To some naturalists, “native” is neither relative nor debatable

Done right, native plant gardening supports wildlife and delights the eye. Here a gray hairstreak butterfly samples some butterfly-weed. — Photo by Matt Pelikan

April is the month when Island gardeners start to hit their stride, and over the next month or two, an astronomical number of plants will be seeded or transplanted into Vineyard gardens. In keeping with the emerging desire for eco-friendly solutions, more of the gardeners I know are factoring the environment into their gardening and landscaping plans — reducing fertilizer use to protect our groundwater, selecting plant species that can fend for themselves without the need for pesticides, and growing species that offer resources for wildlife.

But available information on how to accomplish these goals is often quite general, rather than Vineyard-specific, and in catalogs and other marketing materials, hype occasionally outweighs substance. Here is a quick look at one of the key concepts of eco-friendly gardening: native origin. Native plants are widely assumed to be “better” than non-native ones, the theory being that a native plant species is already part of the local ecosystem, and therefore growing it represents an addition of useful wildlife. Native species are also widely assumed to be well adapted to local conditions, and hence easy to grow without fertilizer, pesticides, or supplemental water.

This is all true — to a degree. But if ever there were a word that depends on context for its meaning, this is it. In the broadest context, “native” may simply mean a plant that occurs naturally somewhere in North America (in contrast to our many food and ornamental plants that originate on other continents). In seed catalogs that have national distribution, or plants produced by large growers, I’d assume that this very broad definition applies unless the product description adds further details. For regional suppliers, “native” may mean “native to New England.” But even this narrower definition has remarkably little practical value.

Our growing soils and climate are a far cry from those found in subtropical Florida or the rainy Pacific Northwest, and plants originating in those regions are as foreign to the Vineyard as many species from Eurasia. This is not to say that such plants shouldn’t be grown here. But learn to look beyond the “native” tag to consider the cultural conditions the plant needs. If such species provide ecological advantages or are easy to grow here, it’s because they’re chosen for compatibility, not because they are “native.”

At the other extreme, conservationists and hard-core native plant enthusiasts often use this slippery word to mean “a species that occurs naturally on the Vineyard,” or, in an even more specific sense, to denote plant material (individual plants, not a species as a whole) that originates on Martha’s Vineyard. The thinking here is that, because the Island is an island, our wildlife populations are separated from mainland populations, subject to unique conditions and pressures, and hence have evolved distinctive traits that make them especially well adapted to living here. By growing plants that are “native” in this restrictive sense, the thinking goes, you’re helping preserve the unusual wild heritage of the Vineyard, and you’re avoiding the introduction of off-Island genes that might weaken our local populations.

Again, there is truth here, but also complexity. For one thing, the hypothesis of distinct Vineyard genotypes has never really been tested by research. It’s a plausible hypothesis, and if there are unique Vineyard genotypes, they’re surely important to preserve. My guess is that some of our local populations are indeed distinctive and, in some cases, may harbor genes that have been lost (or never appeared) in mainland populations. This is an important, if untested, possibility, and it is appropriate to be cautious about protecting such unique traits.

But for the many plants that have some way of sending their genes over long distances, there may be more contact between Island and mainland populations than one might expect. Windborne seeds or pollen grains can easily cross a few miles of water, and for many plants, seeds can be transported for miles in the guts of birds that have eaten them. For these plants, there may be little difference between Island and regional mainland populations.

Moreover, even very local origin is no guarantee of suitability if a plant is set in conditions that don’t suit it. Even if you’re lucky enough to find Vineyard-origin plant stock (at plant sales at Polly Hill Arboretum, for instance), or if you grow your own from seeds you’ve collected, you still need to keep in mind the ecological requirements of the plants. Properly sited, they’ll furnish a splash of carefree Vineyard authenticity in your garden; improperly sited, they’ll die as quickly as any other plant that’s in the wrong soil type or doesn’t get the right amount of sun. And for some of our local wildflowers, the range of what’s suitable can be quite narrow indeed.

I’d encourage all Island gardeners to experiment with “native” plants, by any definition; in particular, local-origin specimens truly can provide a gorgeous, trouble-free show while contributing to the local ecology. But don’t assume that the “native” tag, by itself, guarantees ecological benefits or makes good gardening practices unnecessary.