This is the blazing star most commonly found in catalogs.
Its been bred to grow 1.5 to 3 feet tall, much shorter than
the wild version (at left, in the Bunker Hill Prairie
of the Cook County Forest Preserves) which goes up to 6.5
feet. Catalogs typically offer white and purple versions.
Despite the fact that its called marsh blazing star, a lot
of water will encourage the bulb-like roots to rot, at least
in Chicago soil. These plants do extremely well in the Cook
County forest preserves where of course no one waters them
at all. They can get mildew so arrange for them to be in a
sunny location where there is good air circulation. Bloom time
here is July although the taller wild ones bloom in August.
No one yet has claimed that cutting back or deadheading will
produce more flowers.
Letting them go to seed is a good idea, it will give you a source of new plants to make up for any that rot. Goldfinches will also eat the seeds. The wild ones (at least) are supposed to need 120 days of cold treatment so just let the seeds fall where they may. They will not bloom the first year. If you have a mixture of white and purple plants then almost all of the new plants will be purple. Plant the bulb-like roots with their tops at or very near the soil line.