If you have an infestation of valerian, the earlier you get it under control, the better. Valerian is a prolific self-seeder. The seeds are viable for two years or less, which is not overly long compared to other invasive species whose seeds remain dormant in the soil for many years but its seeds are powdery and spread easily by wind. The plant also spreads aggressively by its rhizomes. Valerian emerges early in the spring so it often has a head start over native plants that break their dormancy later. Native plants might not be able to compete for nutrients, water, and sunlight in a location that valerian has already occupied with its vigorous growth.
How Does Valerian Look Like
Valerian has dark green, pointed, toothed leaves with a hairy underside. The thick and hairy stems are hollow and support sweet-smelling white or pale pink flowers with five petals that appear between June and August. The flowers are tiny and form tight, dense, umbrella-like clusters. After they bloom, the flowers turn into oblong capsules containing numerous powdery seeds. The outstanding characteristic of valerian roots is their pungent smell. It is somewhere between earthy and foul and funky, often compared to the odor of dirty socks.
How to Get Rid of Valerian
If there are just a few valerian plants popping up in your yard, remove them by hand. This is best done by lifting them out of the ground with a trowel to make sure you get the entire plant—the stem breaks easily—as well as the roots. Do this as soon as the seedlings emerge, and definitely before they flower and set seed. If valerian has overgrown a larger area, you can mow it. Again, this needs to be done before the plants set seed. If you are too late, mowing or any other form of mechanical removal will make it worse because you will just spread the seeds around further. A heavy infestation might require repeated mowing and a follow-up spray treatment with an herbicide containing glyphosate. Keep in mind, however, that this is a non-selective herbicide that kills all other vegetation around it. Whichever removal method you choose, it is important to monitor the area carefully afterwards in order to get rid of newly emerging plants promptly before they set seed.
