Sadly, many of us have come to think of the plants in our yards as ornaments. In the process, we've unintentionally turned our home landscapes into something that, biologically speaking, sometimes resembles the surface of Mars. That is, barren and sterile.
What’s more, as is the case with the lovely butterfly bush, your plants may actually be damaging the biodiversity in your neighborhood. But when we plant trees, shrubs, flowers, and grasses that are meant to be there (versus introduced species by way of the ornamental-plant industry), this helps the bugs that have evolved to rely on them.
Which, in turn, helps all of us, explains Doug Tallamy, PhD, professor and chairman of entomology and wildlife ecology at the University of Delaware in Newark. "We humans don't need the bugs for food, for example," says Tallamy. "But we do need them to help run the ecosystem. And an ecosystem with lots of species is more stable." Tallamy, author of the popular book, Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, says that "native plants are the basis for ecosystem services we absolutely need, such as oxygen production, pollination, moderation of our weather, cleaning our water, and sequestering carbon dioxide."
With all that in mind, maybe it won’t be so hard to pitch the pansies and problematic plants in exchange for, say, a Monarch butterfly–supporting milkweed. Or a native oak tree that can support 534 species of butterflies and moths. Talk about a bang for your biodiversity buck!
THE DETAILS: Because plants don't like being eaten, they produce chemicals that deter bugs. But insects have evolved such that they can tolerate certain plants, and rely on them for survival. In fact, 90 percent of the insects that eat plants have become specialized in this way. For example, some have developed enzymes that help them live off of a particular plant, explains Tallamy. Monarch butterfly larvae have adapted so they can eat milkweed plants. But when these and other native-born plants are replaced with turf lawns and exotic ornamentals, and natural areas get bulldozed and replaced with nonnative species, there’s no food left for the butterfly larvae.
Okay, if you don’t have a soft spot for insects, maybe you do for birds. When you start taking insect species out of your yard thanks to your nonnative plant choices, birds suffer as well. "Birds don't eat plants, but when they are reproducing, they’re eating insects almost exclusively," explains Tallamy. "When you take insects out of the local food web, you remove food for birds, lizards, frogs, salamanders, bats, and even foxes and black bears. Bugs typically make up almost a quarter of a black bear's diet. In other words, the food web can collapse when you add too many plants that insects can't eat."
WHAT IT MEANS: Tallamy says 41 percent of our land is in agriculture (most of it chemical agriculture, which comes with its own human health and environmental liabilities ), and 54 percent is suburbs and cities. Therefore, when we plant nonnative species in populated areas, we’re profoundly affecting the biodiversity of half the country.
For example, 85 percent of the invasive woody plants that strangle out native plants and wreck biodiversity are escapees from our gardens, says Tallamy. The problem is so acute in some areas that last year, Oregon banned the sale of English ivy. (Unfortunately, many Oregon state parks have already been decimated by this climbing, smothering vine.) You can still buy certain invasive plants, such as miscanthus, and invasive ornamental grasses as well, Tallamy says. Which is why it's so important to know what's environmentally friendly and what isn't before you head to the nursery or garden center.
Here are some tips for making your yard a natural paradise:
• Find out what's native to your state. What works in some states could be a problem in others. To determine which plants are native to your area, visit Wildflower.org for commercially available native plants. Or search for native-plant nurseries in your area. Then ask at the nursery for help choosing the right plants for your yard.
• Plant them in clusters. Tallamy recommends planting bunches of the same native plants for two reasons: It provides a better visual display, and if insects do come (a good thing), it’s less likely they’ll wipe out your offerings if there’s more than one of them. "Also, go for the biggest diversity you can manage," says Tallamy. "Think in terms of plant communities rather than specimen plants. That's the key. That’s the way it would be in nature."
• Cut back your garden wisely. Native wildflower gardens and meadows literally hum with life during the blooming months, but they serve important roles during cooler months as well. "A lot of people create wild, meadowlike areas in their yards, and they want to mow it all down at the end of summer,” says Tallamy. "But all of those plants produce seeds, and birds need seeds all year long. For example, goldfinches love wildflower seeds, and they’ll lose out if you mow down the flowers after the blooming season. Also, some insects like lay eggs in the stalks of plants, but if the stalk isn’t there, they can’t do that." Tallamy suggests that if you want to cut back plants in the winter, just do it to a third of them, so nature’s creatures can benefit from the remaining two-thirds.
• Take out problematic plants. The most invasive weeds—those that choke out plants, trees, and take over forests—do damage to this country’s biodiversity. And that's a problem for all of us. (The more species that thrive, the healthier the ecosystem.) Example: When the invasive plant called purple loosestrife, once sold by the ornamental-plant industry, invades marshlands, it actually can drop the water table and largely destroy this important ecosystem. Try to rid your property of all invasive-type plants.
• Enjoy the show! Migratory birds tend to fly at night until they reach a point of exhaustion just before dawn. At which point they descend to the ground in search of shelter and food to fuel up for their long journeys. "Once they hit the ground, they've got to find food right away," says Tallamy. "If there’s no food, they can die pretty quickly." So, by having native plants in your yard, along with the insects they’ll attract, you may attract migratory birds and butterflies you’ve never seen. Add that to the reasons for having native plants in your yard!