Hawthorne Street, one of my blogging neighbors in Prospect Lefferts Gardens, the northeast reaches of greater Flatbush, posted some tips about how to watch over new street trees planted this Spring:

If you have a recently planted street tree in front of your house or building, maintenance is a key factor in ensuring that it continues to be healthy. The first year after planting is a critical time. Now that the danger of frost is dissipating, young trees need a lot of water. Watering should be done slowly, allowing the moisture to permeate the soil deeply. This allows the tree to develop a deep root system rather than depending on shallow roots.
– Caring for new street trees

They have additional info, and links to other online resources, so check ’em out!