Plant trees in an appropriate manner to the street or highway landscape:

• When planting trees along parkways and curvilinear suburban roads, near interchanges and overpasses or in similar situations that would typically have the potential to be park-like or natural in appearance, plant a diversity of species in informal patterns to mimic nature.
• When planting trees in such urban settings as grid streets with planting strips or downtown, formal planting approaches (for example, trees planted in a row with similar spacing) are appropriate. In sidewalk situations like those downtown, plant trees in elongated planting wells, as opposed to small round wells with grates, so that roots have adequate space for trees to live longer.

Space street trees in such a manner that the crowns of large deciduous trees typically grow to touch or nearly touch each other.

• This principal should be used whether planting street trees “on center” or in creating informal or more natural landscapes. Street trees that will grow to a large size should be spaced about 50 feet apart. Trees in more natural settings, like parkways, interchange areas or where roads run parallel to parks, can be spaced even wider.
• Smaller or under-story trees can be planted in between or among large trees, depending on the situation.
• In urban settings, tree spacing may vary and be less than the recommended 50 foot separation, depending upon:
  • Available space along sidewalks, given underground utilities and vaults, fire hydrants, curb cuts and similar factors
  • The width of the street and the species that is chosen in that context (for instance, some of the medium-sized species are good choices along narrow downtown streets where they can grow to maturity and provide canopy over streets and sidewalks)

In choosing a mix of trees along grid streets with sidewalks, choose species that will have similar proportions when they grow to maturity.