I dug up my mandevilla and transplanted it in a pot for the winter. The plant looks healthy and is still blooming but the lower leaves are turning yellow and dropping off.
Why Do Mandevilla Leaves Turn Yellow?
When you dug up the plant, some of the roots were left behind. Almost impossible to get all the roots when you dig up a plant. A plant has a certain number of roots for each leaf, so your mandevilla is now getting rid of some old leaves, just as you got rid of some of its roots. You can minimize the loss of leaves by acclimating your plant before you bring it indoors. https://www.gardeningknowhow.com/houseplants/hpgen/acclimate-plants-indoors-winter.htm