Unlike most major cities, in Denver, property owners are responsible for the care and maintenance including pruning of their street trees even though the trees are located within the public right-of-way. This requirement is established by the Revised Denver Municipal Code (Chapter 57).
As the street trees in Stapleton mature, trimming is beginning to become an issue as branches and foliage start to interfere with safety and ease of pedestrian sidewalk passage. Furthermore, passengers trying to get in and out of cars parked on the street may encounter interference from tree branches.
Exceptions are allowed for young trees which would be irreparably damaged by premature pruning. Trees require little if any pruning during the first five years after planting and that pruning should be limited to the removal of dead and broken branches. If pruning is done too soon or too severely, it slows root growth and encourages shoot growth which adds significant stress to the tree and makes it more vulnerable to insects, diseases, and stress from drought. After five years, if a tree is healthy, it should have a strong, established root system and should be pruned every three years, tapering down to less frequent pruning as the tree becomes more than ten years old. The amount of live branches that should be removed varies based on the age of the tree and the growth rate of the species.
Once your street trees are established enough to be pruned, consider hiring a licensed arborist with certification from the International Society of Arboriculture to trim your trees so that it is done correctly and does not cause damage to the tree, a valuable asset for your home. If you do undertake trimming yourself, please refer to the Existing Forestry Rules & Regulations governing Trees & Tree Care listed in the resource section below to ensure that proper techniques are followed for the health and wellbeing of your tree. Do not indiscriminately remove branches as this can add stress to the tree. Pruning should be based on pruning objectives (why to prune) and pruning methods (how to prune) which determine the type of pruning cuts to be made. Objectives include reducing the risk of breakage from wind and snow, improving the structure, maintaining health, improving aesthetics, providing clearance, improving view, reducing shade, and increasing flowering and fruiting.
Light pruning to remove a few small branches can be done at any time of year. More extensive pruning should be done in late winter to early spring. This is advantageous because wounds close more rapidly if done just prior to when new shoots emerge, there are few active insects and disease spores to infest pruning cuts, and deciduous trees have dropped their leaves so it is easier to see what you are pruning. Lastly, many tree companies offer discounts for winter pruning.
For more information:
Revised Denver Municipal Code (Chapter 57) – The City Foresters Ordinance http://www.denvergov.org/Portals/626/documents/Trees/City%20forester’s%20ordinance.pdf
Existing Forestry Rules & Regulations governing Trees & Tree Care – http://www.denvergov.org/Portals/626/documents/Trees/Trees%20and%20tree%20care%20regs.pdf
CSU Extension, Colorado Master Gardener Program, CMG Garden Notes: http://www.cmg.colostate.edu/gardennotes.shtml#pruning
#614 – Structural Training of Young Shade Trees
#616 – Pruning Maturing Shade Trees
#617 – Structural Pruning of Maturing Shade Trees