So you’ve decided to garden with native plants. Great! But… which plants, exactly, should you put in your yard? What is native?
The concept of nativeness encompasses two aspects: space, and time. First, where was the plant in question found before humans started moving it to new places? Many resources will answer this question by noting whether a certain plant species was historically found in a particular state. But this is a somewhat arbitrary criteria. Plants don’t know or care about the political constructs we call states. And large states may contain many diverse ecosystems. A species might naturally occur in the forests of northern California, but that doesn’t make it a suitable choice for a yard in the arid southern part of the state.
This is why some resources list native plants by county. But even this doesn’t really have anything to do with the way plants naturally distribute themselves. A plant that has historically lived just over the county line might be a better fit for a site than a plant found in a distant corner of the same county.
For this reason, some native gardeners skip native-by-county and native-by-state lists entirely, and instead look at distance. Any reputable dealer of native plants will be able to tell you where they got the original seed from. (And it should be seed. Reputable dealers do not sell plants taken from the wild; they propagate seeds in their nurseries and sell those plants.) If that naturally-occurring source of seed is within, say, 50 miles of the intended planting site, then the species is native. If the seed is being collected from further away, it is not native, and won’t be considered for that particular garden.
The other aspect of nativeness is time. When we say that a species was found somewhere historically, what do we mean? Kentucky bluegrass, which originally evolved in Europe, could be found across the eastern United States 100 years ago. Does that make it native? What about plants that lived in the northern states prior to the last ice age, got wiped out by the glaciers, and haven’t come back on their own yet? Are they native?
Most people say that if a species was found in a place just before the time that Europeans got there, then it is historically native. But as climate change continues to alter ecosystems, we may want to update our definition of historically native to mean “species that were found in that place when the local climate was similar to what it will be again in the near future”.
Many native gardeners are not purists – that is, they will plant a non-native species in their yards because the species has especially beautiful flowers, or produces delicious fruit, or simply is a personal favorite of the gardener. There is nothing wrong with this. But if we are serious about native gardening, we should at least be aware when a species we are planting is one of these special exceptions. To do so, we first must decide how we are defining what is or is not native in our own yards.