It is not more hardy and in fact, 20F is pretty generous for cold tolerance and I'd not like to test it :-) Typically, selections of Mandevilla sanderi (Dipladenia splendens) are hardy only in semitropical areas of the country, zone 10 and above (45-50F are generally quoted as the best minimum temperatures with 65-70F being ideal). You can cut it back and grow it as a houseplant for the winter - you don't necessarily have to hide it away in the basement.

I had a pink one that I bought from Costco last year that I loved. I cut it back enough to go into my cold greenhouse -- I only put heat on when the temp drops below freezing, but it died. I agree with Gardengal, this is a tropical that needs more warmth. I overwinter a number of other tropicals in this greenhouse with success. Please continue this thread with what you do and the success you have over the winter.

You can keep it going indoors with a grow light, you don't need to chop it and put it in the dark. They are evergreen vines.

Mine is three years old in my greenhouse and covered with blooms. I leave it in there all the time.

Sunset WESTERN GARDEN BOOK (2007, Sunset Publishing, Menlo Park) lists 'Scarlet Pimpernel' as one of the cultivars of M. splendens (M. sanderi, Dipladenia splendens) that is "lower growing and shrubbier than the species (to 6-8 ft.)" and "superb in hanging baskets". About the species in general it says "you can keep it bushy by pinching climbing shoots". Sunset Climate Zones listed for it in the book are ones found in southern California and Hawaii only.

Bummer! I won't take a chance leaving it outside, and my greenhouse will get too cold, too. I'm going to cut it way back and put it into the basement where it will never get below about 55. The basement is heated only by the hot water tank and the furnace(no vents in the basement, tho). If I water it once in awhile and leave it in the dark most of the time it'll be okay, right? Then I'll bring it back out into the greenhouse when I start my seedlings and have the heat on out there. I really don't want to lose this baby, it was the envy of all who saw it!

gardenerkarin I think that is the best choice for it. As you know it grows very quickly when the weather warms up so perhaps it won't take too long to catch up again. Please let us know how you make out. I was sorry to lose mine and I think I will buy another next year.

It will be interesting to see what happens. I would not think that an evergreen would appreciate being put in the dark though a deciduous plant like a fuchsia, datura or bougainvillea doesn't mind.

Okay, so it's March now and I've brought my mandevilla out of the basement and into the greenhouse. I've got my seedlings started out there with soil cables and the temperature stays well above zero all the time. The mandevilla is just brown woody stems with about 100 shoots about 12" long growing out all along the woody stems. No leaves - it was in the dark basement so the shoots were seeking light. My question is what to do now? Should I snip off all the new shoots or leave them? I've given it a good drink of warm water with fish fertilizer added, to start it off, but that's it.

Have you looked at Mandevilla laxa? It is white, so not as colorful as the more tender varieties, but it is very fragrant. It can also be grown year round outside in most areas in the PNW. I have been growing one for a few years now, and I really like it.

Gardenkarin at least it's alive. I wouldn't do anything for the time being. I had my brug cuttings in a dark basement all winter and when I brought them out there were white shoots which in 3 days have turned green and look quite healthy and are now growing. I hope this happens to your mandevilla.

I have tried several methods to over winter my mandevilla and finally came to the conclusion that it was not only easier to replace each year but the results were far better as well (at least for me). Every year I have at least a half a dozen in various locations. A one gallon can usually be procured for single digit dollars and the bang you get far exceeds that cost. I have glass rails overlooking my pond and train one up each of three posts and along the top rail. By frost, there's probably in excess of 100 blooms between the three. For under $30, it is a long and beautiful display.

Here's a pic from early in the season last year.

Here is a link that might be useful: {{gwi:1094834}}

Mine is lush and green in my heated greenhouse but it does have aphids....

The first year I had 'Alice' I splurged and bought a 5 gallon and grew it up one post of my pondside pergola. It went up and over the wisteria and was quite remarkable. I tried cutting it back and leaving it in the basement where there may have been too much light. It would start to get new growth and them die back. By the time I started looking closer at it, I discovered it had white flies and even though I treated it, by then I think it was just too late.

I've been watching now for a couple of days and the ends of the shoots are withering, but they are green, and the little leaf buds are swelling. I'm going to leave it alone for a couple of weeks and then reconsider my options. "Boxofrox", your mandevillas on your deck are wonderful. Mine grew almost 5 feet wide, and about 10 feet tall, (more like a bush) but definitely didn't twine & vine like yours - probably a different type. I will keep posting my updates - I sure hope I can keep this growing. "Buyorsell888" how do you heat your greenhouse? I'd like to find an economical method. Right now I just have heating coils set in sand on a bench where my seedlings grow - that area is about 65 - 70 degrees, but the rest of the greenhouse can be about 50 most of the time.

I have an electric heater. Not sure how economical it is but my plants would die without it.

karin,

From what I remember, the magic minimum number for most of the non hardy mandevillas is 45 so you will probably be fine. Last year I used Terosa on them and it sure seemed to make a difference.

BTW, thanks for reminding me how much I like them :-) I'm going to throw a couple of the hardier white ones into the mix this year.

Here is a link that might be useful: {{gwi:1094836}}