Citrullus lanatus 'Ultra Cool'
Plant Common Name
Ultra Cool Watermelon, Watermelon
A self-sterile F1 hybrid, 'Ultra Cool' produces medium-sized, rounded, seedless watermelons with dark-striped rinds and sweet, reddish-pink flesh. Plants grow from seed to harvest in 90 to 100 days. This triploid cultivar (three sets of chromosomes) requires a diploid companion (such as 'Sugar Baby') for pollination and fruit set.
Watermelon is a tender annual tropical vine that needs a long, very warm growing season to produce its famous fruits. Yellow, bee-pollinated flowers appear among the attractive, deeply lobed, gray-green leaves throughout the growing season. Some watermelons flowers are male and others female. Female blooms have a bulbous ovary at the base, which will eventually become the fruit, and the males only have pollen-laden anthers.
Watermelons do not become sweeter after being harvested, so they must be picked when ripe. It is tricky to know when to harvest—especially considering the fruits take a while to mature and patience can wane. The best means is to monitor the tendril closest to the developing fruit. Once the tendril starts to turn brown, the fruit is ready. Another method is to keep an eye on stem health. When the stem is green and firm, the melon is still ripening; a soft withering green stem is an indication of ripeness, and a dry or unattached stem can mean over-ripeness. Finally, check the underside of the melon and give it a light knock. If the underside of the melon has turned from white to pale yellow and a hollow sound emanates from the fruit, it is probably ripe. When harvesting, cut the melon from its stem. Tearing the stem can lead to vine rot.
Full sun and fertile, crumbly-textured sandy loams are perfect for watermelon culture. Watermelon plants appreciate sharp drainage, so it is best to sow seeds in low mounds of soil (called "hills"). After the threat of frost has passed, plant as many as three seeds per hill and keep the soil evenly moist but not wet (wet soil can induce seed rot). Alternatively, plant seed in small pots (using a well-drained potting mix) and set out seedlings after the last frost date. Provide ample room for the plants to sprawl across the ground. The sheer weight and size of the melons precludes training the vines on trellises.
AHS Heat Zone
12 - 4
H1, H2, 1a, 1b, 2a, 2b, 3a, 3b, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24
1'-2' / 0.3m - 0.6m
6'-8' / 1.8m - 2.4m
Africa, Southern Africa