Tree Pruning

Poor tree architecture (structure) tops the of list of causes for tree failure. Often failed trees must be removed at high financial and aesthetic costs to landscapes.  Pruning is far less expensive than tree removal and, when properly executed, will extend a tree’s life span and save landscaping expense.  Tree owners are cautioned that incorrect pruning can do the opposite, causing structural and health problems that lead to tree failure.  (see Improper Pruning Techniques below).

In forested environments, competition from other trees is useful, causing trees to develop strong structure (a single leader and smaller lateral branches). Also, forested trees support each other by sharing the work of breaking winds.  In “built” environments with unlimited sunlight, trees often need assistance to develop strong structure.

Basics of Structural Pruning

1. Develop and maintain a central leader. 
2. Identify the lowest branch in what will become the permanent crown. 
3. Prevent branches below the permanent crown from growing larger than half the trunk diameter. 
4. Space main branches along the central leader. 
5. Reduce vigorous upright stems back to lateral branches.
6. Suppress branches with weak branch attachments.

Improper Pruning Techniques

1. Topping [pdf] a tree.
2. Lion's tailing a tree (removing branches from the interior of the canopy, leaving foliage just at the ends).
3. Leaving branch stubs.
4. Cutting off the branch collar (making a flush cut).
5. Removing more than 25 percent of the foliage in a single year.
6. Using wound paint (unless pruning an oak during oak wilt season).
7. Climbing the tree with climbing spikes.

Pruning Timing

Pruning in late winter, just before spring growth starts, is ideal.  Fresh pruning wounds are exposed for only a short period of time to winter temperatures, reducing the chance of winter injury. This all aids in reducing the chances of infection and decay.  Pruning in the dormant season also allows branch structure to be easily seen, which makes pruning decisions more clear. Although dormant season pruning is ideal, pruning throughout the year for most species is acceptable.

Species Specific Pruning Restrictions

1. Oaks should be pruned November 1st-March 31st. Due to oak wilt concerns.
2. Ash should be pruned October 1st-April 30th. To reduce spread of emerald ash borer.
3. Apple, hawthorn, mountain ash should be pruned February 1st-April 15th. 
4. Species affected by black knot and cankers should not be pruned during warm, wet periods of the year (i.e. spring).
5. There may be a slight variation of these dates based on weather conditions.  

Contact us for a consultation regarding your pruning project.

We plant trees with the hope and expectation that it will grow long into the future, becoming a healthy, mature tree.  However, most trees obtained from traditional nursery stock (in containers or balled and burlapped) come with defects which are rarely corrected prior to planting.  Often these trees are planted too deep or have encircling roots which eventually “girdle” the tree and lead to negative outcomes. 

To establish a long-lasting tree, it is essential that excess nursery soil be removed from the top of the root system, exposing the root flare and removing any encircling roots. When planting the tree, you must make sure the root flare is left exposed and above the final soil grade. Think of trees in the forest where each flares out at the bottom.  A tree that looks like a telephone pole sticking in the ground was likely planted too deeply and potentially has stem girdling roots.  (See more information in Planting Resources below)

Basics of Species Selection

1. Fit the tree to your site. Account for tree growth when selecting the location or tree species.
2. Assess the soils and sunlight, choose a species which will do well in existing conditions, rather than trying to change them.
3. Diversify your yard. If you only have one or two species one insect or disease could come along and kill half or all of your trees (like emerald ash borer). Insects and diseases typically attack all the species (silver maple, sugar maple, etc.) within a genus (maple, oak, pine, etc.). So focus more in genus diversity rather than species.
4. Find out what hardiness zone you're in. The greater Duluth area is anywhere from 4b to 3b. Look at the interactive USDA map to find out what you are: USDA Plant Hardiness Zone Map [website]

Contact us for assistance with species selection or your tree planting needs.

If you are not sure who's property a tree is on, there are some online resources which may help. Check the St. Louis County Land Explorer [website] and zoom to your property. The property lines are reasonably accurate. If the tree looks close to the line you can contact your city or county engineering department who may be able to help.

Trees provide a long list of benefits, but certain defects can turn a tree into a liability. We can provide you a comprehensive Tree Risk Assessment, taking into account the likelihood of tree failure and targets at risk of being damaged by falling debris. In some situations the likelihood of failure can be reduced by pruning and tree support systems (cabling and bracing).