My last post discussed why it’s important to include native plants in our gardens. But how many native plants does it take to make a significant difference? Do we actually have to uproot and abandon cherished exotics to have a garden that gives back?
How Many Plants Need to be Native?
A multi-year study released in 2018 found that the tipping point is reached at a ratio of 70% native biomass to 30% exotic. In a breeding territory containing 70% native and above, chickadees (the sample bird studied) were able to successfully rear enough young to sustain their populations. Below that, they weren’t.
A good place to start is by surveying what’s already on your property. What is a native, contributing member to the larger ecosystem and what is merely pretty? Of the merely pretty, what do you really love? Lastly (but importantly), what, if anything, is invasive?
In my hedgerow, for example, there are seven trees and twenty-four shrubs. (Bear with me through some numbers here, okay? I know numbers can be boring, but it gets better.)
Of those seven trees, six are native and the seventh is a Washington Hawthorn (Crataegus phaenopyrum). The hawthorn, while native to the U.S., isn’t quite native to my ecoregion, its range stopping short just south of the Northeastern Coastal Zone, where I garden.
Moving to the shrubs now, twenty of the twenty-four are native. The non-natives are various cultivars of common lilac (Syringa vulgaris).
All told, this works out to a ratio of about 84% native to 16% non-native biomass. The ratio will be made even more favorable next year, when I plan to add various native grasses and herbaceous perennials to soften the edge between hedgerow and lawn.
Neither the hawthorn nor the lilacs are invasive. And I love the beautiful, fragrant lilac blossoms and bright red hawthorn berries.
So I enjoy both guilt-free. And the “bird hedge” is, indeed, alive with birds in all seasons.
For an easy way to begin familiarizing yourself with plants native to your zip code (if you’re in the U.S.), be sure to check out the Native Plant Finder. As a bonus, the tool organizes plants not just by native range, but by the number of caterpillars hosted. Bird lovers rejoice!
What the Native Plant Finder doesn’t do (at least not yet) is tell you what type of site these native plants are adapted to, such as full sun, gravelly soil, dry shade, etc.
To help you match native plants with your site-specific growing conditions, here are some of my favorite references. (What I really enjoy is that the authors are not just highly-knowledgeable experts, they speak of the plants as though they’re speaking of good friends. It makes them fun to read!)
- Native Plants for New England Gardens by Mark Richardson and Dan Jaffe (Covering 100 species, this is a great primer for anyone gardening in New England.)
- For an encyclopedic reference library covering all of North America, I recommend the following books by William Cullina. They’re out of print now, but keep your eyes open at used book stores or check your local library. These three have been on my bookshelf for years and I continue to refer to them as needed:
- Prairie Moon Nursery has a wonderful website where you can plug in the Latin name of over 700 different plants and it will show you in-depth information, including native range, the site conditions species are adapted to, how to propagate, and more.
So there you have it: the happy news that there is indeed room for a few well-chosen exotics in a garden that supports wildlife. And you have a number of great resources to explore, too.
But before saying ‘bye for now, I’d love to hear from you!
If you’re interested in increasing the number of natives in your garden but are overwhelmed by the amount of information out there, what would make it easier for you?