Growing Concerns 538: Overwinter white mandevilla, diversity


Summertime favorite tropical plant can spend winter indoors as houseplant

Dear Janet,

Is it possible to overwinter a white mandevilla in an unheated garage? If so, should it be cut back or left intact under a hotcap? They are trained to pyramidal trellises and potted in natural terra cotta.


Dear K.F.,

Temperatures below 50 can damage mandevilla. Anything below 40 will probably kill it. It also needs lots of light to remain healthy, even during its winter growth stall. So overwinter it in a warm sunroom -- 70 or warmer by day, minimum 60 at night.

Water it whenever it dries. Test for dryness by hefting the pot to gauge its weight or pushing one finger into the soil to see if it's warm and dry an inch below the surface. It will probably need water far less often indoors in the lower light of a house in winter than it did outdoors in summer. The reason you should be careful about watering is the same reason you should use tepid water and avoid placing the pot on cold tiles or sills -- soggy or cold roots cause leaf drop and other problems in mandevilla.

Mist it daily or grow it near a humidifier to keep its glossy foliage healthy. Guard against mealybug, mites, scale and whitefly by bathing the foliage often. Don't expect any bloom during winter.

Cut the plant back late next March, leaving only the sturdiest vertical shoots and shortening all side branches to just a few inches.

If you treat it very well over winter it will resume blooming next June on the new wood that forms after your pruning.

A great way to learn how to overwinter special plants is to visit garden centers that stock such plants year-round.

Short report

Hooray for diversity in ash tree replacements.

S.P.  writes, "I just finished planting replacement trees for the 30 ashes we had to remove here at the retirement community where I work. I planted only 13, which was enough  because the grounds had been overplanted to start. I am excited about the trees because I was able to plant ginkgo, American yellowwood, goldenrain tree and, my favorite, an awesome dawn redwood. Thanks for your advice to diversify, it has produced good results and my residents love it."


Green thumbs up

to preserving a few ash leaves for posterity. Because of the apparently unstoppable emerald ash borer, the clear gold or butterscotch of green ash and smoky wine of white ash foliage in autumn may become only a memory, all within our lifetime. Pressed ash leaves may one day be as precious as passenger pigeon feathers. 


Green thumbs down

to landscape professionals who aren't. Your shoddy and ignorant work makes me ashamed for the whole industry and treats your unsuspecting and trusting customers as badly as the plants. Be a real pro! Take a class, read current articles in journals or at university websites and learn how to plant so trees will thrive, not simply survive a warranty period. 


Originally published 10/18/03