upper leaves are turning yellow and curling
This article will help you.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
In the past week or so my mandevilla leaves have started to turn yellow, some with some small brown blotches, and the leaves are falling off. This is widespread, not just at the bottom. The plant is otherwise doing extremely well, growing well, with lots of flowers. It is in part shade and I checked the roots for sogginess and they are fine (not soggy, not dry). I use a dilute fertilizer every few weeks that is - - .
Since there are brown spots in addition to yellowing leaves you may have some fungal leaf spot going on. Here is info on how to treat it, plus other environmental and disease causing problems.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-disease-problems.htm
Plant has full Sun, potting soil plus African violet soil, great drainage, periodic MiracleGro water-mixed fertilizer, and a metal and plastic trellis. Recent weather dry, then rain. No bugs seen on plant or in soil.
These are very sensitive to full sun. This needs to be in a shaded area, or dappled sunlight. This is the reason that it is dying. This article will help: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
I have a white mandevilla plant and was wondering why the buds and flowers are turning brown. Have always had mandevillas on my deck and have never had this problem before. Thanks
This is a common issue with potassium and phosphorus deficiencies. Are there any other symptoms, or just this? If there are other symptoms, then it may be a fungal/bacterial issue in the soil. If the leaves appear healthy, then a dose of fertilizer made for mandevillas will correct this.
This article will help to learn when and how to feed these: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/fertilizing-mandevilla-plants.htm
I have 2 plants in one pot. One of them is dying. I don’t see any bugs. The soil is moist but not wet. Thoughts?
it sounds like they are doing what they would in the wild- Competing for root space. The one that is stronger will usually take over if there is not quite enough space for both of them.
This article will offer information on their care in container: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
I have two Mandevilla plants (red blossoms) and am having trouble this year with the plants. During the summer months here in Central Texas the weather is hot (ours are placed in partial sun only). There were no flowers this past season. For the last three months the plants have been producing new leaves quickly...but they turn yellow and drop right away. No flowers and the plants look sick...but the new growth is doing well...except that leaves drop so fast. Not sure what I am doing wrong...in previous years the flowers were beautiful. The plants are about 6 years old.
I've included some articles below that might help uncover the cause of the leaf drop, from environmental to fertility to disease and pests. If none of these answer your question, contact your local extension agent for more information.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/fertilizing-mandevilla-plants.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-disease-problems.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-pest-problems.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
The light is poor in winter in my house. I have no windows with direct sun. I would like to use artificial light and keep the plant growing as it was a special mothers day gift from my daughter. Is it possible in winter?(Michigan).
Yes, that's possible.
Learn more about grow lights here:
https://www.gardeningknowhow.com/houseplants/hpgen/what-are-grow-lights.htm
Do a Google search for " grow lights Michigan" and you will see a list of suppliers.