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.

Summer days are shorter, but winter days are longer. It is much more dramatically noticable near the poles and equator.

Looking for the one perfect onion, huh? :-) Seriously, what is your primary goal? Flavor? Only non-sweet? Bulb size? Saving seeds while still having edible onions? Experimentation and pushing the envelope? Etc.? There are easy answers for each one of those but sadly there is no one perfect onion variety that could even come close to perfect for all those goals. Don't we wish! Seed saving for onions is a total waste of time IMO simply because the seeds have such a short life span/viability without expensive ideal storage conditions and even then it is still short. Plus, even when viable, yes there are health, sterility, and production issues with F1 seeds unless they are crossed under ideal conditions. Flavor is as much a product of the growing conditions you provide - soil pH, consistent soil moisture levels, consistent nutrient levels, spacing, planting/harvesting date, proper planting depth (bulbs form above ground), etc. - as it is of the variety. So be sure to re-evaluate all those factors too. Bulb size is exclusively a result of growing the proper day length so unless we want to move or invest in high pressure floodlights, we are stuck (so to speak). But we can make some trade offs - accept smaller bulbs to grow some of the long-day varieties (just grow more of them), change planting dates drastically and protect if necessary, and do everything we can to insure proper growing conditions soil and water wise. Several have mentioned all the great info available at Dixondale Farms in Carrizo Springs, Texas so if you haven't explored all the info they offer please do so. Dave

To complicate matters, not all long day varieties are adapted to the same latitudes. For instance long day Walla Walla is adapted from latitudes 35-55N so I can grow it here in KC at 38.5N but long day Redwing is adapted from 43-65N so I can't grow it because it needs longer days then I get (just under 15 hours) here to bulb up properly. Johnny's Selected Seeds website lists the latitude adaptation of most of the bulbing onions that they offer which should help you select some that would do well in Wichita. Here in KC, I've grown Candy, Red Candy, Superstar (now named Sierra Blanca), Walla Walla, Copra, and Red Defender. Of those, Copra is supposed to store the longest.