So if nature has to serve urbanism, how can it serve it well? How do we do it right?
Street trees offer shade, shelter and structure to walkers and bikers. Street trees in front of stores and home increase the valuation of goods in stores and the resale value of homes. Trees in windows decrease convalescent time in hospitals and sick time in workplaces workplaces. A full grown tree on the sunward side of a house saves money in cooling bills in the summer. A full grown tree on the windward side of a house saves money on heating in the winter. They also filter out particulate pollutants form the air and reduce the intensity of stormwater flows to streams through adhesion to their leaf surfaces.
Street tree’s roots both anchor the tree and enable it to breathe, pulling water from the ground to keep its leaves intact. If not water can get into the ground, under a new parking lot, for example, then a tree’s roots have no reason to grow there. If there is no air in that ground, then the tree’s roots have a hard time pulling water from the ground in the same way you have a hard time sucking water out of a closed straw. Compacted or clay soils are often devoid of air spaces, causing tree roots to skate along the ground in a search for air. Finally, roots anchor it to the ground. Approximately as much wood is below ground as above ground, but the shape of the root mass is a web if tendrils hugging the surface of the ground. Trees need air to get water form the soil, and that happens within a foot of the ground.
Between the leaves and the roots is the bark. The wood of a tree is strictly for water transport up from the roots to the leaves. The cells of the wood are dead. The living cells that transport the nutrients back and forth between the roots and the leaves daily and seasonally are on the inside of the bark. The life of the tree is within a millimeter to an inch of the surface of the bark. Trees are that fragile.
The most common way for street trees to die in the first year is underwatering. The second most common is misplanting.
The roots need that aerated soil to grow and supply the leaves, so dig a wide hole, with at least 2:1 (width:height) sides. The base of the tree should be at or slightly above the surrounding ground. A conical hole will not do, because the tree could fall into the hole and below the ground surface. Also, a having a pool in the void under a tree could lead to mold issues on the roots. So make a hand packed (not going to collapse) floor in the middle of your wide planting hole as wide as the pot the tree came in. Measure from the ground surface to that flat base. As long as that hole is between 0-2 inches shallower than the dirt in your pot, you are good.
Note, the dirt may fall out of the pot if the roots are not well established or even bound in the pot. Make the hole shallower by adding soil back into the hole.
After the first year of good planting and watering, make sure the bark is intact, and don’t let any tree grates kill off the tree in the meantime. You then will have to deal with the sidewalks, curbs and streets. That’s a bunch of structure that needed to be in place along with the well dug hole. More on that later…