Up On the Roof

Outdoor gardening space is precious. In some areas, it is rare indeed. Apartment and townhouse gardeners use balconies and patios. Roofs offer gardening space as well, but until recent times little emphasis has been placed on roof gardens.

A few urban gardeners used them, but that was about it. In recent years, that changed when local governments began promoting them. The original concept came from Germany about thirty years ago.

These gardens reduce energy consumption, particularly the need for air conditioning. Urban areas are hotter than the surrounding countryside due to the "heat-island effect."

Those living in flood-prone areas might want to plant roof gardens. This can control runoff during heavy rains, and can also filter pollutants from rainwater.

Some governments promote roof gardens through tax credits or cash incentives. They are urging homeowners to install green roofs instead of the usual shingles. Pittsburgh, Toronto, Chicago, Seattle, and Portland, Oregon are all involved in the movement. A roof garden was installed in the Chicago City Hall in 2001.

Roof gardens are required under some building codes. Atlanta, Tokyo, and Chicago mandate that a percentage of all new buildings will have roof gardens.

Anyone considering a roof gardening should keep several things in mind. First, the building must be able to support the garden's weight. For that reason, lightweight pots, paving materials, and soilless mixes are recommended. For decking and paving, use lightweight materials, such as recycled plastic instead of wood. Rubber tiling is perfect for roof gardens. It is lightweight and durable.

Experts suggest that you consult with a structural engineer to learn about the roof's load limit and what the local building codes require.

When designing a roof garden, consider sun and wind exposure. Sun may be so intense that it can actually harm the plants' roots.

Wind is a major consideration for roof gardens and balcony gardens. Some plants are particularly susceptible to wind damage. To learn more about the effect of the wind and what can be done to minimize it, there is no better source than "The Weather-Resilient Garden-A Defensive Approach to Planning and Landscaping" by Charles W.G. Smith, published by Storey. This indispensable guide offers emergency and long-term solutions on how to protect and revive weather-affected gardens, and a complete guide to selecting weather-proof plants. There are chapters on every kind of weather condition that you can imagine-from lightning, fire, and hail to floods, humidity, heat, salt, cold, snow, and ice.

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