The Thompson grapevine is a seedless variety that produces long clusters with small-sized fruit that is ready for harvest in early fall. This variety is found growing in the hot, dry climates of the western United States, as it is sensitive to cold temperatures. Thompson seedless grapes are a popular variety used in raisin production and eating fresh. Thompson grapevines require heavy pruning and fruit thinning maintenance for best results with fruit production.
Select a planting area for the Thompson grapevine that receives full sunlight and has well-draining soil. Place the rows so they run in a north/south direction as this provides optimal sun exposure for the vine.
Test the soil pH prior to planting to verify it is at a basic level of 7.0 to 8.0. Work limestone into the soil to raise the pH or ground rock sulfur to lower the pH. Apply 1 inch of water to the soil and let it rest for two weeks.
Plant each Thompson grapevine at a distance of 5 feet apart in each row.
Water the Thompson grapevines after planting to moisten the soil to a depth of 6 to 8 inches. Apply 1 to 2 inches of water to the soil of young grapevines when the weekly rainfall is not adequate. Provide seven gallons of supplemental water each day to mature grapevines during fruit production.
Fertilize Thompson grapevines by working 1 to 2 inches of compost into the soil each spring. Chemical fertilizer applications are not required.
Promote large grape size by removing two to three grape clusters from each vine once they form.
Prune Thompson grapevines by cutting 75 person of the past season vine growth. Excess vines become woody and reduce production since fruit clusters form on 1-year-old vines.
Apply a fungicide at bud break if powdery mildew appeared on the grapevines the previous growing season.