The city trims trees in the right-of-way and boulevard areas for safety and tree health reasons. Typically, trees are trimmed or pruned when they obstruct vision at traffic control sign or intersection, or branches extend over the street past curb line. Tree trimming improves tree health; removing damaged limbs encourages wound closure. Trimming may also correct a defective form to reduce branch failure during windstorms.
Pruning is best done in the winter because the trees are mostly inactive or dormant, and pruning at this time maximizes wound closure in the growing season and reduces the chance of transmitting disease. If you wish to do your own tree trimming, we recommend this shrub and tree trimming guide from the University of Minnesota.