Why Does Watermelon Rot on the Bottom?

Soil Conditions

• Watermelon plants grow in a wide array of fertile garden soils, but all must supply good drainage of water. The best soils comprise organic matter with sandy or sandy loam. Gritty soils also work well. Overly wet or slow-to-drain soils promote root rot and other fungal diseases. If a developing melon fruit rests atop a wet soil, the same fungal rot problems that can inflict the plant also threaten the skin and rind integrity of the melon.

Poor Growing Conditions

• Even if the garden soil is well-drained, other factors can contribute to the soft and rotting bottom of a developing watermelon fruit. Cool, cloudy weather as well as lots of rainfall and high humidity can lead to soft melon bottoms, even if the soil is fast-draining. While the vine's leaves bask in sunshine, the shade and shelter created under the leaves can elevate humidity and slow the drying of the soil surface and the melon's skin.

Solutions

• Watermelon vines grow well in soils that are at least 70 degrees Fahrenheit and free of weeds. The shallow roots need an evenly moist soil, not uneven fluctuations between dry and moist conditions. Gardeners may lay black plastic sheeting atop the soil before making holes to sow watermelon seeds. The sheeting warms the soil, conserves moisture and prevents weeds. The sheeting also dries quickly, reducing the chances any developing melons sit directly atop moist soil. Puncturing tiny holes into the plastic around the melon ensures no low depression forms that can collect rain water. Alternatively, any coarse mulch under a melon improves drainage while keeping the melon's rind off the soil. Straw, dry grass clippings or pine needles work well. Even a flat, large piece of scrap wood or old roof shingle placed under the melon diminishes chances of bottom rot.

Handling Melons

• Do not lift and turn developing watermelons on the vine. Rotating the melon to change the part of the melon in contact with the soil is not practical and it increases chances of damage to the vine. Turning a melon risks snapping or cracking the attachment stem that supplies the water and sugary carbohydrates into the melon from the leaves. It's far better to place a bed of mulch or a board under a small melon early in its developmental stages than to turn and lift a larger melon to prevent bottom rot.