The growth period of sweet 4k watermelon is generally **70-90 days * *. At seedling stage, the plant height of watermelon will increase with time. In about 50 days, the watermelon plant will reach the maximum height, at this time, the watermelon plant can grow to 2-2.5 meters, and the watermelon itself will change from green to yellow-green, and the fruit will become bigger and bigger. Most watermelon plants will grow within 70-90 days. At this time, watermelon plants can grow to 3-4 meters, and watermelon fruits will become very full and can be harvested.