Dear Aggie

How are seedless watermelon produced if there are no seeds?

It all comes down to traditional cross-breeding. A seedless watermelon is basically a sterile hybrid. Think of a mule: cross a donkey with a horse and you get offspring (mules) that are sterile. Very simply, seedless watermelons are produced by crossbreeding two distinct types of watermelon plants to create a hybrid. A watermelon that has the standard two sets of chromosomes is crossed with a watermelon that has four sets of chromosomes. The progeny contains three chromosomes. This results in sterile seeds that do not develop. These appear as soft, white seed coats that are barely noticeable. The hard, mature seeds of a typical watermelon are rarely found in seedless varieties.

Interestingly, seedless melons were first developed about 50 years ago. They are not considered genetically modified organisms as no genetic engineering was involved in their creation. Even today, plants must still be hand pollinated. Due to the labor involved, the seeds for seedless watermelon are often very expensive -- $5 to $12 for a packet of a half-dozen to dozen seeds.

If you would like to grow your own seedless watermelon, Cornell University recommends that following varieties for gardens in New York State:

• Tri-X-Sunrise produces melons averaging from fifteen-to-eighteen-pounds.
• Solitaire is a variety of mini watermelon producing fruit that averages about 4 pounds.
• Farmers Wonderful produces eight-inch fruits that average about 15 pounds each.

As these seeds are expensive, our growing season is short, and our summers are cool, we recommend that you get a head-start by germinating watermelon seeds indoors under lights or in a greenhouse. Transplant them only after the weather and soil warms, usually around the first of June. Choose the hottest part of your garden as melons enjoy heat. Well-drained sandy soils are ideal. Planting melons through black plastic is another method used to both control weeds and warm the soil. Expect your first harvest about 85 days after transplanting into the garden. Even with these methods, know that it can be difficult to get melons to ripen completely before the weather cools here in the North Country.

One important thing to note is that seedless varieties require a seeded pollinator. You must interplant the seedless varieties with traditional seeded watermelons. Viable pollen from ‘regular’ watermelons is needed to stimulate fruit production in the seedless varieties. In commercial production, where hundreds or thousands of plants are planted into a field, seed companies often add seeded varieties to seed packets to ensure fruit set of the seedless variety. In a home garden, it is often better to select and plant a seeded variety yourself to ensure that you have at least one pollinator rather than relying upon the luck of the draw in a small seed packet.

Question answered by Sue Gwise, Consumer Horticulture Educator. Contact her at sjg42@cornell.edu.

Last updated June 23, 2022