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How to Build a Green Roof

Like any gardening project, careful preplanning improves the prospects for success. Professional landscapers lay out a grid, and determine what plants to use in each section, either for aesthetic effect, or as a source of edibles. So your first step is to determine just how much space you want to cover with your initial project. Then carefully lay it out in numbered 2 ft. by 2 ft. squares.

The next step is to determine which plants to use. You’ll need guidance from a local nursery. Your best bet is to go with plants that thrive in your area. They should have shallow roots and be able to withstand mild drought conditions. And, of course, they should be perennials.

Rather than try to grow the plants on the roof, lay out 2’x2’ plastic trays, with sides that are less than 4 inches high, on the ground. Prepare them with a growth medium of compost and gardening soil and set your plants. Water lightly and wait a few days until the plants are well established.

If you have the space, you can position the trays on the ground to obtain the look you want from your roof garden. Then number the trays corresponding to their location on the grid.

The trays will weigh about 50-60 pounds, so you’ll need some help getting them up to the roof. Maintenance requires occasional watering and perhaps some weeding and insect control.

Jack Star is a former bureau chief covering many of McGraw-Hill's trade and technical publications. He now writes extensively on gardening and using the earth’s resources wisely.