Sympathies from a fellow perennial gardener, Loretta. Had so many problems with the survivability of so many herbaceous perennial cultivars, myself.
Over the years, have planted the species Gaura lindheimeri in several gardens; it never came back the following year in any of them. On the other hand, there's a garden around here that has had it, in a sunny, uncrowded, position, for a number of years. A case of the plant telling the gardener where it should have been planted?
Re Coreopsis: have planted it over many years in a number of gardens. The only cultivars that just went on and on (including reseeding), year-ofter- year, were older ones ( like 'Sterntaler').
I'd assume that the older perennial cultivars, sold here 20 or 30 years ago, were generally more vigorous than those sold now. There's been subsequent horticultural selection for things like more showiness, smaller size, less height and tameness (viz. not running or seeding). I really appreciate the last mentioned; however, it likely means weaker plants.
I'd take it that (herbaceous) perennial gardening can be much more of a challenge than gardening with annuals, requiring more observation, experience, knowledge and labour. It sometimes has seemed, to me, that the kind of perennial garden I envisage, should be completely replanted every five years. It would look: a bit depleted in the first year: better in the second: at it's prime in the third: getting a bit untidy in the fourth: and needing replanting in the fifth.
