I am also in Oklahoma, and mine are doing the same thing! I have tried everything you have, and still, they die off before they open...

Would it be poor soil??

I've wondered if my soil is too good! lol The moonvine are planted in my front porch flower bed that produces everything else beautifully. The vines are healthy with large, prolific leaves. They have an eastern exposure..Maybe not enough sun? My newest plan of attack is to water in the morning instead of the evening. How odd yours are doing the same thing. It's like they just don't have enough oomph to open.

I thought maybe it is just the OK heat! I have some new ones coming into bloom, so I will watch them and see what happens. We put down an extra layer of mulch too, you can never have enough mulch!

I planted my moonvine because we are getting married in our back yard at sundown in a few days, and I was hoping that they would be blooming during the ceremony.. but I don't think that is going to happen.. Great vines though, heart shaped, perfect for a wedding.. :)

I have a beautiful vine this year, full of buds.
They have been trying to open for 2 weeks, but not one has managed to open yet. The bud gets full and looks like tonight is the night, but it never completely opens.
I have had Harlequin bugs for the first time this year on my cleome, they have now moved to the moonflowers, wondered if this might cause the problem?

I am having the same problem with my moonflowers--the buds are large and I keep waiting for them to open and then I see the unopened buds on the deck the next day. I have only had two flowers to open this year. The weather had been unusually hot for a Michigan summer but now it's unseasonably cool.
If anyone can help--please advise.
Thank you

Hallaleuah!!! Misspelled but you'll under stand the sentiment! Finally! Moonflowers are opening! Our nighttime tempature has dropped below 80 and the vines are full of beautiful flowers!

Mine are doing better with the cooler temperatures.

Came home today and FINALLY the first bud was opened into a flower. These seeds were put in the ground mid-May! More blooms on the vine. They may germinate quickly, but take forever to form buds and half of forever to unfurl into a flower!!! But it smells heavenly and is about 7 inches across, truly magnificent.

It is October 5th and I had three moonflowers bloom last night. I am so excited. We had a real cold wet spring and only two plants survived. I thought the frost would get them before they bloomed. But we are in the midst of a warm spell now and my moonflowers say it's time to bloom. I hope the weather stays warm enough to see more. Cold weather is coming next week so not many of the buds will have a chance to bloom I am afraid.