Q.Why Won’t My Moonflower Blooms Open Completely?
This is my first year growing moonflowers. It’s August 1st in MS so smack in the middle of the usual hot as Satan’s armpit summer. We’ve had delightful clouds and much lower temps the last 2 days though. Highs only low 80’s and lows in upper 60’s last night and tonight. The vine has done great in the ground climbing up a back porch post – about 15′ tall and still climbing – with many flower buds set. I had to throw up additional homemade/make shift lattice 7 days ago at the top of the post, asking the vine to make a horizontal turn, because it was growing onto the roof of the house. It’s already covered 3′ of the temp support, and I feel sure I’ll be adding on and making notes for next season. The first 2 flowers just bloomed (started about 5:15 pm thanks to the clouds) but they didn’t open all the way. They got about 1/2 way open then stopped. My vine is mostly west facing so it’s usually still bright daylight until about 7:00-7:30 when the sun starts sinking behind a tree line in the distance. I’m wondering if perhaps the future blooms will open fully once the temps drop consistenly? Did it open too early in the evening, confused by the cloudiness and cooler temps after so many many sunny days with temps consistently in the low to mid 90’s and heat indexes of 100+? I’ve been counting the days awaiting these beauties, and while even the 1/2 open blooms are gorgeous and fun to watch (time lapse video running as we speak), I’d love to have the full show with completely open blooms. Any guidance, tips, knowledge is greatly appreciated.

Certified GKH Gardening Expert
Many times, blooms will only last through one night. They will fall off by morning, typically.
If you know for a fact that they are not opening fully overnight, then there is a high probability that there is too much nitrogen in the soil.
A soil test will confirm, but this can be offset by adding potassium and phosphorus.
Here are some articles that will help:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/ornamental/vines/moonflower/growing-moonflowers.htm