Vine
Thompson Seedless Grape
Vitis vinifera 'Thompson Seedless' (syn. 'Sultanina') · Vitaceae
Also called: Sultana, Sultanina, Lady de Coverly
Thompson Seedless Grape (Vitis vinifera 'Thompson Seedless' (syn. 'Sultanina')) is a moderate-water vine well suited to Tucson and the low desert. It thrives in full sun, with a fast growth rate.
Thompson Seedless Grape at a glance
- Water use
- Moderate (established)
- Sun
- Full sun (6+ hrs); in the low desert benefits from some filtered afternoon shade and a trunk wrap or shade on the west side to prevent sunburn of bark and fruit.
- Mature size
- Vigorous vine, 15-30+ ft of cane growth per season; trained to 5-7 ft on a trellis, arbor, or 2-wire system.
- Growth rate
- Fast
- Bloom
- Inconspicuous greenish flowers; fruit is pale green to amber-yellow., Blooms spring (Mar-Apr); harvest mid-to-late summer (roughly July-August in Tucson).
- Cold hardiness
- Cold-hardy to about 5-10°F; fully hardy in Tucson (USDA 9a-9b). Deciduous, drops leaves in winter. Heat-tolerant but fruit can sunburn above ~105°F without canopy cover.
- Soil
- Well-drained soil; tolerates Tucson's alkaline, caliche soils if drainage is adequate. Amend planting hole and break through caliche layers. pH 6.5-8.0 acceptable.
- Native range
- European/Eurasian wine-grape species (V. vinifera); 'Thompson Seedless' is an old Persian/Mediterranean seedless cultivar popularized in California.
- Best used as
- Edible table grapes (fresh eating), Raisins, Shade arbor/ramada cover, Edible landscape
- Wildlife
- Birds and javelina/wildlife will eat fruit; netting may be needed. Flowers attract some pollinators though largely self-fruitful.
- Toxicity
- Fruit is edible for humans. Grapes and raisins are TOXIC to dogs (can cause kidney failure) — keep fallen fruit cleaned up around pets.
How to grow Thompson Seedless Grape in Tucson & the low desert
Watering
Deep, infrequent drip irrigation: roughly weekly in the hot growing season (every 5-10 days), tapering in fall and minimal in winter dormancy. Water to ~3 ft deep, then let the top soil dry between cycles. Avoid keeping roots constantly wet.
Fertilizer & nutrients
Light feeder; apply nitrogen (e.g., ammonium sulfate or balanced fertilizer) in late winter/early spring as buds swell, and again after fruit set. Zinc is commonly deficient in desert soils — apply a foliar zinc spray at budbreak. Avoid over-fertilizing, which forces excess foliage over fruit.
Pruning & care
Prune hard during winter dormancy (Dec-Feb). 'Thompson Seedless' fruits best on canes from spring growth and benefits from CANE pruning (leave 4-6 canes of ~10-15 buds each) rather than heavy spur pruning. Thin clusters for size.
Notes
Low-chill seedless grape (~100-300 chill hrs) well suited to Tucson; a classic ramada/arbor vine providing summer shade and dropping leaves to let in winter sun. Powdery mildew and grape leafhopper are the main pests; ensure airflow. Sunburn protection on fruit clusters and trunk is the key low-desert management point.
Sources: University of Arizona Cooperative Extension (Backyard Gardener / fruit & nut for Arizona); AMWUA Plants for the Arizona Desert; UC ANR / California grape culture references