I have a yellow mandevilla. It looks very healthy, but the blossoms start to open, and then they fall off. I don't see any pests.
It could be that it is just a little underwatered, just enough so that it can't support its flowers and so it drops them.
It could also be that you have thrips. These are tiny pests that attack the base of buds and cause them to fall off. They can be very hard to see.
I would recommend increasing water just a bit and also treat the plant for thrips. This article will help:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
I received a mandevilla plant while hospitalized last June. It blossomed for a long time and was very pretty. I've kept it through the winter. I also pruned it back some. How will I get it to bloom like it once did?
Once the weather gets warm, take it back outside. Give it a phosphorus rich fertilizer and it should bloom wonderfully.
Do pretty crimson mandevilla have to be planted outside, and if so, how do you plant them; or is it an indoor plant?
Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
I have kept it watered and fertilized with Miracle Gro.
It may have thrips. This article will help with that:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
It also would not hurt to increase watering. While you are watering, it may simply not be enough for the plant.
I have been watering the plant daily, as it has been very dry here. The buds have begun to fall off. The leaves are green and the plant looks healthy. Please help me. Thanks
My ruby red mandevilla vine in L. A. keeps getting yellow leaves all over. It has not flowered yet. It gets about 6-7 hrs of sun now. Is that too much? Why are the leaves turning yellow? Is it too much water?
Mandevilla favor humid conditions. If your plant is exposed to the sun, the soil may be too hot. Try misting/spraying the leaves with water in the mornings and keep the soil moist (NOT wet). You may also want to consider moving your plant (if possible) to an area that doesn't receive direct sunlight for extended periods of time.
Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
The leaves are very yellow, and most have small black spots on them. The plant was transplanted before the blooming season. I fertilized lightly, sprayed with a soap and water solution, but the problem is worse than ever. Plant is two years old.
It sounds like a fungus, likely black spot. Treat the plant with a fungicide and this should clear up the problem.