Tree and plant varieties serve a very important purpose in ornamental horticulture. In unnatural urban areas, where the environment can be unforgiving, plants are not always given the opportunity to evolve. In
U.S. cities like Philadelphia,
Washington, D.C., and the average life of a street
tree is an average of 7 years. In
harsher environments, like New York City
with its lake effect winters, the average life span can be even less. Chicago
In Ecological restoration seed provenance is a key principle. If you were installing a rain garden in essence you would be mimicking a flood plain. Imagine a flood plain near a river. The river and the flood plain have been there for thousands of years. Throughout fluvial changes, human impact, diseases, pests, and weather fluctuation the flood plain has existed and evolved as a plant community. Some plants have died, but many have thrived because of there genetic diversity. Now recreate that in your yard…tomorrow.
I may have heard and collective audible gasp. Relax. This is possible. It can be done by planting plants grown for locally collected seed. Provenance is the origin and location of the collected seed. The seed contains the DNA of the plants in that region so they should react in the same way to similar conditions; say within a 200 mile radius of where the seed was collected. If you were to plant a variety, a clone propagated from either tissue culture, budding or grafting, it may not have the same chance to evolve. Clones are selected mainly for specific characteristics. These characteristics could be drought tolerance, heat tolerance, or a specific flower color. A plant may have been cloned in a region or country where a local plant disease does not exist. When planted in mass in your rain garden it now does not have the tools to evolve, adapt, or over come this disease. Another example of this could be extreme weather conditions in a certain region.
How so you know which plants to use? This is easy. While planning your project visit a natural area that is similar in your local area. When purchasing you plants ask you local garden center or nursery what the provenance is for the plants you are purchasing. Most nurseries keep records of their seed collection sources. Make sure you are buying straight species rather than varieties. For example, Acer rubrum (Red Maple) is straight species but Acer rubrum ‘Red Sunset’ (Red Sunset Red Maple) is a variety that is commonly cloned by tissue culture for its brilliant red fall display. These things will help your ecological solution be successful.