Hydroponic gardens can grow almost any kind of plant in a soil-free environment. Many fruits and vegetables thrive in this environment, including leafy greens, tomatoes, peppers, carrots and watermelons. Due to their size watermelons require some special handling in certain hydroponic setups, but with some care and attention to keeping the levels of the nutrient solution adequate, watermelons can be a fun and easy hydroponic crop. They are best grown outdoors or in greenhouses with plenty of natural light.
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Watermelons will grow in virtually any kind of hydroponic system, provided it is large enough to support the big vines. A simple hydroponic bucket system, where the plants are grown in individual buckets, works well, but it can be somewhat labor-intensive because the nutrient solution level must be checked frequently in each bucket. An ebb and flow system is a better choice as multiple containers are fed from a single tank, so there is only one place to check liquid levels instead of many.
Watermelons will grow in most kinds of hydroponic nutrient solution. Many ready-to-use nutrient mixes are available, and which one to use is largely a matter of personal preference. A simple nutrient solution can also be made at home by mixing 1 gallon of water with 1 tsp. of Epsom salts and 2 tsp. of any good quality, water-soluble fertilizer. The nutrient solution should be drained and replaced every two to three weeks. If the reservoir levels get too low in between changes, the solution must be topped off with plain water to avoid the buildup of excess minerals in the system.
Since watermelon vines are so large, it is best to root them in an inert growth medium that gives the plant some support as it grows. Perlite works well as a growth medium, but growers may prefer something heavier, such as clay pellets, pea gravel or silica stones. Any of these will add weight to the container the watermelon vine is growing in, thus providing some extra stability.
Watermelons can be planted much closer together in a hydroponic garden than they can when planted in soil because they do not need to compete for their nutrients. When they are planted close together, training the vines to grow on a trellis minimizes the overall area needed to grow watermelons as well as keeps the fruit off of the ground. Vines are tied or clipped to a sturdy trellis as they grow, and extra care needs to be taken to make sure the developing fruit is fully supported so the vine doesn't break.