I have a dipladenia that I bought this summer and plan on overwintering indoors (zone 7). There are some very small bugs on the tips, yellow in color and I don't really want to bring them indoors. What should I do to get rid of them before I bring it inside?
Those yellow bugs are probably oleander aphids. Here is an article that will give you ideas on how to contend with them - Horticultural soap sprays or neem oil work well for aphid control.:
https://www.gardeningknowhow.com/plant-problems/pests/insects/homemade-aphid-control.htm
My large plant is losing leaves suddenly at a tremendous rate. Some if its "trunk" parts have a white kind of cotton on them and a lot of dirt sticks to the leaves.
It sounds like you have both a Sooty Mold issue as well as Mealybugs.
Here are links that will help you with both of these issues.
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/mealybugs-control.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
Can I trim the tendrils back? They attach to the blinds as soon as I turn around!
Yes, you can regularly pinch back your Dipladenia.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
We purchased 2 Dipladenia Rio plants last year that were a riot of color and very beautiful. They were in the frost-free conservatory (we live in Torbay, Devon so winters are mild with hardly any snow or frost) but they died with the branches hollow. When taking them out of their pots, there are a number of tubers, looking like long potatoes. Should these be pot up and, if so, do we separate them? Would love more of these plants.
The purpose of tubers on mandevilla roots is to hold water reserves, they can't be split off and used for reproduction. When it comes to propagation, Mandevilla vines can only be propagated from seeds or cuttings. However, you can extend the life of your existing plants by overwintering them in pots - this extension article gives you two different methods on how to do so:
https://web.extension.illinois.edu/cfiv/homeowners/000930.html
When overwintering mandevillas, however, you need to water them only occasionally to ensure they don't dry out. Since yours appeared to be dried out and dead, I don't think you will be able to resuscitate it.
For more information on the care of dipladenia, please visit the following link:
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
I kept my dipladenia plant in the house over the winter and then when it got warm I put it outside. It looks really good but I wonder if I should cut it back. It has quite a few long vines and I don't know if it flowers on new growth or if it will flower on the old part. Thank you for any help you can give me. Don't know if I spelled the name right but it is like the Mandevilla plant. Thanks again. Ellen
You certainly can pinch back or trim the plant to encourage more compact growth.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
I purchased the Rio last year and it flowered a lot. I brought it inside over the winter and kept it alive. In March it started growing long vines at the top of the branches. I cut them off. I put it outside this year in the sun, and it has nice glossy foliage, but does not get flowers. It did get one more long vine that I cut off again. I also have some salvias in the pot, in case they make a difference. Why does it not get flowers? Thanks.
This article will help refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
I live in Washington State so cold winters and summers are common. I think this flowering vine is beautiful and wish to plant in a pot that can be hung so I can easily move it indoors when weather isn't suitable for it (which means it would be a "houseplant" most of the time, and instead of letting it trellis up, I would let/clip it so it hangs down), as winters are dark (at times only 4 hours of oftentimes filtered light is common). I have installed 2 "under cabinet" T8 24 inch hanging lights for added much needed synthetic sunlight.
Forgot to mention, the T8 24 inch bulbs are plant/aquarium bulbs, I can get higher UVB bulbs, but would have to move the plant somewhere else, as I have some low light plants in the hallway area