Yellowing and Black Spots on Mandevilla - Knowledgebase Question

Avatar for ldichiaro
Question by ldichiaro
January 21, 1999
I have a Mandevilla plant I am wintering over in the kitchen. The leaves are dropping and turning yellow with black dots. Can you tell me what the problem is? I have checked the back of the leaves and don't see any mites or insects.

Answer from NGA
January 21, 1999
Mandevilla winters best in a large pot in a location with full sun such as a conservatory might offer, so it is probably not all that happy in your kitchen. In my experience it is best to keep it as cool and bright as possible with reduced watering and no fertilizing for the winter. (It will eventually lose some leaves and look quite awful in protest, but don't worry.) Promptly remove and destroy any badly spotted leaves. In spring, cut it back, repot and resume watering and fertilizing and set it outside again where it can enjoy lots of sunshine and good air circulation. It should recover to grow and bloom beautifully again.

Avatar for LynnnieBNC
A comment from LynnnieBNC
February 16, 2019
I keep mine under LEDs in the basement with palms and hibiscus. It looks great!

Name: Nancy
North Dakota (Zone 4a)
A comment from comgoddess
February 16, 2019
I have considered doing that as well with my hibiscus. What lights do you use if I may ask?

Name: Chuck Pfeiffer
McKinney, TX (DFW) (Zone 8a)
Avatar for chuck7701
Answer from chuck7701
February 16, 2019
Definitely cut way back on the watering as suggested, be it mandevilla, hibiscus or bougainvilla. I place mine in the garage to overwinter, keep the pots on the dry side to avoid root rot, and force or let them go dormant, losing all their leaves. Early January, trim or shape them for new spring bud growth. I move them out for periods between freezes, sun light exposure and a good drenching. After frost danger, pull em out of pots, knocking the old dirt off the ball and roots. Then repot with fresh soil and lots of composted fall leaf mulch. Usually mix in some organic fert with new soil, but otherwise don't fertilize until after it warms up and active new spring growth emerges.

My experience is they come back stronger and better after the dormancy, as if they've been recharged than keeping alive and green in the winter. Hibiscus especially like to be root bound, and flower growth is delayed if the pot is up-sized. I usually reuse the same pot, only up-sizing the pot when top growth exceeds pot capacity.

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