Sunday, February 21, 2016

Growing Grapes for Wine? It's Time to Prune! by Donna Duffy

John Crawford, photo by Donna Duffy

My neighbor, John Crawford, is a fourth generation vintner. I recently asked him to share some advice on pruning vines for maximum grape production. Here’s what I learned.

First, purchase your vines from a reputable source. Be sure that you purchase vines grown for Colorado climate and altitude – hybrids and not varietals. John admits to trying to disprove the varietals-can’t-grow-at-6,000 feet myth for years – and failed each time due to early bud times and late season Colorado frosts.

For first year vines, plant them within a few days of their delivery from the nursery and don’t do any pruning, just let them grow. This gives the vines a chance to build their root system and store carbohydrates, providing energy to grow strong trunks and canes.

Photo by Donna Duffy
Pruning starts in the second year. There will probably be several shoots growing from the main vine – when they are several inches long (April?), find the strongest two and remove the rest. Some grape growers only keep one strong shoot, but John keeps two as a safeguard. Remove the side spurs, then tie these main shoots to a pole for straight growth. When a shoot gets about four feet tall, cut the top off to encourage side growth. One of the most difficult parts of growing grapes is pruning off all that growth in the second year – but don’t be sentimental! You are building the base for a strong, healthy grapevine in future years.

In the third year, intentional pruning is critical to control growth, promote healthy vines and provide an abundance of fruit. Grapevines are best pruned during the cold months of February and early March before the first buds emerge. If you miss this window of opportunity, wait until the leaves are fully developed to do your pruning.

Take these steps to prune your vines when they are at least three years old:

  • Follow a growing vine tip (called a spur) back to the older wood from the previous year.
  • Then, come forward leaving between four and ten buds and prune off the rest. John leaves three buds on every strong spur.
  • If you have weak, brittle spurs, cut them off.
  • Step back and take a look, your spurs should be about three inches apart. In future years, you’ll choose the three strongest spurs and they will be the base of your grapevine for the life of the plant.

John Crawford, photo by Donna Duffy

Finally, a couple of pointers on fertilizing. If you are growing grapevines to harvest grapes, fertilizing is not really needed if your soil was amended with organic matter at the time of planting. However, if you are more interested in growing a leafy vine (as in a barrier), application of a high nitrogen fertilizer in April will result in lots of leafy growth.

The result of proper pruning: wine! Photo by Donna Duffy
Pruning grapevines is complex and multi-phased. An excellent resource is Modern Farmer's Winter How-To: Tips for Pruning Grapevines.