Every year, I bring in a New Guinea impatiens at the end of September. And every year, after about 2 weeks, the leaves fall off or dry up and only a stub remains. A few weeks back, you recommended in one of your articles that it’s best to bring tender plants in early, before they undergo any cold. Does that mean that part of the problem is that I start doing it too late? Or should I just abandon the idea?
Grand Falls, Minnesota
You live in an area well known for its cold autumn weather. I figure you must live in hardiness zone 3. That’s a zone where frost is not unknown even in August. So, logically, yes. You’d certainly be a prime candidate for “early entry”. Absolutely, you’d do much better to bring your plant in before it gets too cold.
Now, add to that the fact that this impatiens is known to be “difficult” to overwinter in general: it’s not just you who has problems with it. Few gardeners manage to keep it growing over the winter for very long. It’s generally easier to buy new cutting-grown specimens from a commercial greenhouse in the spring, when it’s sold with the other “annuals” that will decorate our gardens through the summer. And nurserymen certainly aren’t unhappy that their customers find the New Guinea impatiens difficult to keep. That ensures a great boost in sales in the spring!
But that said, this impatiens is still not a “true annual”, a plant that goes through its entire life cycle, from seed to bloom to seed, in one year. Instead, it’s a perennial, but a tropical one, though: hardiness zones 10 to 12.
New Guinea impatiens is native, as its name suggests, to New Guinea, but also to the Solomon Islands and other islands in Oceania. The original species, Impatiens hawkeri, is highly variable. So much so that it was originally grouped into 14 different species (I. schlechteri, I. mooreana, etc.) before taxonomists decided that it was just one very elastic species that fit quite nicely under just the name I. hawkeri. The large flowers come in varying shades of pink, purple, white, orange, and red, as well as various bicolors. All flowers have a long spur filled with nectar, a reward for pollinators… but often hidden from view at the back of the flower.
The toothed leaves are 3 times larger than those of its more popular cousin, the garden impatiens (I. wallerana), of African origin, the famous shade impatiens (the New Guinea impatiens is not quite as shade resistant). New Guinea impatiens leaves also come in different colors—green, purple, variegated with white, yellow, pink or red marks, etc.—even in its natural state. In cultivation, of course, hybridizers developed new varieties that are even more colorful and variable than the wild forms… and better garden plants, too.
The plant forms a rounded dome of thick, succulent stems, reaching up to 2 feet (60 cm) in height and diameter, although modern varieties are often more compact: 8–20 inches (20–50 cm) in height and 10–16 inches (25–40 cm) in diameter.
Unlike woody tropical plants (shrubs and climbers) such as pelargoniums, fuchsias, hibiscus and mandevillas, where you can sometimes force the plant into dormancy by cutting back on watering and keeping it cool during the winter, New Guinea impatiens is not drought tolerant. If you let it dry out, it simply dies! So, “forced dormancy” is not a method you can use in looking for a way to overwinter your plant.
Start Early When Bringing in a New Guinea impatiens
To overwinter a New Guinea impatiens, start very early in the fall, before the nights are cold. When they near 55°F (12°C), it’s time to get moving. That could be as early as the end of August in colder areas. If you keep houseplants outdoors for the summer, this would be the right time to bring them in as well.
Bring in either stem cuttings (root them under high humidity, such as under a dome or in a mini-greenhouse) or cut back plants you dig out of the garden back by two thirds. Water them well and bring them indoors into a warm spot.
Mind you, these are mountain plants: they don’t need hot temperatures. Fairly cool indoor temperatures, 5 to 10°F (10 to 20°C), would be perfect. As spring approaches, raise that a bit to simulate the coming of summer conditions.
Maintain high humidity (60% minimum) and fairly intense lighting. Ideally, you’d give them full sun in the morning and partial shade in the afternoon. Artificial lighting (using fluorescent lamps or LEDs) may well be necessary. Don’t expect much bloom in fall and winter, those aren’t their main flowering seasons. Instead, they’ll start to bloom more and more abundantly in spring and summer.
This is a tricky plant to water indoors. It rots if overwatered, but wilts very quickly—you’d almost swear it had melted!—if not watered enough. The secret is to wait until the soil is dry to the touch, then water thoroughly with lukewarm water.
A weakened plant attracts pests and a New Guinea impatiens is always stressed in our homes. Shower the foliage regularly to control spider mites and thrips.
As Spring Approaches
Around March, you can take cuttings under high humidity (place them under a dome or inside a clear plastic bag) to increase the number of plants in time for the upcoming gardening season.
Later in the spring, when outdoor temperatures warm up, you can start to acclimatize your New Guinea impatiens back to summer conditions for a 2nd flowering season. The plant should be in flower again before the end of April!