Watermelon germination will only successfully take place when the soil is fertile enough and the seeds are watered properly. The fruit needs a significant amount of water, since this is about 92 percent of the watermelon itself. It's best to supplement the soil with black mulch to keep the soil moist; mulch also keeps weeds from damaging the watermelon plant. Germination time for watermelons is between three and 12 days; the seeds require warm temperatures -- 70 to 95 degrees Fahrenheit -- to develop a healthy seedling. Watermelon seeds also need plenty of room to grow; seeds should be at least five feet away from each other. Each seed must be planted about an inch into the ground.
Watermelons with yellow flesh germinate at various times during the warm season; the hotter the weather, the quicker the seed sprouts a seedling. For instance, it may take only three days for a yellow watermelon seed to germinate when temperatures are around 90 or 95 degrees Fahrenheit. Yellow Baby cultivars are early-season crops, meaning they take between 70 and 75 days to harvest. The fruit's insides are a pronounced shade of yellow; the melon weighs up to 10 lbs. at maturity. Yellow Doll watermelons are sweet and especially juicy, have minimal seeds and are usually between 3 and 5 lbs. The Honey Heart takes a little longer to harvest -- up to 85 days -- and weighs between 8 and 10 lbs.
Watermelons with red flesh are the most common and have more than one harvesting period. When temperatures are in the high 70s Fahrenheit, the seeds take about five days for germination. Seeds planted in slightly warmer conditions, such as the middle to upper 80s Fahrenheit, will sprout a seedling in four days. The Sugar Baby is a particularly sweet variety of watermelon -- gardeners can harvest it early in the watermelon season, usually during spring. The melons are between 6 and 10 lbs. and grow best on a south-facing slope that gets full sun. Crimson Sweet watermelons have dark-red fruit, minimal seeds and a succulent sweetness that makes it ideal for summer snacking. These melons germinate midseason and take about 88 days to reach full maturity. Crimson Sweet melons are larger than Sugar Babies and can grow as large as 25 lbs.
Seedless watermelons, which are all hybrids, take the longest to mature for harvesting. The germination time is between one and two weeks, and ideal temperatures are between 75 and 85 degrees Fahrenheit. Watermelons without seeds must be planted with a pollinator variety of melon -- any seeded watermelon variety planted near the fruits without seeds is sufficient. They grow best in a sandy, loamy soil and vary in size and flesh color. For instance, the Cotton Candy cultivar of seedless watermelon is about 20 lbs. and has pinkish red flesh. Honey Heart melons are about have the size of Cotton Candy watermelons; they grow between 8 and 10 lbs. and have golden yellow flesh, unaccented by black seeds.