Heavens above - rooftop gardening

Sunset, Spring, 1997 by Steven R. Lorton, Rosalva Welsch

Exposed to full sun and drying winds, pots quickly lose moisture. Keep potted plants well watered - never let them dry out.

Consider the weight. If you are planning to use a lot of pots, or several big ones, weight might be a consideration. If you're in doubt about the strength of a roof or deck, consult a structural engineer.

Check out the rules. If you live in an apartment or condominium, consult with the manager or condominium association. Rules vary: some buildings have no restrictions; others do not allow overhanging plants or water features; a few do not allow gardening at all.

Choose the right plants. Many perennials do well in pots and will take the extremes of high-rise living. Choose plants for their sturdy, handsome foliage, and consider the bloom a bonus.

Vines do well in big pots. Climbing a wall or trellis or running along a rail, they can add color, provide shade, and create a privacy screen. Akebia (A. quinata), clematis, climbing roses, grapes, and wisteria can all be grown successfully in generous containers.

Care for container plants. Repot perennials every couple of years. Refresh soil in annual pots yearly. If the soil has not compacted, you can reuse it; just add organic matter and mix in some granular plant food, well-rotted manure, or controlled-release fertilizer.

The trick to keeping a small tree happy in a container is root pruning. Every three years, pull trees out of their pots between late November and early March. Pull the big roots away from the rootball and cut them back. Then replant the tree, adding new soil. Scatter some controlled-release fertilizer on top of the soil and water well. In the spring, new feeder roots will shoot out to support the tree.