Canopy Pruning Time is Around the Corner
Here’s why pruning a sapling and mature tree matters to your property and the trees’ health.
Benefits of Pruning (direct and indirect benefits)
Pruning should be a regular and planned component of tree care in the urban setting. Though trees in the forest don’t need pruning this is because they live in entirely different macro- and microclimate and niche conditions. Meaning, they have a diversity of microbes in their soils to help them fight disease and increase cell repair when disease or pests do feed on the plants. The trees standing together and with understory and thus are not exposed to the same wind strength. Forests create microclimates at soil to canopy level that are at least in part, responsible for the far longer life span of a forest tree (about two to three times longer than that of a lucky, healthy, urban tree).
Sapling and mature tree pruning provide a variety of benefits to you the property owner and the tree. This list includes direct and indirect benefits such as:
Tree defense system is enhanced by
1. removing stems that tax the plant but don’t return a lot of photosynthates,
2. decreasing disease and pest pressure by increase air and light flow through the canopy,
3. favoring healthy leaf growth and increased photosynthesis which is the way a tree makes the food needed to fuel cell/tissue/organ repair and growth,
4. reducing wounding damage from crossing branches,
5. reducing wound expansion through poor cutting procedures.
Property safety and values are enhanced by:
1. reducing probability of limb break or tree fall onto a target (e.g. house or car),
2. improving aesthetic with direct increase in property values and perception of property (how much of market valuation is perception based after all😊),
3. increasing canopy greening and thereby reducing AC costs (depending on what the canopy is shading).
Pruning Deciduous Trees
There are three main aspects to a mature trees canopy, the trunk, scaffold branches, and laterals. The leader is the extension of the main trunk and in most urban trees one leader is selected early on in sapling development and maintained. This ensures both strong branching connections and the aesthetic of a full rounded or pyramidal canopy.
The leader of a deciduous tree should have branches angling at greater than a 30-degree angle from the main trunk, alternating down the leader-to-trunk in a spiral pattern. These are the scaffolds. BTW, the optimal branch angle is between 45 and 60 degrees, but many trees have a natural architecture or have grown without training, requiring a bit of leeway.
Know what form your tree naturally takes – is it pyramidal (magnolias and many pear species) or can it support a wide bulbous canopy (e.g. maples and oaks)? This will help you to visualize how to prune the sapling and young tree and let you know what to expect from the pruning cuts of your Certified Arborist.
Pruning can be 1) canopy thinning, 2) canopy lift, or 3) canopy shaping. Canopy thinning increases the flow of light energy and air through the canopy thereby reducing pathogen infection rates and maximize photosynthesis. Canopy lift accomplishes two major tasks. First, it raises the canopy to avoid contact with people, cars, buildings. Second, it increases photosynthetic efficiencies by shifting leaf resources to the canopy parts that “see” the sun. Canopy shaping can both maintain or develop the desire aesthetic as well as remove limbs (scaffolds or laterals) that are damaged or crossing.
All deciduous trees are best pruned when dormant. Due to increased disease pressure from the climate crisis these trees MUST be pruned when dormant: oaks; maples, dogwoods, elms, tulips, sassafras, and prunus species (apples, plums, pears, etc.). This is NOT an exhaustive list. Sometimes you’ll need to prune species that lose a limb due to unexpected breakage this is when sterile technique is critical. Ask your arborist what their sterile pruning protocols are (see below); if they don’t have any, they should no longer be your arborist.
Saplings and young trees are best pruned every 3 to 7 years based on the growth rate of the tree. Older trees should be pruned ever 7 – 12 years, again based on the growth rate of the tree. Trees growing to close to a property can be treated with growth hormones to slow the trees girth and height growth for 5 to 7 years. Research is showing growth hormones on trees have a tremendous number of beneficial side-effects.
If you are growing trees for fruit production, then scaffolding branches are best pruned after flowing or fruiting. This depends on fruit production the previous year and goals for the present and following years. It’s a whole topic in and of itself and too length to include here.
Pruning Evergreen Trees
The same rules for deciduous apply to evergreen trees except timing. Also, lateral pruning is or can be quite different in evergreen trees. Evergreen magnolias are pruned like deciduous trees (scaffolding and lateral branches). Evergreen hollies are pruned for a dominant lateral though they are quite tolerant of multiple “headers” and very tight branching angles. They simply have a different vascular architecture than other “leaf” trees and as such can fuse limbs and resist breaking in ways completely unique to them (another tree that can be treated more like a shrub, similar to the holly, due to its unique vascular system anatomy is the crape myrtle). Evergreen producing needles are a whole new category in terms of pruning.
Spruces, firs, Douglas-firs can be pruned anytime because they have buds that will sprout if the lateral branch tip (bud tip) is pruned (removed). If you want to increase the bushiness or fill in a ‘bald’ area of the canopy, then this tip pruning will help do just that. You can prune in the spring or winter. The best growth response will happen when pruning is done in the winter and will reduce probability of infection.
Pines (most pines – there are cultivar variations) rarely need pruning unless you are maintaining size and shape. If so, it would be best to get some books specializing on pine tree pruning and then reach out to specialist organization to get the best practices for (candle-thinning) your particular cultivar. This is a wonderful and I think meditative and creative activity, and it requires thought and a willingness to learn from error if you’re inexperienced but passionate about learning.
Yews, junipers, hemlocks, and the many many species called Arborvitae have different pruning parameters. Yews can be pruned anytime of year. Due to the prevalence of diseases hitting junipers, hemlocks and various Arborvitae species hard I recommend pruning them in the dead of winter when temperatures have slowed their growth the most. Sterile pruning is critical. Like shrubs – these trees can have the tips of lateral branches cut without creating dead stem/stubs. Please, please don’t make little boxes or balls out of these plants unless this is the only form that fits your very formal or whimsical garden. Allowing your trees to grow in a natural or organic form will increase the health of the tree, its canopy, and increase the plant’s longevity. Sever sheering causes a loss of stored resources and slows the growth of the roots and the leaves/needles. It also causes the tree to shift resources from repair and recovery to cell growth. Remember, there are limited resources for everything from people in economies to trees harvesting light and soil micro- and macronutrients. If resources are preferentially going into growth, then repair is often limited.
Critical Components of Proper Pruning Technique
Quality of tools
Tools need to be sharpened regularly as well as cleaned using Lysol or a Lysol-like product that kills germs including viruses. A file from any hardware store can sharpen your loppers, pruning shears, hedge shears. I like middle priced tools and keep them sharpened. If you must twist or can’t cut the stem with one try, then it’s too large for the tool you are using, or the tool is too dull. STOP! Pruning cuts need to be quick and clean. For this reason, anvil shears are the worst – please do not use them. They pinch the tissues rather than cleanly cutting them.
Hand saws are a different story and a quality handsaw if you do a lot of pruning, is worth the high price. Silky produces on one of the best hand saws (pole saws also). They are not alone but this will get you started on the path to finding a handsaw that will last quite sometime and produce a clean cut the tree can more readily heal. As for chainsaws, there are only two worth having in my opinion (if gas) and that’s Husqvarna and Stihl. The quality of the chain is key here. A blunt or weak chain won’t last long and will cause damage when cutting. The new battery-operated small models are excellent for being lightweight for those of us heading up the canopy with ropes. Skil has a great little battery-operated chain saw with excellent teeth on it.
Additional general rules of pruning include:
1. remove anything dead or dying,
2. remove downward- growing branches,
3. remove crossing branches (not necessarily both but select one to retain),
4. remove scaffolding branches with diameter equal to or larger than trunk.
Start pruning from the top of the plant (unless raising the canopy) and remove the largest stems first. You’ll want to walk around the tree several times and imagine how different limb removal will air the canopy and/or balance it. The largest limbs/stems are removed first because the goal is to reduce the number of cuts. The fewer the better – for you and tree. Never remove more than 30% of the canopy and if the tree is sick then consider removing only the dead and dying branching possibly leaving some of them to remove the following pruning season. Since many disease branch cuts go back to healthy tissue, even through you’re cleaning the canopy of dead tissues the tree is still being exposed to pathogens and stressed. So, better to break up the canopy “repair” by letting it happen over two to three years.
Below are some sketches of how to prune branches to base of a scaffolding stem or the trunk. There is a specialized kind of tissue growing around the base of the branch. I think of it as a curtain that’s been drawn back and if I cut those curtains they can’t close over the window (or wound). This is NOT at all what is happening anatomically, but it works for learning what to look for and why it matters. You’ll see wrinkled bark tissues and you want to cut just above that but not too much. If you cut too far above, you’ll have a stub and the curtains can’t close over that stub either. The stub (staub) created can also lead to the plant continuing to ‘feed’ it which makes it exceptionally attractive to bugs and infection.
DO NOT dress the wounds by painting or anything else. That old tale has been repeatedly demonstrated to cause additional damage to the tree by trapping moisture at the newly cut site and limiting wound closure.
Figure 1. from Texas A&M, see citations below.
NEVER let anyone climb a living tree with spikes. If they can’t get at the tree with a boom, then they can climb it using ropes. That’s how I climb it and believe me, if this 50-year-old woman can get up into that canopy with a rope – anyone else can. The spikes do a lot of damage (wounds hard to heal) and introduce disease because often, someone willing to climb a tree with spike doesn’t know enough to clean the spikes between trees. Nothing makes me madder-than-a-hatter to see spike holes in a living tree or to see a tree topped. Being a certified arborist doesn’t guarantee high quality or ethical behavior, but it is a good sign for it. Becoming a certified arborist with the ISA requires taking a test (about an hour long) and paying about $400. That’s enough of a barrier for most hackers. Having both ISA and TCIA “certification” means the person/company has opened themselves up to testing and inspection.
Trees are a living, aerobic organism with a massive amount of benefits that are not often known because really, to know them you’d have to take a plant ecology class (or similar), or be a master gardener, or a plant hobbyist. My hobby is not ship building nor ice climbing. I can’t tell you a thing about sailing or the various subtleties of ice or ice climbing gear nor can I write code (well some statistical code) or paint. No one should expect you to know how to properly prune trees. I would like you to know that trees provide cleaner air, more oxygen, can clean water and soils, can increase property values from 10 to 20% (based on size, type, and health of tree), reduce asthma rates, increase outdoor activities, enhance psychological responses, and store carbon. Trees are things of beauty, and without them we would cease to exist. Much of our rain is produced by the amazon, all our oxygen comes from plants, not to mention food and all that wood in housing and furniture. So, I hope you’ll save your trees and optimize the benefits they give you (and us) by investing in their care, health, and longevity.
1. Virginia Cooperative Extension, Virginia State University
2. Tennessee Cooperative Extension, University of Tennessee
3. UMN Extension, University of Minnesota Extension
4. Aggie Horticulture, Texas A&M University
5. Plant Anatomy, James D. Mauseth (a bible for plant anatomy and physiology)
6. Esaus Plant Anatomy, Rey F. Evert