like the houses they protect and adorn, trees need regular care, sometimes by professionals. You can perform the routine chores of low-level pruning, fertilizing, and pest control, but tasks such as bracing limbs with guy wires, or climbing to a high perch to cut them off, should be left to a specialist.


Judicious pruning can improve a tree’s health. But because each cut wounds the tree, you can also do harm if you prune carelessly.

A tree walls off a wounded area with cells and chemical barriers that keep disease-causing organisms from invading healthy tissue. These guardians develop at the base of each branch in a swollen area called the branch collar.

Part of the collar is destroyed by pruning a branch flush to the trunk, a method favored in the past; the wound closes slowly, if at all. Cutting too far from the trunk is also a poor practice, since the stub is too far from the source of protective cells. To close properly, cuts must be made at a precise angle, just outside the collar (page 99). Leave the wound untreated, or apply a thin coat of asphalt-based tree paint. Other paints retard closure.

Do your pruning in late winter or early spring, before the buds open. Prune flowering trees just after the blooms fade, and remove any broken or diseased branches from all trees immediately.


To maintain normal growth, trees need a variety of nutrients, often provided in the form of fertilizer. Among the most effective fertilizers are organic materials such as cottonseed meal, bone meal, or blood meal.

Fertilizer works best when it is spread on the ground or injected as a liquid (pages 102-103). You can also spray liquid fertilizer onto a tree’s leaves (page 104), or hammer fertilizer spikes around the drip line (page 102). However, if the drip line is 30 inches or less from the trunk, do not use spikes.

The best time to apply fertilizer is in late autumn, when all the leaves have fallen and trees begin storing nutrients for the winter. You can also fertilize in early spring; for flowering trees, wait until they begin to bloom.

Whatever season you choose, avoid overuse of fertilizer. One or two applications a year is enough for young trees, and once every 3 to 5 years for mature ones.


If a tree looks sickly or harbors bugs you do not recognize, call your local extension service for a diagnosis. The prescription is likely to be a spray-on chemical, which must be handled with care. You can safely spray a tree up to 25 feet tall with the equipment shown on page 104. Hire a professional to treat larger trees.

Before you start, check local laws governing chemical spraying and study the instructions on the package label. Some pesticides must be mixed with water; dilute them exactly as directed. Wear protective clothing and keep children and pets out of the area.

TOOLS Pruning shears Lopping shears Pole shears Pruning saw Broadcast or trough spreader Root-zone injector Spray canister Garden-hose sprayer MATERIALS Dry fertilizer Tree spikes Fertilizer cartridges Liquid fertilizer Pesticide

If you prefer a nontoxic treatment, try dormant oil, a commercial mixture of mineral oil and water. Sprayed on a tree in early spring before leaves emerge, it coats and smothers aphids, scales, and mites, even before they hatch from eggs. Read the directions on the label carefully. Although harmless to humans, the oil can damage evergreens and certain species of beech, birch, and maple.

Another nontoxic approach is biological control, using a pest’s natural enemies. A single ladybug, for example, can eat four dozen aphids a day, while a bacterium called Bt attacks gypsy-moth and other caterpillars but is harmless to other organisms. Ask your nursery operator or extension agent about pest fighters indigenous to your area.


Wear gloves when handling fertilizers. Add goggles when cutting tree branches. Follow manufacturer’s instructions precisely when spraying pesticides. Depending on toxicity, you may need to don not only gloves and goggles but boots, long sleeves, and a dust mask or cartridge respirator, as well.



The basic guidelines

Well-formed young trees have a straight central branch, or leader, extending from the top; the main limbs have U-shaped crotches evenly distributed around the trunk at least a foot apart vertically. To maintain this strong, balanced framework, prune away any undesirable features: Remove branches having a tight, V-shaped crotch, which makes a weak joint. Cut off suckers or water sprouts—which can grow anywhere on a tree and have no lateral branches—as well as any buds from which new suckers and water sprouts might grow. Dispose of branch stubs, dead or broken limbs, and small branches that grow toward the trunk or across larger limbs; crossover growth can damage the trunk and other branches by rubbing against them. Periodically thin inner branches of mature trees to admit light. On deciduous trees, remove low limbs that keep you from walking under the tree. Leave the lower limbs on evergreens in place.

Proper pruning cuts

Two features of a branch govern the position and angle of a pruning cut—the thick collar at the base of the branch and the dark ridge in the bark of the parent branch or trunk. On mature deciduous trees, trim branches off square near the collar (solid line, above left). Do not cut into the collar or the ridge, and do not leave a stub (dotted lines). A branch on a very young deciduous tree or an evergreen may have a large collar and a bark ridge that encircles the base (above, center). Prune just outside the collar and parallel to the bark ridge (solid line), neither leaving a stub nor cutting into the ridge or the collar (dotted lines). In a year or so, a hard callus should form at the edge of the wound (above, right), later closing over the cut.




Shearing small sprouts

Use pruning shears to sever buds and small branches that are up to ¼ inch thick. Cut as close to the trunk as you can without damaging the bark.

Cutting off small branches

To remove a branch up to 1 inch thick, set the cutting blade of a pair of lopping shears on top of the limb, with the side of the blade against the trunk or supporting branch. Angle the lower blade away from the bark ridge and the collar, and bring the handles of the shears together in a single smooth motion. Do not twist the shears or use them to tear the branch from the tree. If the shears do not make a clean cut on the first attempt, sharpen them or switch to a saw.


Extendable shears

Pole shears can cut branches as big as 1 inch in diameter and reach branches up to 15 feet overhead. The pole consists of a telescoping plastic or wooden shaft. A cutting blade under a stationary hook is operated by a cord that runs through a pulley to increase leverage (photograph). Place the hook over the base of the branch in the position shown here. Wrap the cord once around the pole to keep the shaft from bowing, and pull the cord sharply. Cut close enough to the branch collar so no stub remains. If the severed branch hangs in the tree, pull it down with the head of the shears, taking care not to break other branches.




Removing the branch

When cutting a branch that is up to 3 inches thick, first trim off any secondary limbs. This will serve to lighten the branch and keep it from catching in the tree as it falls. Use a pruning saw to cut halfway through the bottom of the branch, about a foot from the trunk; this cut will stop bark from tearing loose when the branch falls. About an inch outside the first cut, saw through the branch from the top. When this second cut is halfway through the branch, the limb will snap off, leaving a stub.

Trimming the stub

For the third cut, saw 1 inch into the underside of the stub, just outside the branch collar and at a right angle to the stub. Make the fourth cut at the crotch of the stub, just outside the bark ridge at the base of the stub (right). Support the stub with one hand and saw downward to meet the third cut.




Mapping for surface fertilizer

Lay a string or garden hose around the tree at the drip line, which is directly below the tree’s outermost leaves. Mark a second circle about two-thirds of the way in from the drip line to the center, but not less than 5 feet from the trunk. Mark a third circle about twice the drip-line distance from the trunk (inset). Using a broadcast or trough spreader, spread tree fertilizer over the area between the inner- and outermost circles.

Placing tree spikes

Mark the drip line of your tree as for surface fertilizer, above. For each inch of trunk diameter, drive a spike into the ground along the drip line. Space the spikes evenly, and while hammering, shield the tops with the protective plastic cap provided.




Preparing a root-zone injector

Along the tree’s drip line (opposite), mark spots for an injection every 2 to 3 feet. For a tree having a trunk more than 4 inches in diameter and widespread branches, mark a second circle halfway to the trunk and plot injector locations along it (inset). Consult the fertilizer box for the number of fertilizer cartridges needed for each inch of tree trunk diameter. Divide the total by the number of injection points to get the number of cartridges per injection. Load the root-zone injector for one injection by unscrewing the reservoir cap and dropping in water-soluble fertilizer cartridges. If the reservoir is too small for all of them at one time, replenish the supply as the fertilizer dissolves.

Using the injector

Close the water-flow control valve and connect a garden hose to the injector. Turn the water on to a medium flow, and open the control valve on the injector just enough to permit water to trickle out of the tube. Slowly push the tube into the soil, twisting it back and forth until it reaches a depth of 6 to 8 inches. In hard ground, allow the water to soften the dirt and ease the way. For trees with shallow roots, set the control valve halfway between off and half on; for more deeply rooted trees, set it to half on; for very large, well-established trees, start at half on, then turn the valve to on after the first minute. Leave the injector in place until the fertilizer has dissolved, then turn the water off, pull out the tube, and move to the next injection spot.




A pressurized canister

To fill the canister, remove the pump assembly. Pour liquid fertilizer or pesticide into a small amount of water in the canister, then add the rest of the water needed to dilute the chemical. Mix powdered chemicals thoroughly with the full measure of water in a bucket before pouring it into the canister. Screw in the pump, and vigorously raise and lower the handle several times to pressurize the tank. Aim the nozzle upward and squeeze the pistol grip to saturate the undersides of leaves. Adjust the fineness of the spray, if necessary, by turning the nozzle tip, and repressurize the tank whenever the spray weakens.



Filling the sprayer

Pour concentrated liquid fertilizer or pesticide into the reservoir, using the ounces scale on its side to measure the desired amount. Add water slowly while watching the gallons scale, stopping when the mixture reaches the level that matches the amount of spray solution you need. Screw on the spray mechanism, close the water valve, and gently shake the sprayer.

Using the sprayer

Connect the sprayer to a garden hose and open the spigot. With the sprayer pointed at the tree, open the water valve; when spraying dormant oil, saturate both the trunk and the limbs. To control the force of the spray, turn the garden-hose spigot. Direct the spray upward with the nozzle deflector. Doing so allows you to keep the sprayer level enough for the suction tube to siphon chemicals into the spray.