Hoary cress (Cardaria draba) is an invasive perennial herb. It grows up to 0.6 m tall. The seed pods look like inflated, upside down hearts. Each seed pod contains two reddish brown seeds. The seeds are viable for up to three years. It can produce 2 crops of seed per year. It has white flowers that grow in dense clusters. It has a flat-topped appearance early in the season and is sometimes called white top. The lower leaves are hairy and have stalks that attach them to the stem while the upper leaves are hairless and clasp the stem. The leaves are shaped like arrowheads, are alternately arranged on the stem and have finely toothed edges. It has a single stem that is often branched near the top.
It has a rhizomatic root system. Hoary cress spreads by both seed and roots. The roots spread and create dense patches of clones that can cover an area of 3.6 m. The root system comprises over 75% of the plants total biomass. The roots can spread for 9 m.
It is native to Eurasia and it most likely came here as a contaminant in alfalfa seed. It very important to ask for the seed analysis certificate when you buy seed. Hoary cress grows in meadows, grasslands fields, roadsides, ditches, along waterways and rangelands. It is particularly adapted to sub-irrigated alkaline soils. It is an early bloomer and easily create a dense monoculture that out-competes native plants. It is generally unpalatable to wildlife and livestock.
Mowing 2-3 times a year for several years may slow the spread and reduce seed production. Mowing should be conducted before it flowers and repeated before the second flowering stage. Selective herbicides are an effective form of control. Seeding helps to create completion and is an important part of treating invasive plants. Because of its extensive root system pulling is not very effective.
For more information on invasive plants please contact the Boundary Invasive Species Society at 250-446-2232, firstname.lastname@example.org, www.boundaryinvasives.com and on Facebook.