Care for an ailing mandevilla plant

Question

I bought 3 mandevilla plants this spring from Lowes and one of them seems to be dying. I planted them along a fence so they get plenty of sun every day, at least 6 hours. I have fertilized and mulched them and water about 2 times a week. The other two plants are doing fine. This plant gets about an hour more shade in the afternoon than the two healthy plants, but still gets a full 6 hours.
Help, please!
Don

Answer 1

If these are new plantings, make sure you are adequately watering. Depending on temperatures and soil, twice a week may not be enough.
Daily water for the first 2 weeks is generally required.

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm