As spring transitions to summer and our gardens are in full bloom, it is a good time to take stock and make sure you aren’t accidently growing some of Oregon’s worst invasive species! Invasive species can sometimes seduce and fool you with their beautiful and showy flowers. Unfortunately, these pretty invasives can distribute thousands or even millions of seeds each year that find they’re way into our water systems and wetlands. We invite you to walk your yard, or neighborhood, and see if any of these invasives are finding a home where they shouldn’t be! Removing these plants allows native plants a greater chance to thrive both in your yard and community at large.
Scotch Broom: Scotch Broom is the bright yellow flowering bush that you see along roads and waterways or maybe in your front yard. It is a very aggressive plant that can take over if it is not controlled. You can identify it by its yellow pea flowers that turn to black seedpods. To remove plants less than three feet tall, pull up the roots. For larger plants, cut the stems near the ground, however up to half of them may re-grow from the cut stumps, so follow-up treatments of cutting may be necessary. The best time to remove, cut, or pull the plants is before the seeds begin to disperse in July to September. Mature plants can produce 300 seeds per bush and seeds persist in the soil for up to 80 years!
Purple Loosestrife: The beautiful showy pink flowers make this a garden favorite. A single mature plant can produce as many as two to three million seeds a year. If you have this plant in your garden please remove it as it is an aggressive invader of marshes. When purple loosestrife takes hold, it forms dense, impenetrable stands which are unsuitable as cover, food, or nesting sites for a wide range of native wetland animals including ducks, geese, rails, bitterns, muskrats, frogs, toads, and turtles. You can identify it by is square wood stem and opposite leaves and of course magenta flowers. Loosestrife can produce from root fragments so make sure to remove the whole root system. Pull plants before seed set so you stop the distribution of all those seeds!
Yellow Flag Iris: This tall, yellow iris loves wet and muddy places, like the area beneath your hose or places where water collects. Yellow flag invasion is a major problem in Oregon’s wetlands and extremely difficult to remove and control. Another one of those beautiful plants that spice up a garden, that can have serious negative impacts on wetlands. This iris can regenerate from the smallest amount left behind, so be sure to dig deep with your shovel and remove the whole plant. When finished, make sure to dispose of the plant in a container as left out the plant may regrow.
Knotweed: It might look like bamboo or a Jack in the beanstalk like plant but it is not! Knotweed loves stream banks and wetlands but it also might love your backyard. It can grow up to 12 feet tall and has pretty white flowers in the early summer. This plant is powerful, even the smallest piece can take root so it is important to remove as much of the root as possible, discard in the trash and do not compost. You will likely need to repeat this process several times. Another control method is solarization, cutting the plant at ground level and cover the remaining stem with a heavy dark cloth or plastic. Keep the plant covered until you can easily pull it out of the ground, this will likely take several months.