I am also in zone 6 and some of mine are ready. I can tell because the seed pods are dry and splitting, brown and ready to dump out onto the ground. I take a bowl out to the garden with me and cut off the seedpod, catching the ripe seeds as I go. If you harvest them while they are still green, the seeds will be a light color, instead of the dark, almost black little pellets.

If you haven't grown canna from seed before, it's important to know that you have to "nick" the seeds before planting. I just use an emory board to file off a bit of the color down to the white part and plant it. Just file one little spot, not the whole seed. I had 100% success last year with my seeds growing. Good luck!

If you harvest the seeds before they are mature (dried), they most likely will not be viable. I currently have some forming on Intrigue and two seedlings I grew this year.

Intrigue has some very large seedpods and the one from the Dawn Pink seedling is a monster LOL. I want to grow the seeds from it for sure to see what I get since the seedling is a lovely dark rose pink with copper foliage.

Seedling from Tropical Sunrise has a lot of seeds, too, but not as large so not sure if they are actually making viable seeds or not.

Happy Gardening to all!
Peggy

Thanks folks.