We recently learned that Tigard, OR, a town of about 48,000 people that is part of the Portland metro area, has implemented an impressive soil volume minimum for trees planted in streets and parking lots: up to 1,000 cubic feet of soil per tree.

Here is how the City of Tigard summarizes this change on their website:

The new regulations include minimum soil volume requirements for parking lot trees and street trees. The soil volume standards for street trees are outlined in Section 12 of the Urban Forestry Manual and are based on the width of the non-street portion of the right of way. The soil volume standard for parking lots trees is 1000 cubic feet of soil volume per tree. Appendices 11 through 15 of the Urban Forestry Manual include example soil volume plans specifications and calculations. 

In addition, parking lots are required to be designed to achieve 30% tree canopy cover at tree maturity. Section 13 of the Urban Forestry Manual includes the Parking Lot Tree Canopy design requirements. Appendices 16 through 18 include example parking lot tree canopy plans, specifications and calculations. 

Tigard’s soil volume requirements for street trees varies by width of right-of-way. Image: City of Tigard Urban Forestry Manual.

You can read the complete list of standards and regulations in Tigard’s Urban Forestry Manual. Meantime, we will be updating our ongoing list of all municipalities with soil volume minimums to include Tigard.

Thanks to Nick Kuhn, Community Forestry Coordinator with the Missouri Department of Conservation, for letting us know about this! If you know of a city or town with a soil volume minimum that we’re missing, please email us at [email protected] so that we can keep the information there up to date.

Flickr credit: Andy Nystrom