Thinning grapevines in the spring is a crucial practice for American grape growers aiming to enhance fruit quality, ensure vine health, and optimize yields. This process, known as shoot thinning, involves the selective removal of shoots to manage canopy density and promote better air circulation and sunlight penetration. Proper timing and technique are essential to maximize the benefits of shoot thinning.
OSU Extension Service+1Extension | UGA Cooperative Extension+1ONfruit
The Importance of Shoot Thinning
Shoot thinning serves several vital functions in grapevine management:
- Improved Airflow and Sunlight Exposure: Reducing shoot density enhances air circulation and sunlight penetration within the canopy, which helps in reducing disease pressure and promoting even ripening of grapes.
OSU Extension Service+1Extension | UGA Cooperative Extension+1 - Balanced Crop Load: By managing the number of shoots, growers can balance the vine’s vegetative growth with its fruit production, leading to better fruit quality and vine health.
- Facilitated Vineyard Operations: A well-managed canopy simplifies other vineyard tasks such as spraying, pruning, and harvesting.
Wine Grape Growing
Timing of Shoot Thinning
The timing of shoot thinning is critical to its effectiveness. It should be performed when shoots are approximately 5 to 12 inches long. Thinning at this stage allows for easy removal and minimizes potential damage to the vine. Additionally, waiting until after the last expected frost reduces the risk of losing primary shoots to frost damage.
OSU Extension Service+5ONfruit+5Wine Grape Growing+5ONfruit+3Ag & Natural Resources College+3Facts for Fancy Fruit+3Wine Grape Growing+1WSU Extension+1
How Much to Thin
The optimal shoot density varies depending on the grape variety:
Facts for Fancy Fruit
- Vinifera Varieties: Aim for 3 to 5 shoots per linear foot of canopy.
- Hybrid Varieties: Maintain 4 to 6 shoots per linear foot. Facts for Fancy Fruit+1Wine Grape Growing+1
- Native or Labrusca Varieties: Keep fewer than 15 shoots per linear foot. Extension | UGA Cooperative Extension
Over-thinning can lead to excessive sunlight exposure and potential sunburn of the fruit, while under-thinning can result in a dense canopy that fosters disease development.
OSU Extension Service
Recognizing the Right Time to Thin
You can determine it’s time to thin when shoots reach about 5 inches in length and the risk of frost has passed. At this stage, it’s easier to identify and remove non-fruitful or weak shoots, ensuring that the remaining shoots are well-spaced and positioned for optimal growth.
Wine Grape Growing+3Penn State Extension+3ONfruit+3
Risks of Over-Thinning
Thinning too much can expose grape clusters to excessive sunlight, leading to sunburn and negatively impacting fruit quality. It’s essential to strike a balance, retaining enough foliage to protect the fruit while ensuring adequate airflow and light penetration.
Continuous Thinning Throughout the Season
While the primary shoot thinning occurs in the spring, some additional thinning or canopy management may be necessary as the season progresses. However, excessive or late-season thinning can stimulate unwanted lateral shoot growth, increasing canopy density and negating the benefits of the initial thinning.
Proper Techniques for Shoot Thinning
When thinning shoots, consider the following techniques:
- Identify Non-Fruitful Shoots: Remove weak, non-fruitful shoots, especially those growing in crowded areas of the canopy. ONfruit
- Remove Secondary and Tertiary Shoots: If a primary healthy shoot has emerged, remove secondary and tertiary shoots to prevent overcrowding. OSU Extension Service+3ONfruit+3Penn State Extension+3
- Eliminate Shoots from the Trunk: Remove shoots arising from the trunk unless they are needed for renewal purposes. ONfruit+1Wine Grape Growing+1
- Use Appropriate Tools: For shoots less than 12 inches long, hand removal is typically sufficient. For longer shoots that have begun to lignify, use pruning shears to prevent damage to the vine. ONfruit+1Facts for Fancy Fruit+1
For a visual demonstration of shoot thinning techniques, you may find the following video helpful:
By adhering to these guidelines, you can effectively manage your grapevine canopy, leading to healthier vines and higher-quality fruit.
I actually jumped the gun a little and did my thinning on April 5th. I had a wonderful Saturday morning with nothing else to do and great weather for being outside. I read up some and watched some youtube videos and just went ahead with my thinning. We are expecting 38 degree weather in a couple of days, but we shouldn’t have another frost this year (although we haven’t his Easter yet…)
To see the difference in my vines check out April 3rd photos and then April 6th photos to see the difference.