Editor’s Note: This is the second in a series of five articles for April, Native Plant Appreciation Month, on the importance of landscaping native plants in the Snohomish County garden.
Many people think of native plants as a kind of granola that you would like to have. In fact, they are vital to our environmental health.
To understand why, we must start with insects. As mentioned in last week’s article, they are the key players holding the environmental web together. We see a good example of this in our birds. While most songbirds get their food from seeds, berries, and birdhouses, they depend on insects for the high-protein food they need to nest and raise their young. Caterpillars are a particularly important food source.
What does this have to do with native plants? Around 90% of herbivorous insects are specialists. This means that they depend on one or maybe a few plant species for survival. The classic example of this is the monarch butterfly, which depends on the milkweed plant for food during its caterpillar stage. The eradication of spurge has led to a 96% decline in monarch butterflies.
Why do so many insects specialize? It all boils down to the fact that plants don’t like to be eaten. To protect themselves, they use a wide range of toxins and other repellents. Insects and other herbivores have evolved ways to overcome these defenses over many thousands of years. Spurge, for example, owes its name to the sticky white sap that is excreted from its leaves. The sap sticks the mouths of would-be insect predators. Monarch caterpillars have learned to circumvent this by notching the main vein of the leaf, allowing the sap to drain before eating the rest of the leaf. Spurge also produces potent toxins that stop most insects. Monarchs have evolved enzymes to reduce the effects of these toxins. They have even learned to hijack the milkweed’s defenses by storing the toxins in their wings, which helps them fend off their enemies.
Although monarchs and milkweeds are not native to the Northwest, many similar, interdependent relationships can be found among species native to our area.
Non-native plants have an unfair advantage over native plants. In their new environment, they lack the insects and other predators that have taken thousands of years to learn to overcome their defenses. Without natural predators, they reproduce and replace native plants in our open spaces, highway edges and nature reserves. When this happens, insect populations, especially caterpillars, decline and as a result, our songbirds disappear. The decline in bird populations is cascading through the food web, affecting raptors and other higher-ranking predators. Examples of aggressive non-native plants in our area include English ivy, evergreen and Himalayan blackberries, and English holly.
Native plants interact in ways we are just beginning to understand. An example of this was discovered in British Columbia when investigating why Douglas firs became diseased after their birch neighbors were removed. It was discovered that the trees exchanged nutrients back and forth between their root systems through the soil fungal connections. This arrangement worked because it benefited both tree species. Non-native plants lack such connections because they take many thousands of years to develop.
Of course, native plants nourish and protect our environment in many ways. That’s not to say that everyone should be expected to completely uproot an existing landscape to replace it with natives. Instead, consider natives whenever adding or replacing plants or as a way to enhance your existing landscaping.
When choosing plant species, consider site conditions, including sun exposure, soil moisture and texture, slope, drainage, and space. With this information, you can take full advantage of the expert resources available to assist you in your plant selection. It is important to identify plant species that will thrive in the conditions your site offers. Our native flowering currant is a favorite that tolerates a wide range of conditions. It is prized for its early spring color and prized by our native Anna’s hummingbirds as a source of nectar at a time of year when other options are less plentiful.
Sites to Explore
For more information on native plants, visit the Washington Native Plant Society’s website at www.wnps.org. From their website you can link to our local WNPS Salal chapter, www.wnps.org/salal.
The National Audubon Society also has information on bird-friendly gardens and a directory of native plants that you may find useful (www.audubon.org/PLANTSFORBIRDS). Plus, their “Plant for Birds” sign can help start conversations with neighbors about animal-friendly gardens (tinyurl.com/EDH-audubon).
If you want to see the native plantings firsthand, consider visiting the Edmonds Wildlife Habitat & Native Plant Demonstration Garden, sponsored by the Pilchuck Audubon Society, our local chapter of the National Audubon Society (www.pilchuckaudubon.org/edmonds- wildlife-habitat – native plants demonstration garden). It is located at 95 Pine St. in Edmonds. You can also visit the Salal Native Plant Garden, a collaboration between the Salal Chapter of the Washington Native Plant Society and the Washington State University Agriculture Extension. It is located at 16650 State Route 536 in Mount Vernon (www.wnps.org/salal-programs/garden).
Snohomish County Public Works maintains a list of nurseries in Snohomish, King, and Skagit counties that have native plants for sale: tinyurl.com/EDH-nurseries.
Next week’s article examines how your garden’s soil plays a key role in your landscape’s environmental productivity. We will discuss the numerous benefits of a natural approach to maintaining soil health.
William McClain of Lynnwood is a member of the Pilchuck Audobon Society. The Washington native published his first novel, The Risk in Crossing Borders, in 2020 after retiring from a career in benefits counseling. He hopes to publish a second novel in 2023, set in England during World War II. His interests include hiking, nature photography and playing soccer.