Production Practices

Seed germinates best at soil temperatures of 68–95°F, and planted 1 inch deep. 1–2 pounds seed required per acre, depending on seed size, germination and plant spacing. Icebox watermelon can be spaced more closely together in the field than picnic types, and in-row spacing is 2–3 feet while between-row spacing is 5–6 feet.

For transplants production, allow 3–4 square inches per seedling. Seedlings should be between 3–5 weeks old with 3–4 leaves at transplanting. Seedless varieties may germinate very poorly, depending on variety and direct seeding is not recommended.

Watermelons bear separate male and female flowers on the same plant (monoecious). Only female flowers set fruit. Bees are necessary for pollen transfer pollen. For successful seedless watermelon production, bees are especially important as seedless varieties do not produce pollen. The pollenizer variety is planted in alternate or every third row, or as every third plant in the row. Use a distinctly different variety as pollenizer in order to easily distinguish seedless fruit. Icebox varieties used as pollenizers result in early yields; picnic varieties used as pollenizers result in greater total yields. Icebox varieties usually flower 7–10 days earlier than picnic varieties, so delay icebox pollenizer planting.

Seedless Watermelon

Seeds for producing seedless watermelon are made by crossing a female parent that has the normal two sets of chromosomes (2N, also called diploid) with a male parent that has twice the normal sets of chromosomes (4N, referred to as tetraploid). The tetraploid parent is formed by treatment with cholchicine, a plant-derived chemical. The female parent of this cross sets fruit, and the fruit will contain seed that is 3N, which is referred to as triploid. These triploid seeds will grow and produce seedless watermelon plants, but the triploid plants are sterile and can’t reproduce.

Triploid watermelon seeds that result from this process generally have poor germination compared with normal diploid seeds, and are slow to emerge and become established. Specific temperature and moisture conditions are required for triploid watermelon seed germination to be successful. It is generally recommended to grow triploid watermelon as transplants so they receive special care and attention during this critical growth stage, rather than seeding directly in the field.

While triploid watermelon vines will bear female flowers that will set fruit, the male flowers are sterile, that is, they do not produce viable pollen. Therefore it is necessary to plant a diploid watermelon variety next to the triploid plants in order to provide a source of pollen. Most garden seed packs of triploid watermelon will contain a smaller pack of diploid seeds to be used as the pollinator variety. The general rule for seedless watermelon production is to plant in the garden or field 1 diploid plant for every 2–3 triploid plants.

When the diploid plant pollinates the triploid plant, fruit will be formed. But because the female parent has an uneven number of chromosomes (3N), it is unable to sexually divide (sexual cell division is referred to as meiosis), and so no seeds can be formed.

2013 Cost Estimation of Producing Seedless Watermelon in Eastern Washington (PDF). WSU Extension Fact Sheet FS150E. 6 pages. Published October 2014. In addition to the publication there is a Microsoft Excel worksheet available. To download the worksheet, use the following link (Excel File).

Processing and Utilization

Most of the U.S. watermelon production is consumed fresh. Per capita watermelon consumption in 2003 was 13.7 pounds and watermelon is about 1/3 more popular in the Western states then in the Midwest and East. About 85% of watermelons are purchased at the retail level for home consumption. Other processed products include roasted seeds, pickled rind and watermelon juice.