Follow Up: I think my experiment may have already mostly done itself due to the run of 104-to-106-degree days we just had. I'll explain the pictures, but it seems that my daylilies really do need supplemental shade to avoid stress and perform at their best in my 9b garden. The sun is direct on my "blast furnace" garden from about 8 am to 4 pm, so they get 8 hours of full sun, with an additional 4 hours of indirect rising or setting sunlight (mostly blocked by neighboring houses and 6-foot privacy fences).
Potted and trimmed daylilies in shade did great even with soil that quickly dried out, perhaps because the shade reduces temps by about 20 degrees (down to 85-90), and sun exposure by 50% or more from lattice on the roof and sides of the patio. Those planted in-ground in the deep shade garden, and between two shading bushes, also fared well without or without trimmed foliage.
But, the untrimmed fans in the blast furnace garden did not seem happy at 106 with no shade. And, like Sooby mentioned, trimming might have left them even less able to withstand the heat and sun.
All plants receive approximately the same amount of watering, with an extra pass given to the 106/blast furnace garden. That soil stays just this side of moist, with a finger poke that tells me there is cooler, well drained soil under dry topsoil. If I'd trimmed foliage, the browning and curling-up of leaf blades would perhaps have just gone even deeper in toward the crown. But, leaving them uncut and exposed to full sun for eight hours is still putting them under much more stress than plants 30 feet away that enjoy the shade of patio, bushes, or trees.
Potted, trimmed plants at the side of the patio, temp reduced to approx. 85-90 degrees by 50% shade provided
Potted, trimmed plants on the patio under latticework, temp reduced to approx. 85-90 degrees by 50% shade provided
In ground, trimmed plants flanked by bushes on either side, temp reduced to approx. 85-90 degrees by 50% of shaded provided
In ground, untrimmed plants shaded by trees and buildings, temp reduced to approx. 85-90 degrees with 80% or more shade
In ground, untrimmed plants in blast furnace garden, 106 degrees and unshaded during eight hours of full sun. Pinks, Carnations, Sea Thrift and Cactus all stayed fully green.
Thanks for letting me try this out. I can tell now that trimming foliage (or not) will provide little or no protection for my full sun daylilies. I can also see that providing them with 50% shade cloth coverage, as soon as temps go above 90-100 degrees, might help them avoid the stress of heat dormancy. I'll work on setting up a retractable clothes line, strung with shade cloth, to pull over them for next summer. As always, though, if anyone has cautions or thoughts about other ways to provide them protection from full sun, I'd be interested in hearing about it. However, planting trees or bushes in the blast furnace beds is not an option for me - so that alternative solution would not be possible in this case.
