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.