Vervain- Hoary (Verbena stricta)
Livestock will not eat Verbena so it may be thought of as "weedy" by some who observe it in a pasture setting. In a natural prairie it is not aggressive. In fact, it is a rather short-lived perennial that will not compete well with more aggressive vegetation. It self-seeds readily and is very easy to germinate, so it is a common component of many drier prairie seed mixes.
Sun Exposure - Full, Partial
Soil Moisture - Medium-Dry, Dry
Height - 2 feet
Bloom Time - June, July, August, September
Bloom Color - Blue
Photo courtesy of Prairie Moon Nursery.