Just four of the 1,457 trees to be planted are evergreens. Evergreens don’t do well in urban settings. The tiny pores lining their needles get clogged with salt and pollutants. Their cone shape also makes them less appealing to designers because they take up precious real estate. And they don’t offer shade.

Designers had initially planned Norway maples for one area. Earlier this year, a state task force listed it as a potentially invasive species—it grows so enthusiastically it chokes out other plant life. State officials have proposed banning the maples and 139 other species from being imported. Elm trees, however, will be welcomed back. These new varieties, headed for the financial district, are disease-resistant, Under the greenway’s design plan, there will also be pear trees, Bloodgood, London plane trees and honey locust trees. The new trees will be placed in specially manufactured soil that will allow air and water to easily reach their roots. That should help them survive in soil that in spots is just 26 inches deep. And, at least initially, rain won’t be enough to quench the trees’ thirst. Pipes along the surface of the soil will water the trees and aerate the ground; another pipe lower in the ground will provide drainage. If everything goes as planned, they should grow at least a couple feet a year.