How to Prune Thompson Grape Vines

Thompson grapes are a favorite grape types for gardeners to grow for using in cooking or eating fresh. This seedless grape variety grows well in zones 6 to 10. Grape production generally starts in June and ends in November. Gardeners can purchase the grapes in white, green or red. Though low-maintenance, grapes need yearly pruning to remove diseased canes and other unhealthy areas. Pruning grapes will result in healthier grapes, which means bountiful produce for the kitchen table.

Things You'll Need

• Bypass shears
• Lopping shears
• Denatured alcohol

Instructions

1. Choose a time in the late winter or early spring to prune your grape vines. Avoid pruning grapes too late in the spring, because it will cause sap to exude from your Thompson grape vines.

2. Examine your Thompson grapes for signs of fungal diseases. Downy mildew, black rot, crown gall and powdery mildew are common fungal diseases to infect grape vines. Look for fungal spores, discoloration or disfigured areas of the plant. Dip your bypass shears or lopping shears in a mixture of 70 percent denatured alcohol and 30 percent water in between cuts to prevent spreading any fungal diseases.

3. Cut at a 45-degree downward angle 1/4 of an inch above a healthy outward-growing cane. Remove all diseased debris like canes and leaves from underneath the plant, because fungal spores can travel through the wind or rain and continually infect the Thompson gape vine.

4. Prune off 85 to 90 percent of the 1-year-old canes. Pick canes to prune that look unhealthy, have few buds or are growing out of their designated planting location. Canes that have have 10 to 15 buds should be retained.

5. Cut off any canes that make the Thompson grape vine unbalanced. Thin the grape vine, so that there is at least six inches of space in between canes.

Tips & Warnings

• Prune off all but one cane after the Thompson grape vine's first growing season. You should choose the healthiest-looking cane to be the dominant cane.

• Avoid using bypass shears on any canes with a diameter larger than a pencil, because you can cause wounds or tears in the wood.

References

• Produce Oasis: Thompson Grapes
• University of California: Pruning Grape Vines