I would like to know a little more about Verbascums. Are they a biennial? Will they reseed themselves? How long a period will they bloom. How tall can they become? Are they invasive? Thank you for you help! I have had very little experience with annuals and biennials.
Verbascum includes 360 species, most of which are biennials, with a few annuals, perennials, and small shrubs, some of which are evergreen or semi-evergreen. The flowers grow on tall upright stems, and while individual flowers are shortlived, there are many of them and they bloom over a long period of time (summer into early fall, in most Seattle gardens).
In my own experience, they can reseed themselves, so if you would prefer not to have your plants do this, just cut off the tall stalk after the flowers have bloomed, and before they set seed. I checked the list of Washington State Noxious Weeds, and did not find Verbascum there, though it can be invasive in other parts of the country (Hawaii, for example).
If you would like information about specific varieties of Verbascum, the Royal Horticultural Society A-Z Encyclopedia of Garden Plants has photographs and descriptions of many of them.