I'm curious as to whether anyone might know of a species that has a shrub growth. I know there are some out there, and I'd love to get my hands on one if I could.
I've never grown any, but I think you want to look at Passifloras that are in the subgenus Astrophea.
I think your best bet for actually growing one would be buy Passiflora pittieri from Grassy Knoll Exotics. I checked, and it says they have a waiting list. You should contact Elizabeth Peters to find out how long it would take to get it. I would not necessarily assume that the wait will be long. I remember a friend told me a couple years ago the wait for P. antioquiensis was only 3 weeks; I think in other cases it can be longer.
You might also ask whether they have other Passifloras with a shrub-like growth. They might have some in quantities too small to post on the site. Or young seedlings. Who knows. I do remember that a couple years ago they were selling Passiflora lindeniana.
I remember Liz Fichtl (Arghya Gardens) was growing, and I believe selling, Passiflora pittieri a few years ago. I don't know if this is still the case.
The only other possible source that comes to mind is Butterly World. They sold Passiflora macrophylla and Passiflora tica seeds. This was a couple years ago, and I don't know if they currently sell any Astrophea. A friend bought both of those, I think, and got germination quickly with P. macrophylla (less than 10 days, if I remember correctly).
I just did a search and ran across a company selling 5 seeds of P. tica for $30.00.
P. pittieri for $15.00 at Grassy Knoll is a better price than anything I'm aware of and would probably be the easiest way to grow one of the shrub or tree Passifloras. If I remember correctly this plant likes it on the warm side, such as one might find in S. Florida, whereas P. lindeniana likes cooler temperatures, such as those found in coastal California. However, you should check into it to be sure.
I think the chance of anyone offering you seeds, cuttings or plants of any of these for trade would be small. However I would love to be proven wrong.
Here is a link that might be useful: Passiflora pittieri at Grassy Knoll Exotics
Thanks, I'll give it a look. I appreciate all the information. I know it's a shot in the dark to try to find one of a small fraction of them that would do well in 6B, but I'm up for the challenge.
Yeah, you can tell how popular P. pittieri is by the waiting list! :)
The varieties Randy mentioned would probably do fine during the summer months but none of those (and very few others) can remain outside over the winter in zone 6.
Yeah, we do have some native varieties of the vine version of the plant that grow around here. I know that the chances of having a shrub that can tolerate the winters is possibly not good, but I may just try a container to start.
I think the chance that any Astrophea can survive zone 6 is zero.
Just about the only passies that can survive a zone 6 winter are lutea and maybe caerulea and incarnata. Don't waste your money on others if you plan on leaving them out over the winter. They can be easily wintered over indoors. You can cut the vines back to a manageable size and keep them under artificial light. Just watch out for sucking insects like mites and mealies and cut way back on watering while inside.