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Grow & Care - Watermelon

Fast Facts

Light Requirements Full Sun
Temperature Adaptations Very Tender - plant about two weeks after the expected date of last frost.
Acidity (pH) Tolerance 6.8 to 5.0 pH
Salinity (Ec) Tolerance
How Pollinated Insects
Growth Habits Annual

Additional Information

Fertilizer Requirements

Use a high phosphorus fertilizer to promote fruiting. Large vines produce sugars to sweeten the fruits. Weak, neglected vines produce spindly, poor quality fruits. Fertilize with a ratio of one part nitrogen to four parts phosphorus at planting. Make your own by mixing fertilizers together or purchase a high phosphorus product.

Add nitrogen 30 and 60 days after planting to keep the vines growing. Large vines result from lots of water and fertilizer, so allow plenty of room. Minimum spacing essential for all but bush-type melons is two by four feet, but most need even more room. Close planting results in little or no fruit production.

Water Utilization

Provide adequate water. Watermelons have earned the name. If they are stressed, they stop growing and do not set fruit. Overwatering fruiting plants causes them to collapse from lack of oxygen. Check the soil moisture regularly and reapply as necessary before the melons start to wilt or go into stress. Allow the top 1" to 2" of soil to dry between watering.

Plant Development and Care

Watermelons need full sun and heat. Clear plastic mulches raise soil temperature by as much as 10 degrees. This helps melons come into production two to three weeks earlier than normal. Besides producing earlier melons, individual melons are larger and sweeter.

Melons are not good competitors and do not flourish if weeds shade them or compete with them for moisture and fertilizer. Remove small weeds to avoid stunting or stressing the melons. Avoid disturbing the root by cultivation as this weakens vines and keeps them from producing fruit.

Remember that seedless varieties require a pollinating (non-seedless) variety close by to produce fruit.

Melons are usually not bothered by many pests, but verticillium and fusarium wilt often develop if areas are gardened for many years. Rotate planting locations and use resistant varieties if plants die in midsummer.

Germination Time (Days)

12 days at 68 F
5 days at 77 F
4 days at 86 F
3 days at 95 F

Seed Germination and Temperature Range

77 F to 86 F

Common Fertilizer Deficiencies




The tone of the watermelon indicates ripeness. Lift the melon carefully and slap with a cupped hand. If the tone is high-pitched, the watermelon is not yet ripe. If it is low-pitched, it is too ripe. A medium-pitched tone indicates a ripe watermelon. Prac

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