Does your "blackberry jam" plant actually taste like blackberry jam? I've got one, and I have to say that the fruit tastes absolutely terrible! I"m wondering if I just have a bad plant or if the "blackberry jam" fruit really doesn't taste good. The blooms are beautiful and have a wonderful fragrance, though - so I'm keeping it.
I have not tried one yet, but from what I have read, it sounds like it is variable between plants, and conditions - like most fruit. There might be a cultivar to be had in there somewhere. I have 2 of them, so I really hope at least one of them produces something good!
Would be really interesting to see too what kind of variables in soil and climate and water might influence flavor. Sometimes too, like with many fruits, it might simply be a matter of the plant maturing more, or an early or later season fruit picked. Is it really clear when to eat them, so that we are sure the reports of poor taste don't have to do with fruit not being fully ripened? There doesn't seem to be a ton known about the fruit, or at least widely available, so I am hoping maybe sometimes it's a matter of people trying them too early or something? (Wishful thinking, but still...)
I just know how variable these things can be. Sometimes a plant just produces poor-tasting fruit, but I don't think so many people that I've heard rave about their experience of it could all be wrong. It seems very likely that either their plants are better, or their conditions are better. It's like a discussion that was had with Australian Beach cherry, how many people said it was useless and then some have identified at least one strain that is clearly highly desirable in flavor. Same with Natal Plum, they vary widely. The one I tasted was good, but some apparently are pretty awful.
One of my Blackberry Jam Fruit bushes had its first flower this past year, so I'm really hoping to finally get fruit the next time around! Then we'll see if they are in fact awful or decent or delicious. The flower was pretty cool though, so it's true, there is value in the plant anyway, at the very least as an ornamental.