Phacelia

Phacelia is an cool-season, fast growing annual broad leaf plant used for soil improvement that does not make Nitrogen, but scavenges and stores it for a proceeding crop.
Phacelia provides a dense cover that easily allows water infiltration, making it an excellent weed suppressant.
Phacelia is an excellent bee attractant with purple flowers.

Phacelia has a prostrate growth habit and can get up to 3 feet tall and needs 13 hours of daylight to begin flowering.
Phacelia will germinate at temperatures above 37° and winterkills at temperatures 18° or below.