Which are the hardy passifloras?
I recenty read of an arboricol passiflora P. arboricola from Ecuador. They say it grows at heights of 3000-7000 feets. Could be grown in a 7-8 hardiness area as well?
I think it's unlikely. Since the plant is found so close to the equator you'd have to go pretty high for it to be able to stand temps around 10 F.
Probably the easiest way to compare it would be to look at other species in that part of the world and see what elevation they are found at and what temps they can take in cultivation.
The data that are out there tend to be expressed in meters. The elevation range you gave is about 900-2100 meters. A couple examples, one from close to the equator and one even farther out are P. antioquiensis and P. umbilicata. From what I gather P. antioquiensis probably dies somewhere around 25-30 (a typical zone 9b winter), and I've heard P. umbilicata can take a few extra degrees (zone 9a??).
One good source of elevation data is Tropicos, which reports on where the species have been found in nature:
P. antioquiensis is close to the equator (as is Ecuador) and seems to be generally reported at 2000-3000 m, generally higher elevation than the one you are interested in, and it doesn't come close to growing outside where you are:
P. umbilicata is quite a bit farther from the equator and is from even higher up (2500-3500 m, roughly) and as far as I am aware can't survive zone 7-8.
In general, one would expect that such a plant from higher up and farther than the equator could take more cold than the one you ask about. It's been exposed to much colder temperatures in the wild than would one near the equator and at lower elevation.
That said, there are of course exceptions and surprises. But if you checked 25 species from the elevation and the latitude you suggest, I would be surprised if any could handle 10 F.
But you never know...however the odds are against it. If you have one to spare or if it's cheap you can always try. If it's hard to find, expensive and hard to propagate it's probably not worth trying.
Some selections of P. caerulea (Clear Sky is one example) can supposedly take temps down to -15 C (~5 F) and have stems/leaves survive the winter in a temperate climate. I have Clear Sky outside, so I'll give mine a good test this winter. I typically see minimum temps of around -15 C to -16 C at least a couple of times each winter.
Thks for the message, it is quite discouraging... (indeed, the arboricola is said to come form 1000 -2300 m altitude)
I already have a P caerulea, blue sky, and it took -20*C with ease, last winter, and this spring grew like fury!
kiwinut, thanks for the info on 'Clear Sky'. I just got one about 5 months ago. I'm on the cusp of zone 9B/10, so I have no worries personally about cold temps. I am looking forward to hearing how you make out this winter with this one. I bet it will be fine.
The 2 that I have found that are hardiest are the lutea & incarnata. You still have to mulch heavily and choose your location wisely when in a 6 or lower, but these both grow in a zone 5