When you want to enjoy homegrown seedless watermelons, you are likely to need to find a use for a few seeded fruit also, since seedless triploid watermelons don’t create fruit unless seed-producing diploid melons grow nearby. Triploid watermelons, which have three sets of chromosomes, are crosses between ordinary watermelons, called diploids — meaning that they have two sets of 11 chromosomes –and tetraploid watermelons, which were chemically manipulated to have four sets of chromosomes. Triploids can’t produce seed, since their chromosomes can’t line up in pairs. Triploid seeds are catchy to germinate, so purchase them as transplants in the event that you can find them. Once growing, their needs are no different from diploid varieties.
Clear weeds and stones from a website in full sun in the warmest microclimate of the garden — one which receives reflected heat in a south-facing fence or wall, or is in a greater elevation; raised beds are ideal. Allow enough space for a single diploid to each two to three triploid watermelon plants with plants spaced two to three feet apart in rows, together with at least two feet between rows.
Work 5-10-10 fertilizer into the ground with a shovel as soon as it’s dry enough to work. Use the fertilizer at a rate of 3 pounds per 100 square feet.
Spread black plastic sheeting, at least 1.5 millimeters thick, above the watermelon bed or down the row where the watermelons are to be planted. Secure the borders of the mulch with wire garden staples, or soften the edges of the plastic in garden soil. This solarizes the soil, making it 10 to 20 degrees Fahrenheit warmer than surrounding soil for spring planting. Watermelons need both warm air and soil temperatures to grow nicely.
Cut “X”s with a utility knife in the appropriate spacing in Step 1. Peel back the black plastic mulch from the middle of each “X,” and tuck the points beneath the mulch to make a 5-inch-square hole at each cut.
Dig small holes with a trowel from the gaps from the plastic to fit the root balls of the watermelon seedlings. Alternative two to three triploids for every diploid plant on your rows.
Mark that the diploid plants with plant markers.
Give all the plants a good soaking.
Monitor the plants as they grow, watching for flowers to bloom. Female melon flowers occur singly on long stems, have a little bulge at the base of the blossom and are available for only one day. These are the fruit-bearing blossoms. Male blossoms, the pollinators, bloom in clusters on short stems.
Fill an open male blossom from a diploid plant from its stem, and carefully eliminate its petals in the morning to a day when a female flower on a triploid plant is freshly open.
Roll the middle of the male diploid blossom from the stigma at the middle of the female triploid blossom.
Water deeply once a week when leaves wilt from the midday sun. Decrease watering once fruit reaches its full dimensions and starts to ripen. Less water intensifies the taste of the fruit. Fruit is generally older 90 days after planting.