I have a diplodenia in a 10 inch clay pot...this was planted last spring, over wintered indoors, and brought back out the first of spring in Oklahoma, I think is zone 7...... How will I know when it is time to put in a bigger pot? It is beginning to bloom now so I'm not sure if I should bother it..please help! Thank you,
If the roots are filling the entire bottom of the pot or even poking out from the pots drainage holes, it is time to repot.
Look for a pot slightly wider but not taller then the existing pot. Proper drainage is important.
Repotting is a good time to add a trellis if you don't have one.
Use a good quality potting mix.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
Do you have a suggestion what to plant with the dipladenia in a whiskey barrel for added color?
You could perhaps find a shade ground cover plant that may fill in the container.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
https://www.gardeningknowhow.com/special/shade/ground-covers-for-shade.htm
Can I cut a Diladenia plant in half and repot in two containers and will they survive?
I would wait until early spring to divide the root ball.
Yes, Dipladenia can be propagated by seeds, cuttings, or dividing the root-ball; however, most new plants are produced from softwood cuttings taken in early spring. Here is more information: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-propagation.htm For more information on cuttings, check this article: https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm
Can these plants be hanging pot plants
Yes, I would pick a sturdy pot.
You may have to do pruning or clipping is vines get too long.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm
Wintered through and now outside and won't bloom.
This article will help you pinpoint the issue.
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/getting-mandevilla-to-bloom.htm
How can I disinfect the plants and soil from bugs before taking them inside for the winter? Will they stop bluming at some point, will they need less sun or watering over the winter? When should I put them out again in the fall? Can I divide them and when? What should I use to disinfect?
A mixture of one part dawn dish soap, one part mouthwash to four parts water, makes a good spray to rid plants of pests before taking them indoors. This article should help
https://www.gardeningknowhow.com/houseplants/hpgen/acclimate-plants-indoors-winter.htm
Can dipladenia be cut back when you bring it inside in the fall? -zone 6 Mattoon
In frost free areas, Dipladenia will be evergreen. In cooler areas, the plant will go dormant. Prune in late winter just as new growth begins. Reduce the overall size as you like and remove dead, diseased, damaged and rubbing/crossing stems. If it experiences winter die-back, cut it back to live growth even if that means cutting to the ground. It will grow back and flower the same season.