No matter whether the City plants a tree, or you do it on your own at your own expense, the adjacent property owner is responsible for watering through the 2-5 year establishment period. After that, you will only need to water during times of drought. You will need to keep the tree planting area weed-free for the life of the tree.
You are also responsible for annual mulching. This will help to control weed growth, and will keep moisture in the root zone. Additionally, when you mulch the root zone instead of installing turf, there is no need to mow grass in an area where there is a risk of damaging the delicate trunk bark of a young tree.