Does Trimming Grapevines Produce Bigger Grapes?

Excessive Foliage

• Grapevines grow rapidly. A newly planted grapevine can easily add 30 feet of vine and hundreds of leaves in its first season. Grapevines grow to outperform other plants and gain as much access to the sun as possible, which in nature typically means growing up the side of a tree and breaking through the canopy. When you plant a grapevine in your garden, this same growth pattern continues. Your vine will add vine and leaves for photosynthesis, to the detriment of its fruit production. What few clusters you do get may appear small and shriveled, with a hardened skin.

Excessive Fruit Production

• A grapevine that is allowed to grow too woody and unwieldy will produce more grapes than it can ripen in a season. A second year vine can easily have 300 grape bunches if it is allowed to grow without pruning. This may seem like a windfall for you, but you will be lucky if you get 10 percent of that fruit to ripen. Your un-pruned vine will devote resources to all of its bunches equally, and likely wind up not being able to ripen most, if not all of them. Unripened or partially ripened grapes are smaller than their ripe counterparts and will have a sour taste when eaten.

Reduced Access to Sunlight

• There are competing schools of thought as to whether or not grape bunches need direct access to sunlight to ripen. Whether it is true or not, an unpruned, untrimmed, unwieldy vine will grow foliage on top of clusters and on top of other parts of your vine. This will limit the amount of sunlight reaching the fruit, and also reduce the airflow around the vine, opening up your crop to fungus and disease. Unripened, disease ridden grapes will tend to be substantially smaller.

Water

• A ripened grape is mostly water. Along with added sugars, the difference between a ripe grape and an unripened grape is the amount of water content in the fruit. An unpruned vine needs substantially more water for foliage growth and wood production, and therefore has less water to devote to its fruit. Pruning or trimming your grape vine will help your vine better allocate the proper amount of water for a bountiful, and sweet-tasting, fall harvest.