Isolation distance between ground cherries??

I'm growing Aunt Molly's Ground Cherries and Cossack Pineapple Ground Cherries this year.
Does anyone know what the isolation distance needs to be to keep the seeds pure?? I've looked on the web but only found a "guess" distance.
Thanks for your help!!

Seed to Seed says:
"All of the species of Physalis are inbreeding plants and have flowers that are perfect and self-pollinating. Tomatillo, P. ixocarpa, will not cross with any other Physalis species. There is widespread confusion about the classification of other Physalis species, however, so isolation or caging is recommended for seed purity."

Wow, is that really an answer. Lol I thought I was confused before.

I have the Seed To Seed book, and read that part, "...so isolation or caging is recommended...", but I haven't found a definite isolation distance. How far apart do they need to be???

....Me too, 1lisac! LOL

It may be that no one knows. Lacking formal field trials and testing -- which is not going to happen for a plant that isn't commercially valuable -- a "guess" may be all you are going to find. You could always cage them instead?

Good point NicoleC.....I bet you're right. The only "guestimate" I've found is 50 feet. I can get them as far as 90 feet apart with a block of corn growing in the middle. We'll start there and see what happens. :-) Thanks for all your help!!

I've also read that they and tomatillos should be started inside but I have found that once you grow either one you don't ever have to start them again, they keep coming back from seed...lol

I'm not trying to be unhelpful, but I'm guessing...a little further apart than your local pollinators fly. Which will of course vary tremendously by location, insect species, weather, etc. And that also assumes there are no wild Physalis within range that are capable of cross-pollinating with either of yours. Given that there are some 46 species of Physalis endemic to North America, that may be expecting a bit much. Please remember that just because a species is capable of self-pollinating is no assurance that cross-pollination cannot also occur.

In other words, the answer is ultimately unknowable except by experience growing in your own locale. Better I think to try isolating a few buds and maintaining isolation until the fruits start to form. I've wanted to try using the little cotton drawstring bags I've seen sold by some kitchen stores for immersing herbs in clear broths or brewing bulk tea. You might have to jiggle the blooms a bit you get them to self-pollinate - someone I know and trust told me it improved greenhouse tomato production, and given the similarity of the flowers it just might help. (I think they used a vibrator, but then they were big greenhouses).