PlantLife Online

Answer

The issues you are having with your mandevilla could have a number of causes. I would first determine if the plant is over or under watered, to check stick you finger about 2 inches into the soil it should be moist but not wet. A build up of salts may also be causing the foliage to turn brown, water directly from the tap in many areas may overtime cause a build up salts which will block the plant from absorbing water and nutrients. Solution, water the plant heavily with filtered water a couple times in a row this should leach out much of the minerals that have built up over the year. To much direct sun light could also cause a mandevilla to turn yellow and then brown, try moving the plant to different location with filtered light. This may take some process of elimination, I hope these tips will help. To overwinter your mandevilla trim the branches back to between 6-12 inches and store in a cool dark place, temperatures are best between 40-55 degrees, the plant should be kept from drying out completely water once or twice while it is dormant. Mandevilla can also be overwintered as a house plant, treat for pest before bringing indoors and reduce the fertilizer over the winter. Good luck.