I’ve always loved seedless watermelons, but if they don’t produce seeds, how in the world do you grow them? SJ

That’s a very good question, especially since gardeners spend so much time cultivating and planting seeds for their home gardens. The story about seedless watermelons is pretty interesting, so here we go.

Seedless watermelons have been around a while, but they are still a relative newcomer being introduced about 50 years ago. Early versions of the seedless watermelons we know today were not as sweet and flavorful, but fortunately for us, plant breeders have improved them over the years to taste more like we expect a watermelon to taste.

Technically, seedless watermelons don’t have the mature black watermelon seeds we are used to. There may be a few, but not near the number in the standard seeded varieties. Instead you will find immature, white seed coats that are perfectly safe to eat.

These seedless wonders come into existences through a little creative cross-breading. This is not a GMO process, just creative cross-breeding to achieve a result.

Chromosomes are the building blocks of life. The expected number of chromosomes in a watermelon is 22 which is called a diploid, with the “di” in diploid meaning “two” as in dissect - to cut in two. When you have watermelons with 22 chromosomes, cell division is pretty standard, and they produce egg cells and pollen with 11 chromosomes that combine to produce the standard 22 chromosome watermelon.

By using a chemical process, the number of chromosomes can be doubled from the standard 22 to 44 which is called a tetraploid (tetra meaning four). Then when the pollen of a plant with 22 chromosomes comes in contact with a female flower from a plant with 44 chromosomes, the resulting seed will have 33 chromosomes known as a triploid (tri for three). This plant with an odd number of chromosomes tends not to produces viable eggs or pollen in the resulting plant.

Since these triploid plants will not produce pollen that is viable, a standard diploid watermelon needs to be planted nearby to produce pollen that is used to fertilize the triploid plant. The bees and other pollinators typically do the work for you but these plants can be hand pollinated if you so desire. Either way, the triploid plants will need viable pollen to bring about fruit set and the fruit will be “seedless.”

Seed companies utilize the appropriate watermelon plants to produce the seedless watermelon seeds. When you order seedless watermelon seeds, they also send you some standard diploid watermelon seeds since you will need them for pollination. This is why seedless watermelon seeds tend to be more expensive than standard watermelon seeds. While this may seem above the pay grade for the standard home gardener, you’ll never know until you try. Good luck!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.

Photo: Oklahoma State University Agricultural Communications Services