I have a lovely full blossom Rio Dipladenia in outdoor container. It is too big to bring indoors to overwinter.
Could I take the bulbs out of the soil and store the bulbs over the winter. If not, can you suggest how I might keep the plant over the winter?
I absolutely love dipladenia and the similar mandevilla plants, and I certainly understand why you would want to over winter yours. These plants do not have bulbs but thicker roots known as tubers. The tubers absorb and hold water making it a very resilient plant during our hot summers as they can withstand not being watered for periods of time.
You mention you do not have room for it and I wonder if it is the pot size or the actual plant size that is the issue? If you have your dipladenia planted as part of a larger arrangement with other plants, I would suggest removing it, washing off the roots and replanting it in smaller clean pot with new sterile potting soil. This will ensure that you are not bringing in any insects or other critters hoping to overwinter in the pot. If it is the size of the actual plant that is preventing you from moving it indoors, I would suggest giving it a good pruning first. From my experience, I have had success with pruning them up to about half their size if needed.
Once indoors, place your dipladenia in as sunny a window as possible- south or south-west facing ideally. Water the plant when the top two inches of soil begin to dry. Allow the plant to “rest” until about late February when you can begin to fertilize monthly to encourage new growth and bloom in anticipation for its return outdoors in late May.
According the New York Botanical Gardens, the second option for over-wintering your plant is to allow it go dormant. They suggest keeping the vine outside until it gets cool and then moving it into a cool garage or basement that maintains a winter temperature above freezing, about 10C or 50F . If trying this method, you should cut the plant back hard to about 12 inches. Occasionally give it water so that it doesn’t dry out, but essentially leave it alone. Bring it inside when spring is just around the corner and let it start to grow. Then set it outside and enjoy this beautiful plant throughout the summer.
Hope this helps and good luck with your beautiful plant.