July is National Watermelon Month

No matter how you slice it, there is no summer without watermelon.   Royal Sweet or Icebox, seeded or seedless, I’m not finicky about watermelon.  According to USDA estimates, each American consumes about 15 lbs. of watermelon a year.  By July, I’m way ahead of that mark.  Because  July is National Watermelon month, according to joint resolutions passed by the U. S. Senate and U. S. House of Representatives in 2008 and 2009, respectively, I feel that must support the consumption of this delectable fruit.


Leading watermelon-producing counties in SC. Credit: SC Watermelon Board and SC Watermelon Assoc.

Watermelons can be cultivated in any home garden in South Carolina, however,  major commercial production* is concentrated in counties in the Sandhills and Lowcountry, notably Aiken, Allendale, Bamberg, Barnwell, Colleton, and Hampton counties. Chesterfield county leads production in the Piedmont. Most of the watermelons are seedless, which comprise about 70 percent of the melons produced in South Carolina.

I do like the convenience of seedless watermelons, but I miss the crunchiness of the seeds and the opportunity to show my kids that their dad may be old, but he can still spit a watermelon seed farther than them.

Have you ever wondered where the seeds of seedless watermelons come from?  Seedless watermelons were first developed at Kyoto University, Japan in 1939.  The parents are two seeded varieties. The male is a diploid variety, that is a watermelon with the ordinary number of 22 chromosomes.  The female parent, however, is a tetraploid variety, one that has been treated with colchicine to double the chromosome number to 44.  The resulting hybrid seed is a triploid with a chromosome number of 33.  Although these triploid seeds will sprout, the resulting watermelon plant is sterile. The vine flowers and makes fruit, but these fruit are seedless.

Sakata Seed America

‘Citation’ watermelon. Credit: Sakata and National Garden Bureau.

Breeders select diploid and tetraploid parent lines separately for desirable traits, such as taste, flesh color, size and shape, rind thickness, productivity, maturity time, and others. Once the parent lines breed true, that is the offspring exhibit consistent traits, which may take ten generations–the crosses are made. As a group seedless watermelons tend to keep longer in storage since there are no seeds to serve as focal points for the decay.

Growing seedless watermelons is somewhat more challenging than raising ordinary watermelons.  Seed of the latter will germinate at 75 degrees. Seedless watermelon seeds, by contrast, need at least 80 degrees and preferably 85 degrees to sprout.  The thick seed coat sometimes sticks to the cotyledons on the emerged seedlings requiring them to be carefully removed by hand, though sowing the seed so that the pointed end is down  reduces this seed coat-sticking problem.

Seedless watermelon flowers must be pollinated to set fruit, but because the plants produce no pollen of their own, a seeded watermelon variety must be grown nearby.  When you buy seedless watermelon seed, a few seeds of another variety are typically included.  Plan on growing one of these seeded plants for every three seedless ones. These seeded watermelons will set fruit of their own, but these are usually selected to have a different shape or rind color to make it easy to distinguish the seeded and non-seeded fruits.

To learn more about watermelons, check out the National Garden Bureau’s 2013: Year of the Watermelon.

*Commercial watermelon producers should come to the Edisto Watermlon day on July 10.


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