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Q. Who is Mr. Smarty Plants?

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Thursday - May 26, 2011

From: Point Pleasant, NJ
Region: Northeast
Topic: Non-Natives
Title: Promoting growth on non-native dipladinias (mandevillia) from Point Pleasant NJ
Answered by: Barbara Medford

QUESTION:

My Dipladinias were almost dead when I bought them last year, but after a little TLC, they blossomed like CRAZY in pots outside. They stopped blooming in November (I brought them into the house in September) and did well throughout the winter, with very little leaf droppage. Now they're outside again..but I bring them in when it's cold at night . I have 3 buds on a single stem for new flowers, but that's all..What should I do to promote new growth? I haven't fertilized (don't know what to use) and I haven't cut back anything (There are a million new shoots). I mist them regularly which they seem to like and don't let the soil get too wet or too dry. Also should I repot them? Thank you for your help!

ANSWER:

Mandevilla sanderi, formerly known as Dipladenia splendens, is native to the hills above Rio de Janeiro, Brazil but no longer found in its native habitat. The Lady Bird Johnson Wildflower Center is dedicated to the growth, propagation and protection of plants native not only to North America but to the areas in which those plants grow natively, so Mandevilla is out of our realm of expertise. This plant can be grown outdoors in USDA Hardiness Zones 10 and 11. In colder climates, it should be grown under glass or indoors.

Point Pleasant, in Ocean County, NJ appears to be in USDA Hardiness Zone 6a, which means your plant should definitely be considered a house plant. Whether it is hurting the plants to be taken abruptly in and out of your garden and returned to the indoors we can't say, but that may be part of the problem. Accordidng to the information we found, the misting is definitely a good idea. Your other questions are totally out of our field of experience, so we will try to find somewhere that you can get some answers.

From the Royal Horticultural Society (yes, England, they aren't native there, either) here is cultural information on Mandevilla. From Guide to Houseplants House Plant Care Tips has answers to some of your questions.

 

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