Many Of Our Urban Trees are planted in small holes surrounded by overly compacted soil. Their roots are never given a chance to escape these holes and the trees are forced to live out the remainder of their short lives, essentially, confined to pots.
Planting with the Pogo Park Team in Richmond!  To mitigate the compacted clayey conditions (limited oxygen availablity), we dug the whole parkway strip down to 3 feet and amended the soil with compost.  As compost breaks down, it leaves open pockets of air within the soil.  Remember, nothing gets into a root without being bonded with an oxygen molecule.  Roots require oxygen to function!
When preparing a site for planting, creating the necessary cubic footage of rootable soil for healthy root growth is the extremely important.  Rootable soil is a soil medium that is compacted less than 80% ASTM, has oxygen levels between 6-16% and has sufficient available moisture and nutrients with no toxic substances. Small trees require 600 cubic feet of good quality, non-compacted rootable soil to reach a mature size and live a full life.  Medium trees require 1200 cubic feet and large trees require over 2000 cubic feet of rootable soil.  These numbers are somewhat flexible depending upon factors such as soil texture, level of soil compaction, moisture availability, and the specific plant materials used. 
In limited urban spaces, there are a number of treatments that can increase available soil and encourage deeper root development, thereby avoiding root related hardscape displacement.  Structural Soil is one such method.  Please click on the navigation bar to learn more about Structural Soil and how to Make Your Own.

Planting Site Preparation

Choosing Quality Nursery Stock is important. The Urban Tree Foundation has produced excellent Specification Guidelines for Container-grown Trees for California.

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  Rootball Preparation