All watermelons need more oxygen during germination than many other seeds. Transplant producers have found seedless watermelons to be even more sensitive to soil saturation than regular watermelon seeds. Watermelon is a warm-season plant of tropical origin. Seed germination and plant growth are best at warmer temperatures. Transplants should be 3 to 4 weeks old and have 2-3 true leaves when planted in the field.
Older transplants suffer significant transplant shock.
Breeders are trying to develop seedless cultivars with better germination and seedling vigor, but until then, transplants are the best approach. Triploid transplants are very sensitive to cold injury and other stresses. Consequently, neither early germination nor seedling development are as vigorous as standard diploid seedlings. Once established, however, triploid watermelon seedlings show vigorous vegetative growth. A little extra care goes a long way toward insuring success in early yield and quality.