Common St. Johnswort, a wildflower, likes full sun. So does Shrubby St.
Johnswort, also a wildflower.
They are generally field plants.
There's a whole chapter on the natural history, folklore, medicinal uses,
horticulture, etc., of St. Johnsworth in a new book called The Secrets of
Wildflowers.
See http://www.acorn-online.com/hedge/secrets.htm
Good luck!
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Jack Sanders 91 Olmstead Lane
Ridgefield, Connecticut 06877