You can keep your mandevilla plant in the winter alive by choosing one of two approaches. The first is growing it as an active houseplant near a bright window. The second is letting it go dormant in a cool dark space. Both methods work well and your choice depends on how much light and room you have inside your home.
Before you start overwintering mandevilla, give the whole plant a thorough pest check. Look under every leaf for whiteflies, spider mites, and mealybugs. These pests love to hitch a ride indoors and can spread to your other houseplants fast. Spray the vine down with a strong stream of water from your garden hose. If you spot any bugs, treat the plant with insecticidal soap and wait a week before bringing it inside.
Your mandevilla enters a natural rest period as daylight hours shrink. The plant slows its growth and may shed some or most of its leaves. This is a normal response, not a sign that something went wrong with your care. The vine is saving its energy for the spring growth push that comes later. You don't need to fight this process. Let it rest and it will come back strong when warm weather returns.
I keep my mandevilla in a cool basement each winter with just a small grow light running 8 hours a day. The first time I tried this method I was worried the plant wouldn't make it. The vine drops most of its leaves by January, and the stems look bare. I water it once every two to three weeks and skip fertilizer the whole time. By early March, fresh green buds start pushing out from the nodes. Each spring it comes back bigger than the year before. The third-year plant gave me more blooms than I could count.
Good mandevilla winter care means keeping temps above 50°F (10°C) at all times. Cut your watering back to once every two to three weeks per Clemson Extension. Stop all fertilizer until spring arrives and new growth appears. The soil should dry out between waterings during this rest period. You want the mix to feel dry an inch or two down before you add any water. A moisture meter takes the guessing out of this if you aren't sure about your soil's dampness level.
If you choose the active houseplant route, place your vine near a south-facing window that gets at least four hours of direct sun each day. The plant will keep some leaves and may even put out a flower or two during mild spells. You'll water more often with this method since the plant stays somewhat active. Check the soil every week and water when the top inch feels dry to the touch.
A friend of mine lost her mandevilla the first winter because she kept watering it on its summer schedule. The roots sat in wet soil for weeks and rotted before she noticed the problem. I've seen the same mistake happen to several other gardeners in my area. Cutting back on water is the single most important change you make for winter. Your plant needs far less moisture when it's not growing and pushing out new blooms. Give it just enough water to keep the roots from drying out and nothing more.
You'll know it's time to wake your plant up when you see new growth appear in early spring. Start watering more often and resume feeding with a 10-20-10 fertilizer every two weeks. Move the vine outdoors after your last frost date passes and give it a week of shade before putting it in full sun. Your mandevilla will reward you with a fresh round of blooms within a few weeks of making the transition.
Read the full article: Mandevilla Plant Care and Growing Guide
