Posted: 05/10/2013 at 08:24
Agastaches have flowered since early June.....black adder for example,
Astrantia jumble hole has never been out of flower. Astrantia Roma is in its third bout of flowerimg.
Lychnis coronaria is cut back hard in early September and that makes it flower now until late autumn or beyond.
Heleniums, dahlias, and many others flower for a very long period.
For very lomg flowerimg I recommend a salvia.....check out Amistad. This is a glorious plant. Purple surrounding black on vigorous 4' plus plants and it has flowered from,late spring.