1. What Defines a Native Plant?
I love using native plants in landscape design, but what exactly is a native plant? From my point of view, there are several layers to the definition of a native plant, and it is important to understand the differences.
1. Native to California
In my experience, when most people in the landscape industry use the term California Native Plant, they are referring to a plant that is native to any location within the California Floristic Province. This more or less falls within the State boundaries, encompassing a wide variety of environments, each with a variety of plant communities. This definition seems a bit too broad to me to achieve the full benefits that a native plant should provide. For example the California Fan Palm (Washingtonia filifera) is native to certain deserts in southern California, a radically different habitat from that of the moist foggy valleys of the northern coast that are home to the Coast Redwood (Sequoia sempervirens). For a map of the California Floristic Province see http://en.wikipedia.org/wiki/California_Floristic_Province
2. Native to a particular region
More important in my mind is to use plants native to the particular region you are designing for. To me this is the more accurate definition of a native plant: a plant that would have grown naturally in a specific region, for example using the Coast Live Oak (Quercus agrifolia) for a garden along the eastern edge of the San Francisco Bay. When talking about why to choose a native plant over a non-native, the list of reasons usually involves fitting into the local environment and benefiting native insects, birds and other animals. So planting a Shaw Agave (Agave shawii) that is native to the southwestern edge of California in a Marin County back yard is not really living up to the full intent of this idea.
3. Native to a specific place
If we are trying to use plants that fit into the local region, how do we draw the lines between those regions? The San Francisco Bay area is most certainly considered a distinct region, but the climate, soils, and animal life vary greatly between San Rafael and San Jose or San Francisco and Walnut Creek, especially when you are looking at the area before European settlement. How specific do we need to be to get the maximum benefits of using native plants? I have often been asked “exactly what would have grown on this piece of land before it was developed?” This is about as specific as you can get and is a sort of ecological restoration approach to native plants, but in my mind is a bit too literal. The best way to approach this, in my opinion, is to look at the Native Plant Communities that would have existed in the general area of a garden prior to development. For example, the eastern edge of the San Francisco Bay was mostly Oak Woodland and Grassland; along with the Coast Live Oak (Quercus agrifolia) there were woody shrubs like Coffeeberry (Frangula californica), grasses such as Purple Needle Grass (Nassella lepida), and flowering perennials like the California Poppy (Eschscholzia californica) among many others. From these Plant Communities you have a pretty good selection of plants to choose from.
Of course most garden sites are not pristine natural environments, quite the opposite in fact, most have been extremely altered by many years of development. Especially when looking at a small yard in a highly urbanized area, the climate, drainage, soil structure, soil chemistry and even subsurface water flow may have been altered. So it may be difficult for plants from the area’s native plant Communities to thrive as they once did. This takes us into a topic that will have to be covered separately – Why use native plants?
References:
Designing California Native Gardens – the Plant Community Approach to Artful, Ecological Gardens, by Glen Keator and Alrie Middlebrook
California Native Plants for the Garden by Bornstein, Fross and O’Brien