Make Wise Garden Choices to Help Control Invasive Plants

Seth Cool is the program coordinator for the Washington Invasive Species Coalition.

Whether you’ve battled dandelions or herb Robert in your backyard, pulled ivy from your trees or seen trees along roadsides engulfed by clematis vines, you’ve undoubtedly noticed the spread of invasive plants. Half of the plants on the state noxious weed list are garden escapees, so making wise garden choices is an excellent step in controlling invasive plants.

One way gardeners and landscapers can help is by choosing non-invasive plants for their yard. For almost every invasive plant, there are good alternatives that provide the same features, minus the invasive side effects. A new booklet published by the Washington Invasive Species Coalition, with the help of others, entitled “Garden Wise,” features 17 invasive plants and recommends at least three alternative plants for each.

For example, yellow flag iris is an invasive plant, which spreads, creating dense mats that disrupt water flow in wetlands and streams. Fortunately, there are many other irises with beautiful foliage and flowers, and are easy to grow, but not invasive. Laevigata iris (Iris laevigata) is a beautiful water-loving iris. Siberian iris (Iris sibirica) is suitable for damp and drier sites and has flowers ranging from yellow to purple.

Old man’s beard (Clematis vitalba) and silverlace vine (Polygonum albertii) are aggressive climbing plants, which produce seeds that spread in the wind and on the bodies of birds. Both are considered invasive because they take hold in natural areas and smother trees, shrubs and fences. A choice recommended by the Washington Invasive Species Coalition is Italian clematis (Clematis viticella), which comes in a variety of colorful cultivars and grows up to 15 feet tall. Orange honeysuckle (Lonicera ciliosa) is another safe alternative, and a favorite of mine. This native climber grows slowly, but rewards gardeners, birds and butterflies with vibrant orange flowers.

The invasive plant problem goes much deeper than just creating problems in the garden. The most devastating impacts occur when invasive species spread to wild areas and crowd out native plants, which are not only important in their own right, but also provide food and habitat for wildlife. For example, salmon have evolved to depend upon bugs that feed on leaves, fruits and flowers of native plants. Recent studies found that Japanese knotweed replaces native riverside alder and cottonwood forests. It returns less nitrogen through fallen leaves into streams than natives, providing less food for aquatic bugs that salmon eat. (By the way, if you’re looking to replace that knotweed on your property, alternatives are covered on pages 8-9 of “Garden Wise.”)

Invasive plants already choke 3.6 million acres of our national forests (an area the size of Connecticut), and invasives advance by 1.7 million acres annually (an area two-thirds larger than the state of Delaware). The combined annual cost of invasive species to the U.S. economy is a staggering $138 billion. For example, European purple loosestrife costs an estimated $45 million annually in control efforts and forage losses.

The invasive problem is so serious that Washington state has recently created a statewide invasive species council which will coordinate efforts to prevent and control invasive species in our state. While many damaging plants are illegal, many are still sold or traded by gardeners.

The good news is that only a handful of garden plants are invasive, and there are often many exotic and native plant alternatives to choose from. I encourage you to have a look at the booklet on the Washington Invasive Species Coalition Web site (http://www.invasivespeciescoalition.org) and when buying plants to ask the nursery if the plant is invasive.

The Washington Invasive Species Coalition is a coalition of conservation groups and educators working to stop the introduction of invasive species in Washington state. One of their projects is focused on stopping the introduction of known invasive plants. They’re working in conjunction with several nursery owners to phase out the sale of invasive plants and to promote safe plant choices. §