Does not tolerate waterlogged soils. At publication time, no infestations are known to exist in California. Plants previously eradicated occurred in Modoc, Siskiyou, and Mendocino cos. Scattered throughout most of the U.S. and Canada. Seeds that mature early in a season typically produce biennial plants.
Seeds maturing late in a season often produce annual plants.
Newly matured seeds germinate without light. Seeds that become dormant germinate best when exposed to light. Biennial seedlings require a cold moist period to induce stem elongation and flowering. In colder, more northern regions the proportion of annual plants is higher than in more southern clines. Prevent seed production by cultivation, hand pulling, or mowing plants.