Answer: Sedum may be divided in early fall or spring; you may also make tip cuttings in the spring -- they root easily.
Once foxglove has set seed and it has dropped, you may cut back the tall flowering stems close to the basal foliage. If you do not want them to self seed you may cut them back sooner.
You may wish to cut back both black eyed Susans (rudbeckia) and purple coneflowers (echinacea) after bloom has finished; some gardeners also deadhead them or trim off the spent flowers as the season progresses. (This may extend the blooms season.) However, some gardeners leave the seed heads intact so that the birds may feed on them and to allow the plants to self sow. Some people also find the seed heads a nice interesting addition to the winter garden. If left on the plant over winter, they should be trimmed away in early spring.
It's really a matter of personal preference. Enjoy your flowers!
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