FruitWatermelon
Cal Sweet Supreme Watermelon
Cal Sweet Supreme is a classic picnic watermelon that delivers everything summer demands: fruits weighing 30-35 pounds with deep red flesh, ready to harvest in 90 to 99 days. This open-pollinated heirloom thrives in zones 3-13 and handles intense heat with remarkable toughness, making it reliable even in challenging climates. Its most distinctive trait is its non-lobed leaves, which naturally shield the developing fruit from sunburn, a built-in protection that reduces the guesswork in watermelon growing. Plant it in full sun during mid to late spring for a mid-summer harvest that feeds a crowd.
Photo © True Leaf Market
Growing Conditions
USDA Zone
3-13
Sunlight
Full Sun
Water
High
Soil
Well-drained, Sandy Loam, Fertile
Growth Stats
18 in
Height
TypeVining
Spacing
36
Plant Profile
Sunlight
Full Sun
Water
High
Zones
3-13
Size
18in H x ?in W
Growth
—
Care
Moderate
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Highlights
The non-lobed foliage is genuinely unusual among watermelons and serves a practical purpose, keeping sunscald off your fruit without extra effort. At 30-35 pounds per melon, Cal Sweet Supreme delivers serious yield without requiring a sprawling garden, and its heat tolerance means it thrives when other varieties struggle through hot spells. The dark red flesh and medium-small brown seeds create the classic watermelon appearance that tastes as good as it looks.
Common Uses
Cal Sweet Supreme is a traditional picnic watermelon, meaning it's bred for whole-melon enjoyment: sliced fresh, served chilled on a hot day, or shared among family and friends. The seeded nature of the melon makes it excellent for seed-saving, allowing gardeners to preserve the variety year after year if they keep plants isolated from other watermelon varieties.
Growing Timeline
No timeline data available yet for this variety.
Care Instructions
Direct Sow
Direct sow seeds into warm soil after the last spring frost date, when soil temperature reaches at least 70°F. Plant seeds 1 inch deep and allow seedlings to thin naturally or thin to appropriate spacing once established.
Harvesting
Harvest Cal Sweet Supreme watermelons at 90 to 99 days after planting, when the melon has reached full size (30-35 pounds) and the skin shows a deep, rich green color with a creamy yellow spot where it rested on the ground. Cut melons from the vine rather than pulling them, using a sharp knife to cleanly separate the stem. A ripe watermelon should feel heavy for its size, and tapping it should produce a deep, hollow sound rather than a high-pitched tone.
Growing Calendar
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Companion Planting
Ecology & Traits
Edible
Scientific Classification
Citrullus lanatus
Family
Cucurbitaceae
Genus
Citrullus
Growth Habit
Vining
Native Status
L48 (I)PR (I)
History & Origin
“Cal Sweet Supreme is an open-pollinated, heirloom picnic watermelon, meaning it has been grown and saved by gardeners over many generations. These seeded varieties represent watermelon breeding from an era before commercial hybridization dominated the market, preserving the genetics and flavors that made watermelons a summer staple long before seedless varieties arrived.”