Watermelon fruit is composed of approximately 92% water, requiring the plant to pull a large volume of moisture from the soil to reach its full size and develop its juicy texture. Managing the water supply correctly at specific times determines whether a melon will be large but bland, or perfectly sized and intensely sweet. The goal is to provide consistent moisture during vegetative growth and fruit enlargement, and then intentionally create a slight drought stress just before harvest to maximize sugar concentration.
Watering Newly Planted Vines
Young watermelon plants require a steady supply of moisture to develop the deep, extensive root system needed to support the future fruit load. During the first four to six weeks, until flowering begins, the plants focus on vegetative growth. The standard recommendation is to provide about one to two inches of water per week, adjusting upward during intense heat.
This early watering should be deep, encouraging roots to stretch at least six inches down into the soil. The soil should never be allowed to dry out completely during this establishment phase. Using drip irrigation or soaker hoses is highly recommended, as watering at ground level avoids wetting the foliage. Keeping the leaves dry helps prevent common fungal diseases like powdery mildew.
Peak Water Requirements During Fruiting
The period from flowering through fruit set and enlargement represents the plant’s peak water demand. As developing melons begin to swell, the need for water can double or even triple, especially during hot summer weather. A sufficient water supply is necessary to maintain the high metabolic activity required for transporting sugars and nutrients to the fruit.
Watering frequency will increase during this stage, often requiring daily attention in hot climates to ensure the soil remains moist six to eight inches deep. Inconsistent watering during this time can be detrimental to harvest quality. A sudden drought followed by heavy watering can cause the fruit to split or crack open, while severe moisture stress can lead to blossom end rot. Maintaining a consistently damp, but not saturated, soil environment ensures uninterrupted fruit development and maximum size.
Reducing Water for Optimal Sweetness
As the watermelons approach their final size, the watering strategy must shift dramatically to concentrate the sugars within the fruit’s flesh. Since watermelons do not increase in sweetness after they are picked, this final step is performed entirely on the vine. The mechanism works by slightly stressing the plant, encouraging it to prioritize sugar production over watery fruit mass.
Begin reducing the water supply approximately seven to ten days before the anticipated harvest date. This reduction is a gradual process, eventually stopping irrigation almost entirely once the fruit is nearly full size. If heavy rain occurs during this final week, it can dilute the concentrated sugars, so harvest should be postponed for a few days. Successful withholding of water results in a more intense flavor profile and a higher brix level, the measurement used to determine sugar content.