I would try some of the Chinese species and hybrids from them. There is a man in the D.C.area that tests a lot of begonias for hardiness with some success. I think diadema and its hybrids such as Little Brother Montgomery have come through their winters with very good results. I think he has also had good results with U508 but won't swear to it.

The other thing to do is try some of your plants and see what happens. Make sure you only experiment with part of the plant if you don't want to lose it.

I'm not sure about southeastern Pennsylvania but there are some newly introduced begonias that are fairly hardy, and some older ones are turning out to be hardier than anybody realized. Among the hardier species are B. emeiensis, B. formosana, and B. pedatifida. 'Torsa', 'Little Brother Montgomery' and 'Connee Boswell' are older hybrids that have turned out to be fairly hardy.

Most of these will survive a mild winter in zone 7; a cold winter (and our last several have been quite mild!) is probably another story entirely. The key is to start with healthy, well-grown plants, get them in the ground early in the growing season, plant deeply, and mulch in the fall. As long as the rhizomes don't freeze, many will return. For sources, check out the listings in the Plant Delights Nursery catalog. I would also suggest getting in touch with the Delaware Valley Branch of the American Begonia Society to meet fellow begonia growers and obtain new plants.

Here is a link that might be useful: Delaware Valley branch

Also check out this great article--written from a west coast perspective, but still lots of good information.

Here is a link that might be useful: A Bounty of (Hardier) Begonias

johnnieb

Thanks for all the info. Begonia emeiensis looks spectacular from the pic in the article you pointed out, and I think I'd try it even as a houseplant.

You're right that we have had really warm winters , 2_in_a_row. My H. niger has actually bloomed before Christmas both years and this fall, I had 1 lone bloom 2 weeks ago.

George

I re-checked the article and you were probably looking at the second photo (mis) labeled as B. emeiensis, which is actually 'Connee Boswell'. B. emeiensis is the first one, with large and rather ungraceful leaves. This species has been hardy for me through 3 winters, but wants a lot of water and isn't the most attractive begonia! I've given up on 'Connee Boswell', a spectacular plant that seems to dislike heat. (Your summers probably aren't as hot as mine, so you may actually have better luck with this one than I've had.)

If you're on Facebook, check out a group called "MidAtlantic Tropics". I post quite a bit there, including photos & information about begonias.

Here is a link that might be useful: MidAtlantic Tropics (Facebook)