Weed Watch: What are those tiny white flowers blooming in my lawn?

By Mary Free, Extension Master Gardener

If you have been out and about enjoying the warmer weather, then you may have noticed, especially in shady areas where the soil is moist, scattered clusters of tiny, white, 4-petaled flowers with 4–6 stamens. They sit atop thin, 4–10-inch stems that rise from persistent basal rosettes. The leaves forming the rosettes are simple-pinnate with 5–7 alternately arranged, rounded leaflets and their presence during flowering distinguish this non-native hairy bittercress (Cardamine hirsuta) from native Pennsylvania bittercress (Cardamine pensylvanica), which has few to no basal leaves while in bloom. Its common name and epithet (hirsuta) refer to the sparse hairs on its leaves.

This winter annual weed is one of the first to bloom in spring and its flowers provide early season nectar to bees and butterflies. Although hairy bittercress usually dies back as the temperatures rise, it can persist year round in favorable conditions. As the long slender fruits called siliques ripen, their tissues swell increasing internal pressure to a point at which they explode dispersing seeds (hundreds per plant) potentially up to a distance of 16 feet. This type of forceful seed ejection is called ballistichory, ballistochory, or ballochory. The seeds can remain viable for several years and are often transferred from nursery pots to home gardens.

Cardamine hirsuta (hairy bittercress) plants easily pulled out of moist ground on March 29, 2021 show their fibrous roots. Photo © Mary Free

A healthy, dense turf and mulched gardens will help prevent hairy bittercress from spreading. Herbicide use should be a last resort, but if needed, heavy infestations are best treated in the fall (see Broadleaf Weed Control Chart). In the spring, control is important. Frequent mowing to remove flower stems will prevent the weeds from reproducing. Luckily hairy bittercress’ shallow root system also allows for easy hand-weeding, especially if the ground has been softened by rain. Remove the plants in early spring before the siliques ripen, but do not compost them if in flower as they could set seed. Once you remove the weeds, you may want to save some leaves for the dining table.

Edible, sparsely hirsute, basal leaves of Cardamine hirsuta (hairy bittercress). Photo © Mary Free

Besides being food for pollinators, bittercress is edible. Unlike its name, its taste is more peppery than bitter. Use it in place of parsley or add some fresh sprigs of the micro greens to salad, soup, salsa, and pesto. They are nutritious raw or cooked, just be sure that they have not been exposed to herbicides or pesticides before eating them. Flowers also are edible but chewy.

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