Thank you for the great question. 

A New York City tree needs to be able to withstand the general street pollution and winter salting of the roads as well as adapting well to container life.  Ilex opaca (American holly) is a great tree for the city: tolerant of salt and generally pest free. It grows very slowly but does eventually reach up to 30 feet tall which may be overwhelming for even large containers.  It needs some protection from winter wind and harsh afternoon sun.  Ilex x attenuata 'Fosteri' is another good holly for a container.  It grows slowly but will reach 30 feet like the American holly.  One of its great appeals is that it bears berries without the presence of paired male and female plants.

There are quite a number of smaller conifers that make excellent container plants and would give you the all-year greenery that you are looking for. Our guide Conifers as Container Plants has a great list of plants to consider, most of which will stay significantly smaller than the American holly and grow slowly.  It also will give you information on the soil and cultivation considerations of conifers in containers.  The Chamaecyparis obtusa (Hinoki cypress) and Thuja cultivars listed are particularly well-adapted to a well lit city location.  I suggest that you also look at our Urban Gardening guide for information on care of city dwelling plants.

Please let us know if we can be of further help.

Courtesy of NYBG Plant Information