We just purchased two mandevilla vines. In researching how to tend to them, I read that they need a trellis to grow on (of course), but that to keep them alive in the winter they should be taken indoors. Obviously, the whole trellis could not go indoors. Should they be cut off the trellis at some point? If so, when and how much?
They are usually grown indoors unless you live in a warm climate. If you are leaving it outside for summer and bringing the plant idoors for over wintering, you can cut the plant back by a third. This article should help you with its care: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
I have a mandevilla. I transplanted it a couple weeks ago and now the leaves are turning yellow but still has new growth. Do I need to worry? If so, what should I use on it? Thanks for your help.
It is likely suffering from shock, which is a normal response in new plantings as they adjust. This article will help with that: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm
Now the leaves have black spots, are turning yellow and falling off. Any ideas? I have it in a huge clay pot on front porch. ccasey@harkeylambeth.com
It sounds like your plant has a fungus. Treat the plant with fungicide. I like to use neem oil as it is safe for people and pets and also will address any pest issues the plant may have. Here is more information on it: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
I have your "Tips for Proper Mandevilla Care" but don't know what brand fertilizer to buy.
While there are numerous to choose from, you might try Miracle-Gro Water Soluble Bloom Booster Flower Food (15-30-15) or Shultz Bloom Plus Water Soluble Plant Food (10-54-10), though really any type will work as long as the phosphorus ratio is higher. You may also want to consider adding bone meal to the soil to increase phosphorus. Here is more information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/bone-meal-fertilizer.htm
What causes white mold on mandevilla vine and what to do for it?
This is powdery mildew. This article will help:
https://www.gardeningknowhow.com/plant-problems/disease/get-the-cure-for-powdery-mildew.htm
I purchased a full size mandevilla this summer from a garage sale. It bloomed beautifully all summer long, just gorgeous, most favorite plant I have ever owned!. However, I am sick, the leaves on my plant (which is still on our patio in the same spot it has been in all summer) are now turning yellow and falling off. We have not moved, or changed any care for this plant. Please help, I surely do not want this plant to die. Thank you.
There are many reasons this can happen. Yellow leaves are a sign of a stress of some kind. This article will explain more:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm
I would check the pot. Make sure the water gets all the way into the soil in the container and that it is still draining properly.
My mandevilla plant leaves are rapidly turning yellow and falling off.
There are a number of reasons why the leaves may turn yellow. One might be overwatering. Too much water causes yellowing of the leaves and mandevilla do not like overly wet feet. Another possibility could be too little water. If this is the case, the yellow leaves would be curling up as well. 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). Mealy bugs can occasionally affect these plants, causing them to become weak and leading to yellow foliage. Finally, plant stress due to a change in location, temp., etc. can lead to yellow leaves.
Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm