PRUNING: Is it time to thin my trees and cut off the lower limbs? My answers to these common questions might surprise you. There seems to be an abundance of curious tree-pruning advice still around. Let’s try to straighten it out.
Pruning too much is the most common mistake. Few trees need major pruning every year. Other than some fruit trees, few trees need annual thinning and, unless lower limbs are a physical problem, they should be left on the tree.
TIMING: Landscape trees can be pruned any time of the year, but the best time is from fall to late winter. Fruit trees should be pruned from midwinter up until bud break. Certain fruit trees like peach trees, should only be pruned just before bed break because pruning induces bud break and flowering. Early flowers and late freezes spell no fruit.
AMOUNT OF PRUNING: Pruning trees is part science and part art. Don’t try to change the character and overall, long-term shape of a tree, and don’t remove lower limbs to raise the canopy. Low growing limbs exist for a reason. It’s very unnatural to strip tree trunks bare. If you think that looks good, think again. Remove dead, diseased, broken, or damaged limbs and the weakest of crossing limbs. Remove limbs that grow toward the center of the tree and limbs that are dangerous or physically interfere with buildings or activities. Thinning to eliminate a certain percentage of the foliage is usually a mistake. Heavy thinning of a tree’s canopy throws the plant out of balance, inviting wind and ice storm damage. The resulting stress attracts diseases and insect pests. Gutting (heavy interior pruning) is never appropriate.
PRUNING CUTS: Pruning cuts should be made with sharp tools. Hand tools such as bow saws, Japanese pruning saws, loppers, and pole pruners are good for small limbs. Chain saws can be used for larger limbs, but only with great care and a thorough understanding of the equipment.
Flush cuts should never be made. Cuts leaving a 1/16” stub are also bad. Pruning cuts should be made at the point where the branch meets the trunk, just outside the branch collar. The branch collar stub will be as small as 1/8-1/4” on small limbs but can be several inches to as much as a foot or more wide on large limbs. It will also be wider at the bottom of the limb than at the top. Cuts made at the right place leave a round wound. Improper flush cuts leave oval cuts and cause cavities to form in the trunk long term.
It’s scientific fact that cutting into or removing the branch collar causes problems. Flush cuts encourage decay. They also destroy the natural protective zone between the trunk and the branch and can cause several serious tree problems including discolored wood, decayed wood, wet wood, resin pockets, cracks, sun injury, cankers, and slowed growth of new wood. Proper cuts are round, smaller, and heal much faster. Peach, plum, apricot, and other fruit trees are particularly sensitive to flush cuts. Many fruit tree insects and disease problems are related to improper pruning cuts. Long branch stubs can also detrimental sometimes and should be avoided, however, it is always better to err on the side of stubs too long than too short.
WOUND DRESSINGS: Research by Alex Shigo, Carl Whitcomb, and the U.S. Forest Service has shown that pruning paint and wound dressings have no benefit and can be harmful by slowing the healing process. Healthy tissue needed for callus formation can be damaged or killed by pruning paint or dressings. Trees have defense cells, much like white blood cells in mammals. These lignin cells are produced on the backside of a wound to naturally prevent diseases from entering fresh cuts. Just as a cut finger heals faster when exposed to the air, so does a tree wound.
CAVITIES: Cavities are often caused by flush cuts. Cavities in trees are voidswhere fungi have rotted healthy material. They are usually the result of physical injury. Removing only the decayed material is the remedy. Fillers such as concrete and foam are only cosmetic and not recommended. When removing decayed matter from cavities, be careful not to cut or punch into the living tissue. Injuries to healthy tissue can introduce further decay into the healthy wood. When cavities hold water, drain tubes are sometimes inserted to release water. Bad idea. Drain tubes puncture the protective barriers between the rotted and healthy wood and allow decay to expand. I don’t recommend any of the trunk injector systems for fertilizer and insect control because of their puncture wounds, plus they miss the main problems in the soil and root system.
CABLING: Weak crotches between limbs can sometimes be stopped from splitting by installing cables horizontal to the ground so the natural movement of the tree is not completely stopped. Cabling used to hold up low growing limbs is poor tree care and a waste of money. Cabling can be very dangerous and should only be done by professional arborists. In most cases, I do not recommend it.
As a final note, the tree trimmings and sawdust resulting from pruning should not be hauled away. The large pieces should be used for firewood and the limbs and foliage should be shredded and used as mulch under trees or mixed into a compost pile.
FERTILIZING: Since all plants require food, trees should not be overlooked when a landscape is fertilized. The easiest way to fertilize trees is in conjunction with the general fertilization of the grass and planting beds beneath the trees. The feeder roots are near the surface, and the tree will utilize whatever nutrients are there. Remember that over 80% of a tree’s root system is in the top 12-18” of soil.
Putting fertilizer in holes drilled throughout the root zone is not a good idea for general fertilization, but is effective for a specific deficiency such as chlorosis. The roots will take the pure material (sulfur, iron, or magnesium, (for example) away from the cores as needed. What’s better is to feed the entire root zone with compost and quality organic fertilizers.
A good balanced, organic fertilizer is perfect for establishing a healthy condition for trees. Fertilizer should be applied two or three times a year, as with other plantings. Placing a layer of compost over the entire root zone of the tree (and beyond) will help greatly to feed the soil and thus the tree. Healthy plants will repel insects and diseases, reducing or eliminating the need for pest control products. Periodic applications of foliar food are also beneficial. The best foliar feeding products are aerated compost tea and Garrett Juice. See Appendix for the formula.
AERATION: Mechanical hole punching of the soil is recommended for tree care, especially in clay or other heavy soils. Oxygen is one of the most important elements in healthy soil. Air penetration helps greatly to stimulate microbial activity and root growth. Physical aeration help is only needed in the first year of any organic program. Healthy soil will have natural aeration.
PEST CONTROL: Occasionally trees need to be sprayed to control certain pests, or to give them a little extra nutrient punch. In an organic program, this can be accomplished in one step, reducing the cost once again. Garrett Juice and aerated compost tea are again the best tools. Foliar feeding will indirectly help control most harmful insects without killing the beneficial ones. At the same time, the sprays provide nutrients for the tree. Foliar feeding helps with pest control by improving the immune system of the plants and by feeding and stimulating beneficial microorganisms. When orange oil or d-limonene is added at 2 ounces per gallon of spray, the spray actually kills pests. It will also kill beneficials so use sparingly.
One of the most persistent pests is the aphid, which is the most prevalent in the spring when trees start their active growth cycle. Aphids damage plants by sucking the juices from tender, new growth. There is a very easy way to control aphids – spray with garlic/pepper tea, or molasses and orange oil, each at 2 oz. per gallon of water. A water blast followed by the release of ladybugs is my favorite aphid control because it doesn’t hurt the beneficials.
Protecting and adding to the beneficial insect population will give effective control of aphids and other harmful insects. Good insects include ground beetles, spiders, ladybugs, green lacewings, praying mantids, wasps, mud daubers, but there are many more.
Taking care of trees using common-sense techniques and safe products is easy and cost effective. The results are better than using toxic chemical treatments, which will destroy many beneficial insects while only reducing a percentage of the target pest insects. Imagine being able to spray trees without worrying about wind drift, lawsuits, over-application of material, and the real possibility that the environment is being harmed each time a pesticide is applied. That’s the beauty of tree care using the natural approach – it is safer and it works better—in every way!