Mandevillas going brown
I have 2 mandevilla plants in pots. For 3 years they have been doing well. Recently, I went away for 10 days and upon returning the plants are dying. Leaves are all brown and brittle. The heat has never bothered them before. Plenty of rain when I was away. Can this be caused by too much heat? They have been in this location for 2 years.
Did anybody water them while you were away? It sounds as if the plants have dried out and are in dire need of water. Plants in containers require more watering than those in the ground--once a day and twice daily in temps over 85 F.
If the stems are brown and brittle, then they are dead and it would be best to cut them back to wherever you see green wood. You should also soak the containers in water for about 5-10 min. to rehydrate the plants. Hopefully, they will bounce back.