Hydroponic gardens use a soil less medium and liquid nutrient solutions to grow fruits, vegetables and other plants. Though you might think that the size of watermelons would make them hard to grow hydroponically, they actually grow quite well in such systems. The biggest concern with growing watermelons hydroponically is making sure that they have sufficient light and support for their weight.
Most hydroponic systems are suitable for growing watermelons. If multiple plants are being grown, then an ebb-and-flow system is the best option, because it uses a single reservoir to provide nutrients to multiple hydroponic units, reducing the amount of time spent checking nutrient levels and adding more solution. For smaller growing setups, a floating hydroponic system allows one or more watermelon plants to stay suspended above a container of nutrient solution.
A sterile, inert growth medium is important when growing watermelon in hydroponic units. Clay-based growth media or pea gravel provide additional support to help hold roots in place. Lighter options that hold liquid better include peat moss, coconut coir and pine bark shavings. Mineral-based media such as perlite and vermiculite can be used as well, as can artificial growth media designed specifically for hydroponic use. Sand can be mixed in with clay or gravel growth media to improve water retention if necessary.
Watermelons typically grow well with general-purpose fertilizers. Most general-purpose nutrient solutions contain balanced amounts of major nutrients, secondary nutrients and micro nutrients, allowing hydroponically grown watermelons to grow and thrive. A homemade hydroponic solution consists of 1 teaspoon Epsom salts and 2 teaspoons general-purpose fertilizer mixed into 1 gallon of water. Any nutrient solution used when growing watermelon in a hydroponic garden should be drained and replaced every two to three weeks to ensure that it contains sufficient nutrient levels.
Watermelon vines require a trellis or other support structure to grow hydroponically. Depending on the available space, the support structures can be oriented horizontally or vertically alongside the hydroponic units. For vertical supports, nylon mesh netting attached to a horizontal tensile wire will support the melons and keep them from snapping off the vine. Smaller watermelon varieties are more suitable for vertical supports; this will maximize melon production and prevent the melons from growing too large to be properly supported.
Watermelons require a significant amount of light to grow and thrive. For proper growth and development, watermelons should receive eight to 10 hours of direct light per day. If the hydroponic system is located in a greenhouse, this light will come in the form of natural sunlight. Indoor hydroponic systems require dedicated grow lights to supply the necessary light exposure, as standard indoor lighting is insufficient. Periodically trim the leaves if necessary to prevent them from growing too large and blocking light to other leaves on the watermelon vine.
Growing and Harvesting
Watermelons should be started from seed to grow in a hydroponic system. Start seeds in rock wool or peat starters, watering as needed to keep the starter moist until the watermelon plant begins to grow. Once the plant begins forming visible roots, transfer it to the growth medium and provide it with nutrient solution. When flower development occurs, pollinate female flowers using the stamen of male flowers to encourage fruit production. Harvest the melons when the tendrils closest to the melon begin to dry out and turn brown or when the white spot on the rind that rests against your support structure turns yellow.