How do we get grapes to ripen on the vines?
Question:
Three years ago we purchased a home with mature grape vines. The tag says these are red, seedless grapes. We NEVER get ripe grapes. We get plenty of grapes that remain green until frost. Two years ago we cut them all back quite a bit. We do NOT let foliage shade the bunches of grapes. How can we get ripe grapes from these vines?
Answer:
Katherine Garland, Horticulturist
Great question. A few things might be leading to the lack of fruit. Here are some factors to consider:
- Pruning. It’s great that you cut back the plants a few years ago, but it was probably not enough. Grapes require annual pruning to ensure a proper balance between fruiting wood and vine production. Unpruned plants will produce smaller fruit, fruit that won’t ripen in a timely manner and will have weak stem growth that won’t produce as well in later seasons. Some summer shoot thinning might also help; just removing some of the more vigorous new shoots in July to open up the planting and thin the fruit load can help speed up maturity as well.
- Cultivar selection. Many grape varieties will survive our winters, but that doesn’t necessarily mean they are well-suited for production in our area. Some will require a longer growing season to fully develop ripened fruits. If pruning doesn’t do the trick and fruit is a top priority (verus simply having foliage for your arbor), then you may want to consider replacing it with a more reliable variety such as the following suggestions from our small fruit expert “For a red seedless type, I would suggest Somerset Seedless or Reliance. These would still need to be planted in a protected spot to prevent exposure to extreme cold and windy conditions. Something like Beta or Bluebell would be even hardier, but these are blue grapes with seeds, so it depends on your preferences for fruit type.”
- Site selection. Grapes thrive in full sun and well drained soils. If the conditions are less suitable, then they will typically not produce as many fruit. Handley also suggests “Trellising the plants to get the most sunlight can help, but may also increase cold injury due to less protection during the winter.”
- Water availability. This is not likely the sole cause of lack of fruitfulness, but may be a factor. Well established plants will benefit from supplemental water during dry seasons.
More grape info can be found here: https://extension.umaine.edu/highmoor/home/research/growing-grapes-in-maine/.