I live on Illinois and bought three Dipladenia plants at Menards. When I first got them they were very pretty and full. Now, leaves and becoming yellow and falling off and the flowers have white-ish spots on them. There are also far fewer flowers. What am I doing wrong? I know these are tropical plants, but it is the summer and they get plenty of sunlight. Am I overwatering? Is it insects? I'd really like help, as I think these plants are so pretty. I've attached a picture below. Thanks!

Welcome Beth. Hope we can help.

Have you checked the backs of the leaves for insects? Might want to use a magnifying glass for spider mites. Soapy water is the solution for those,1/2 tsp. Per quart of water.
Spray a couple of times per week for a while, and be sure to hit under sides of the leaves.

Could you post a pic of the whole plant or plants? They are fairly vigorous and might need repotting. Also just turning the plant out of the pot can give you a good indication of over watering.

Hi Beth,

from me too!

The white coloration on the blooms in your photo looks like water spots which can be alleviated by watering from the bottom. Yellowing leaves can be from overwatering and I'm wondering if the soil they are planted in perhaps is holding too much moisture. Some nurseries plant in very heavy soil that does not drain well, I assume to keep the plants moist while sitting on shelves in the garden centers waiting for consumers to buy them. Mandevilla/Dipladenia need a well draining potting medium. I also wonder if they could be root-bound, possibly in need of larger containers. I find Mandevilla also does best with some shade; bright indirect light but no direct sunlight, which will burn the foliage. For more blooms, fertilizer with higher phosphorus (high middle number) will help produce more blooms but only use half strength to what is listed on the package.

Good luck with your plants and I hope they do well for you. Even though they are tropical plants you can overwinter them by moving them indoors when temperatures dip below @ 50ºF. There are several Mandevilla (Dipladenia) listed in our database with information and photos: http://garden.org/plants/searc...

Couple more thoughts. Have you had cool nights, under 55deg or so?

Also how have you been fertilizing?