Spring

• There are a number of spring flowering trees and shrubs that will thrive in containers on a rooftop garden. A variety of small magnolias--such as white rose or star, forsythia, lilac, rhododendron and azalea--are great options. When selecting trees or shrubs for a rooftop garden, consider the amount of sunlight that reaches the rooftop. It's possible to erect structures such as lattice roofs that create artificial shade, but again this adds weight that the roof must support.
  
  

Summer

• Hydrangea, gardenia, crape myrtle, dwarf fruit trees and blueberries are easy to grow in containers. Many of these plants require moist soil to thrive. This means you must either have a source of water on the rooftop, or you'll need to carry buckets of water to the plants. Container-grown plants often require water once a day, sometimes more in extreme heat, so factor this in. The fruit trees will drop fruit--so they can create extra work--but if you eat a lot of fruit it's well worth it.
  
  

Fall

• Apple serviceberry, American cranberry bush, black chokecherry, burning bush, doublefile viburnum and sugar maple are ideal for fall, because either their colorful foliage or berries will attract a variety of birds. Larger trees and shrubs will need their roots pruned to prevent them from growing out of the drainage holes and into the roof. It's also a good idea to wrap large pots with some type of insulating material in the fall to help protect the roots in the winter.
  
  

Winter

• Witch hazel, camellia, holly, miniature evergreens and mahonia are ideal choices for the winter garden. Mahonia, camellia and witch hazel flower during the winter months, which adds color to what may otherwise be a dull landscape. Holly, miniature evergreens, mahonia and camellia do not drop their leaves during the winter. Select trees and shrubs that are hardy in at least two U.S. Department of Agricultural hardiness zones colder than the one you're in.