The first step in growing juicy and delicious watermelons is to choose what type you want to grow. There are three main kinds: early season, main season, and seedless watermelons. Within those categories you can choose flesh that's red, pink, yellow, or orange.
An early-season watermelon is sometimes called an icebox melon because it grows to a petite size that easily fits on a refrigerator shelf. It takes the shortest amount of time to mature, about 70 to 75 days.
A main-season watermelon is larger and takes longer to ripen, usually 80 to 90 days.
A seedless watermelon represents an interesting exercise in plant genetics. Plant breeders make several crosses to create seeds for watermelon plants that can't produce seeds themselves but can grow fruit when their blossoms are pollinated from regular seeded watermelons growing nearby. Seedless watermelons grow like other types of watermelons. However, because they're not busy putting energy into producing seeds, seedless types are often sweeter and the vines become more vigorous throughout the summer.
In some northern climates, the growing season may not be warm long enough to produce good watermelons from seed. Two to three weeks before your last frost, start watermelon seeds indoors. Plant watermelon seeds in a soilless potting mix.
Keep seedlings warm and moist until outdoor temperatures consistently stay above 50 degrees F or warmer. Don't start watermelon seeds too early, as large plants transplant poorly into the garden; once planted, watermelons don't like their roots disturbed.
You can sow watermelons directly into the ground when the soil temperature is above 65 degrees F. Plant seeds 1/2 to 1 inch deep, placing two or three seeds in groups 18 to 24 inches apart. Once watermelon seedlings are established, remove two and leave the best watermelon plant in each group.
Watermelons need soil that is well-drained and sandy. They also need a pH level between 6.0 and 6.5—a very narrow range. Test your soil before adding any compost or fertilizer to know if you need to add any nutrients and in what amounts.
Avoid "weed and feed" types of fertilizers. They contain weed killers that kill fruit and vegetable plants. They also kill annual flower seeds but are fine for use around shrubs and perennial plants.
To suppress weeds and keep soil moist, apply a 1- to 2-inch layer of organic mulch around watermelon vines when they reach 6 to 8 inches long. Frequently hand-pull weeds when they are small; if you wait until weeds are large, the weeds' large root systems could disturb a watermelon's shallow roots.
Once watermelon vines begin producing blossoms, the key to fruit set is pollination by bees. Avoid spraying for flying insects; chemicals can kill the beneficial bugs your plants need.
Why are some melons so sweet while others seem to be fibrous and tasteless? To get high sugar content, you must keep watermelon plants happy all season with the right amount of water, protection from diseases and pests, and the addition of extra nutrients to the soil.
An especially cool growing season can also affect watermelon quality.
Seedless watermelons may not germinate as well as other watermelons, so start more seeds than you need indoors in peat pots. Once they're transplanted into the garden, follow the same directions as for seeded watermelons.
Seedless watermelons need pollen from a seeded type to produce, so you must plant both kinds near each other.
How do you know when a watermelon is ripe? It's complicated, but here are a couple telltale signs:
Don't rely on the time-honored "thump" method. It simply doesn't work.
Experts suggest washing whole watermelons with clean water before slicing to remove potential bacteria.