Growing watermelons means you can eat sun-warmed, sweet, juicy fruit straight off the vine—a prime gardening treat.
Guess what? It is not difficult to grow watermelons. With a little attention to space, soil, and temperatures, you can grow great watermelons in any garden—or even raised beds.
Read on to learn how to grow a watermelon.
How long does it take to grow a watermelon?
Watermelons are hot-weather plants, so they don’t tolerate cold temperatures. Plant watermelons after the last frost in spring, but early enough to give them time to ripen before the first frost in fall.
Most watermelon varieties need at least 80 to 100 days to grow after seedlings are planted outdoors to bear ripe melons. Small, round varieties of watermelon like Sugar Baby, which are between 8 and 10 pounds, ripen around the 80-day mark. Larger, longer varieties like Jubilee or Allsweet, which can grow up to 25 pounds, will take around 100 days.
In short, the time between the last spring frost and the first fall frost is your growing season, also known as the frost-free season. You can find the average last frost date for your area using NOAA maps or search your zip code in the The Peasant Almanac Database. Just remember that “average” is not an exact date.
To extend your planting season, start growing watermelon seeds indoors or buy seedlings 2-4 weeks before your last frost date. Watermelon seeds can also be sown in the ground if your growing season is long enough.
How to grow a watermelon
Prepare the soil with organic nutrients
Watermelons do best in sandy, loamy soil with a pH between 6 and 6.5 that drains well. You can check the pH of your soil with a soil test kit. If your garden soil tends to drain slowly, consider building a raised bed and filling it with a mixture of soil, sand for drainage, and well-rotted manure or compost.
Make sure the soil is warm enough
Watermelons like it hot. Seeds will not germinate if the soil temperature is below 60°F and they would prefer yours to be 70°F. If you are growing seedlings indoors, consider using a heating mat to keep them warm.
If you’re not sure how warm your floor is, measure its temperature. You can use a meat thermometer to check the temperature in your soil if it drops to 50°F or get a soil thermometer.
Get the Taylor Precision Products Soil Test Thermometer on Amazon for $11
Sow seeds far apart
Watermelons grow on vines 3 to 4 feet long, while vines may need to spread 10 feet or more for taller watermelons.
Little space? You can grow watermelons on a low, sturdy trellis like an A-frame design that can also be used to grow cucumbers. Plant watermelon seeds about half an inch deep in the soil. When planting watermelon seedlings, remove the plastic pot and plant them as deep in the soil as they were in the pot; do not heap the dirt higher on the trunk. When planting your watermelons in a row, place two to three seeds about 2 feet apart and space rows at least 5 to 6 feet apart.
You can also plant watermelon seeds on mounds in mounds of soil about four to eight inches high, about a foot wide, and spaced four to five feet apart. Expect six seeds per hill. A few weeks after planting, when the plants have two or three leaves, thin them out to two plants per hill.
Support melons growing on a trellis by placing a sling or support underneath and attaching it directly to the trellis—not to another part of the vine. You can use old stockings or onion sacks, or get a pack of melon hammock nets to keep your little watermelons growing safely.
Watermelons need a lot of water to thrive. Once settled in the soil, make sure the cantaloupe gets 1 to 2 inches of water per week – about half an hour at a time. Use a rain gauge to check how much water your watermelon plants are getting.
It’s better to water them in one long, slow session each week rather than in daily doses. The water penetrates deeper into the soil where the roots are and the leaves stay drier longer. Water early in the morning to allow the leaves to dry out in the sun. Watermelon plants tend to get diseases when their leaves get wet.
If you’re going on vacation but want to grow your garden, try an app-connected smart hose timer. The timer connects to a garden hose that can be connected to a drip irrigation system or sprinkler head for remote water management. If you have an underground irrigation system, a smart sprinkler controller effectively works like a hose timer, allowing you to set watering schedules, turn sprinklers on and off, and overall remote control of your sprinkler system. Intelligent lawn watering devices save you time, money and prevent overwatering.
Stop watering your watermelons about two weeks before you expect to ripen them. Too much water just before harvest time can cause the watermelon to burst open while still hanging on the vine—and you don’t want to share your harvest with wasps and slugs. Shut off the hose unless your area is suffering from a drought.
How to harvest watermelons
Unlike cantaloupes, watermelons don’t “slip” (fall off the stalk) when ripe. Instead, look for these signs that your watermelon is ready to pick:
- The “ground patch” where the melon sits on the ground turns yellow.
- The vine tendrils near the fruit dry up and turn brown.
- The skin of the watermelon looks less shiny and more dull/matte
Put on your gardening gloves and use pruning shears to cut the watermelon off the vine. Don’t hesitate! Watermelons will rot if you leave them on the ground – and many pests like ripe watermelons, including coyotes.
Eat your watermelon right away or refrigerate it for up to 2 weeks.
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