What Trees Do Well on an Urban Roof Deck?

Small Trees

• A roof deck typically has a weight limit, unless it's been specially designed for a garden with heavy trees and shrubs. Sticking with small trees can eliminate the need for thicker substrate layers on the roof and stay within weight limits. A large number of landscape, ornamentals and fruit-bearing trees have dwarf varieties that only grow to a given size and still provide beauty, and even partial shade, if planted in groups or placed near sitting areas. With proper care and watering, these trees can do just as well on a roof as they do on the ground. The Improved Meyer (Citrus x meyeri) lemon tree, for example, is disease free and does well in outdoor containers year-round in zones 8 and 9. It provides fragrant blossoms and sweet lemons -- and only grows to about 6 feet tall when grown on a dwarf stock.

Container Trees

• Container trees tend to be much smaller than their in-ground counterparts. They also eliminate the need for a soil layer on a roof deck. The ability to tailor growing media to the particular needs of a given tree makes them more likely to survive. They can also be moved quickly to an area protected from wind, frost or heat, if necessary, depending on the type of tree and weather. Trees that need partial shade may do especially well if surrounding structures cast shadows part of the day. Japanese maple (Acer palmatum), for instance, works well as a container plant for roof decks in zones 6 through 8, as it grows only between 6 and 10 feet tall and provides attractive foliage in cooler months.

Resistant Trees

• Rooftop conditions may not always be ideal for trees. In urban areas, the heat-island effect typically causes slightly higher temperatures than the city's rural and suburban areas, according to the Environmental Protection Agency. Smaller trees relatively resistant to your climate's hotter temperatures can fare well, especially if you choose a variety native or adapted to your climate. Wind-resistant trees also fare better than those needing substantial wind protection. For a drought-tolerant tree, Flowering Crabapple (Malus hybrids) works well, and it is cold hardy down to zone 3, but can withstand heat up to about zone 8, so it can tolerate some heat. It provides colorful blossoms, foliage and fruit at various times throughout the season.

Trees with a Specific Purpose

• Consider what you're looking for in a tree for your urban roof deck. You may want a larger tree that provides shade and be willing to make structural changes to do so -- or you may want a container tree or two with ornamental blossoms or seasonal foliage color. Very fragrant trees work well if you plan on using the deck as a place of relaxation, recreation or for dining. Leonard Messel (Magnolia x loebneri), for example, is a medium-size tree offering ornamental blossoms and a strong fragrance, which works well for a relaxing garden or to provide shade for a reading or eating area. It is hardy from zones 5 to 8.