Re: when to harvest Concord grapes?
Usually when they are around 16% or better for sugar content. I would imagine in your area around late September depending on the season. I've harvested as early as Sept 21 or as late as October 15. You don't want to harvest too early or the grapes will be quite sour. Probably your best bet is just taste. If you have a killing frost you should pick them, but its better to pick them before. Concord is considered
a late ripening grape but ripening times will vary from year to year and the season.