Cultivar

• Different species of grapes have different harvesting times. In general, American cultivars are more cold hardy than French cultivars, and American cultivars are usually picked later in the season. Depending on what kind of grape vine you are growing, ideal harvesting time may occur anytime between mid-July and early September.
  
  

Red Grapes Ripening Clues

• The best way to know if grapes are ready to be picked is simply to taste them. If they appear to be of a decent size, try a red grape from the bottom of a bunch. If this grape is sweet and pleasant to the taste buds, the rest of the bunch should be ready to pick. If it doesn't taste great, the fruits aren't ready for picking. Either way, trying them out is completely safe and harmless.
  
  

White Grapes Ripening Clues

• White grapes are a little bit more complex than red grapes. One ripe grape in a bunch is no guarantee that the rest of the bunch will be ready to use. Be sure to sample grapes from all around the bunch before picking.
  
  

Pests

• It is a good idea to pick grapes as soon as they are viable for picking. Many pests, most familiarly wasps and ants, love ripened grape fruits for both consumption and egg laying. As soon as the grapes look full and taste sweet, get them off the vine and on their way to a bottle.