Question:
The grapes on our concord grape vine will not get ripe, they stay green and hard until they dry up and fall off. Is there something we can do to prevent this?
Hardiness Zone: 7a
JC from Greensboro, NC
Answer: JC,
A common problem that plagues concord grapes is uneven ripening. This is when some (or most) of the berries within a grape cluster ripen unevenly. Some of the berries remain sour, hard and green, while others continue to develop normally. The grapes that fail to ripen may grow to a full size, but they don't soften and they never see the increase in sugars and decrease in acid that occurs during the normal ripening process.
Uneven ripening can affect a small or large portion of the total grape crop and seems to happen to grape crops every few years. This problem is only associated with concord grapes and although the reasons are not completely understood, it's thought to be due to hot temperatures, overcropping (allowing the vine to produce more fruit than it is capable of bringing to maturity) or canopy shade. Concord grapes do not tolerate high temperatures, which is why commercial productions of this variety of grape is not common in your area.
Still, many people have success growing them in the backyard garden. Have you had some unusually warm weather this summer? For more information on diagnosing grape diseases, check out this bulletin from North Carolina State University: http://www.ces.ncsu.edu/depts/pp/notes/Fruit/fdin012/fdin012.htm
Ellen
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