How to Make a Mandevilla Thrive Indoors

One morning this last fall, my friend Angela called to say she had some orphaned plants she wanted me to have because they needed a good home. You may remember Angela’s a dear friend who’s a container designer and regularly switches out arrangements for clients. In this particular instance, she’d redesigned some summer pots for fall and had a bunch of leftover babies.

Before I could blink, she was pulling into my driveway with a miscellaneous collection of pots and paper bags. The goodies contained bromeliads, crotons, a spider plant, and mandevillas. While I had some experience growing the first three, I’d never grown a mandevilla, outdoors or indoors. But I was game to give it a try.

What’s a Mandevilla?

For those interested, a mandevilla is a huge genus of vines that grow in tropical places like South and Central America. Some even grow in the southern United States. They can grow up to 15 feet, even higher given the right conditions. And those conditions are strong sunlight and warmth, which of course we don’t have much of during a rainy Seattle winter. But they can function as a houseplant.

The three mandevillas Angela gifted me all had the same strong darkish pink flower. Its trumpet-shape has inspired the common name, rocktrumpet. Unfortunately, I’m not sure of the cultivar. It’s somewhere in the black hole of Angela’s notes. But luckily I’ve been able to keep them alive well enough.

How to Grow a Mandevilla Indoors

Here’s what I’ve been doing that works.

First, I set it up in the sunniest window of my house, a south-facing living room window. It was okay there but after a few days, I put a grow light over it and it became much perkier. Its little vining shoots extended. It appreciated the bright light and extra warmth.

Second, I noticed some older leaves yellowed and dropped a couple weeks after I brought it inside. I discovered this was from the sudden warmth of dry heating vents that had started blowing in October. I cleaned up those dried yellow leaves and cut off whatever stems had dried out as well to deter pests. You can spot dried stems by their suppleness and color. Happy stems are always soft and greenish. Dried ones are blackish green or brown.

Third, I increased humidity near the plants. In one case, I misted the plant regularly. I actually don’t think misting is very effective but I didn’t have an extra diffuser so I sprayed the plant from a misting water bottle every few days. And sprayed liberally. You need to pretty much make sure the plant is soaked if you want the plant to absorb moisture before the droplets evaporate.

Fourth, I tapered off watering. I was watering lightly every week and now in the heart of winter, I’m watering about once every ten days. This has seemed to make the plant quite happy. And so far pests have not visited it even though mandevillas can attract pests if overwatered.

Fifth, in December, with less watering comes less light. I now turn on the grow light once every week rather than once every couple of days. It knows it’s winter and to be dormant. It’s not blooming and won’t for a while.

Springtime Growth

Heading into spring, I’ll let the season’s light do its work and turn off the grow light until next October. I’ll water every week again as the light strengthens. I’ll install trellises so its vines can latch onto a structure. And every month, I’ll add some fertilizer to see if it will bloom again.

We’ll see how things go. I might even put the plants outside in a hot sunny location. They thrived in Angela’s client’s garden so I might have the same luck. If those gorgeous flowers do bloom, the hummingbirds will surely visit and that will give me the best gift of all.