I don't have experience with it, but Betsy Clebsch doesn't mention flopping in her description of this plant. She does say it prefers light to medium shade with regular watering, but it will tolerate full sun with more water and "protection of other plants."

Brenda

The deeply quadrangular ridged stems have sturdy nodes, leading me to believe it evolved to have pretty good wind resistance. The young stems are much more flexible and can flop.

I have Betsy's book but sometimes Texas weather is not really considered in gardening advice publications. We get as high at 110 in the summer. I have irrigation and will try to give it morning sun with partial shade in afternoon. Perhaps near some tall Dallas Blue Switchgrass...anyone from Dallas plant this guy?

I'm in Dallas and have grown this for a number of years. It doesn't flop, and I grow it in full sun with no shade.

How did yours do this summer? Hope it did well and you are enjoying the blooms!

Wow...this was and old post. Since then I had two successful season near White Rock. Last Fall we moved to north Dallas and I took a clump which is blooming right now! Love this plant! Soft butter yellow. Tall spikes. SMF, let me know if you ever want to trade since we're in the same zone.

smf & Dallasgarden:
Mine is blooming right now along w/S.purpurea & elegans.
glad to hear it made it through the winter.Mine is still fairly new. I have seen S.madrensis in sun here also.
plants can get to be 5-6' wide. Growing by underground runners. You climate may reduce that.
Art

I grew mine in rich dirt in Austin in shade with morning sun. I am now on a cistern so not a whole bunch of watering, and it is on on very porous calcarious soil and I have it under an oak tree . It is just starting to bloom now. I dump compost on it every year. My soil is VERY SHALLOW and I watered it once this year. Me bad. It grows a lot shorter out here and liked it better in the old house.

mine is flowering here, it is very rigid. Cant really imagine it limpy and falling over. Mine is in full sun to 3/4 sun. It gets water every 3 days or so. More when it is in the upper 90's (currently) and 100's. But does very well. All of my winter perennials are budding as we speak. wagneriana, purpurea, gesneriiflora, holwayi, no karwinskii yet. Mine also has a few macrophylla's in front of it though.

I live in Plano and have a very healthy specimen growing in half day full sun and then filtered shade on the edge of a Pecan grove. It is very sturdy and does not flop. My soil is heavy clay with lots of manure and compost worked in.