I have never seen a list of day-length preferences of plants, but if I were looking for one I'd try the Brooklyn Botanic Garden or maybe good old Arnold Arboretum's library.

The day length characteristic is really interesting, though; even if we don't have as much heat and strong sun as other regions, we DO have the same day length as elsewhere at this latitude. Do you think that in plants that are sensitive to day length, the strength of the sun might be a completely different characteristic, or are you saying that you think they're linked?

I think some plants just need more sun and heat than we normally get - like my favorite Salvia, S. leucantha, the Mexican bush sage.

One more thing - although I don't have much luck with hardy Delphinium (I won't dignify them by calling them perennials) the annual larkspur (which IS a Delphinium) does just fine here. So, I don't think Delphinium's known failure to grow in these parts necessarily has anything to do with day length. It may be the case with some other plants, of course.

Katy,

The short- and long-day response to which you are referring is called the photoperiod of plants. You can probably google it and get a much better explanation than I can give you. But the plants respond to light vs. dark as far as determining setting buds, going into or breaking dormancy and so forth. The strength, or hours of actual sunshine (or the lack thereof) really don't influence the plants ability to set buds for example. However, some plants will just grow faster and healthier with warm, sunny dry days, so long as the soil is moist enough of course. Having said that, you may well see an abundance of blooms when there is ample sunshine. But there are two separate things here. I hope I didn't confuse the issue!

Bill