Answer: Mandevillas are tropical flowering vines that won't make it through our winters outside. They can be overwintered indoors. Here's how: Before frost kills it, cut it back to about a foot. You might also want to hose off the plant well or spray it with insecticidal soap so you don't take any bugs inside. Place the plant near a sunny window and water it just enough to keep it alive. Keep a dish under the pot to catch water that drains out the bottom. No need to fertilize.
The plant will get very leggy over the winter, but that's OK. The point is to keep the roots alive. Come next May, start fertilizing and giving it more water. Move the plant outside in a shady area. Gradually give it more sun and more outdoor time each day over a period of 10 days or so. Even then, the leaves may bleach out in the outside light, but don't worry. New leaves should replace them. Snip off any dead tips.
Once all danger of frost is gone and it's acclimated to sun all day, you can plant the mandevilla back in the ground and begin fertilizing monthly. By summer, you should be back in blooming business.
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