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Growing Watermelons
by Leonard Perry
by Leonard Perry


In extension I serve as an advisor and consultant to the greenhouse and nursery industry, primarily in Vermont but throughout the region and beyond as well.

I give presentations on my research to the industry, and to home groups. In Research, my focus is "herbaceous perennial production systems".

His website is at  Leonards zone of gardening: home with my trials, generally USDA 4a. Campus in Burlington is 5.

May 19, 2013

Think of watermelons and the images that come to mind for many are warm summer days, picnics, barbeques, and outings with family and friends. Although a warm climate crop, there are watermelons you can grow in the north. For the best success, follow a few simple steps, beginning in May.

Most gardeners start watermelons from seeds, so the first step is to choose the right cultivars (cultivated varieties). There are 4 main types of watermelons. “Picnic” ones are the largest, ranging from 15 to 50 pounds, and with shapes varying from rounded to oblong. “Icebox” ones are smaller, 5 to 15 pounds, and rounded—thus fitting better in refrigerators, known in the past and still by many as “iceboxes”. Newer ones are seedless, in varying shapes and from 10 to 20 pounds. Seedless ones came about in the early 1990’s, and today half of all watermelons sold in stores are seedless. Then there are those with yellow or orange flesh inside. Expect one or two fruits per plant, with more for seedless selections.

Watermelons need a long growing season, for most cultivars, of 80 to 100 days. If you’re gardening in a cooler climate with shorter growing season, consider selections that mature 75 to 80 days from transplanting. ‘Sugar Baby’ is a standard of the small watermelons with rounded fruit, only 6 to 8 inches wide and 8 to 10 pounds, and a dark green rind. ‘Sweet Beauty’ has smaller, oblong fruit in green with darker stripes. ‘Sweet Favorite’ has slightly larger fruit than ‘Sugar Baby’, oblong and bright green with dark stripes. Similar only with rounded fruit is the hybrid ‘Starlight’.

For unique colors, ‘Sunshine’ is a small hybrid similar in size to ‘Sugar Baby’ but with yellow flesh, and light green rind with dark stripes. ‘Sorbet Swirl’ is a newer hybrid, with oval fruit to about 10 pounds, and flesh in swirls of red and yellow. ‘Faerie’ has small fruit of 4 to 6 pounds with an oblong shape, red flesh, and yellow rind; and, they may mature in about 60 days.

Since watermelons like warm to hot climates, you’ll want to wait until the soil reaches about 70 degrees (F) before sowing or planting out. Since in the north this may be early summer, you can get a jump on the season a couple of ways. Sow seeds indoors mid to late May in most areas-- 2 to 3 weeks before planting out. To warm the soil where you’ll plant, cover your garden soil outside, about the same time as you sow indoors, with black plastic.

If starting seeds indoors, use peat pots that you can plant directly in the ground. Sow a couple seeds per pot, in a soilless medium. Don’t start too soon, as plants will get too large and their growth will be set back at transplanting. Place pots in a sunny window, or under lights (on 16 hours a day) on a heating mat which you can buy in garden stores and online. Ideally, soil temperatures in your pots should be 75 to 80 degrees. Once seeds germinate, keep watered, and as plants start to form leaves give a half-strength solution of fertilizer of your choice.

Before planting outside, work plenty of compost or composted cow manure into the soil, and add a balanced fertilizer such as 5-3-4 or 10-10-10 (4 or 3 pounds, respectively, per 100 square feet). If sowing seeds directly, sow 2 or 3 seeds in a shallow mound. Space the mounds (or plants if planting seedlings) 3 to 4 feet apart, in rows 8 feet apart. The smaller melons can be grown closer—2 feet apart in rows 4 feet apart. To minimize any soil, pest, or disease problems, don’t plant watermelons in the same bed or space where you had cucumbers, melons, or squash in the previous year or two.

Vines of many cultivars can reach 20 feet long, so need plenty of space. There are some newer cultivars such as ‘Sugar Baby’ with vines only 3 to 4 feet long, and ‘Sweet Beauty’ or ‘Faerie’ with vines 9 to 10 feet long. Look for such shorter vining selections if you’re short on space. Or, consider growing up a “sturdy” trellis, as made from pipes or 2x4 lumber. For such upright vines, support the heavy fruit with slings made from netting or cloth.

Once planted outside and watered, cover with a lightweight row cover fabric which you can find in many garden stores. This has two purposes—to help retain some soil heat, and to keep cucumber beetles and vine borer moths away. Make sure to uncover plants, though, when flowering so honey bees and other insects can pollinate them.

Plants need at least an inch of water a week, from you if not from rain. You’ll want to water with fertilizer according to the label, or “side dress” dry fertilizer around plants, when vines start growing and when fruits are maturing. Use a dry fertilizer such as 5-3-4 analysis at the rate of 2 pounds per 100 square feet of garden area at each application. When fruits start to mature, use less water so melons will become sweeter.

There are 3 ways to check if your watermelon is ripe. When the curly tendril closest to the fruit stem turns brown and dries up, the watermelon “may” be ripe, however, for some cultivars this happens a week before fruit are fully ripe. Most common is to tap or thump the melon with your fingers, a ripe fruit making a soft hollow sound or “thunk” instead of a higher-pitched “ping”. Perhaps best is to check the bottom of the fruit where it rests on the ground. This area turns from almost white to yellowish when fruit are ripe. Ripe fruits lose their slick or powdery surface, taking on a dull appearance.

Watermelons are best chilled and eaten fresh. Cut, they’ll store up to 4 days wrapped in plastic in the refrigerator. Uncut, they’ll store 10 days or so.

Watermelons are great to quench summer thirst, being up to 92 percent water. They are healthful, being rich in vitamins A, B6, and C plus other beneficial minerals and compounds. They’re rich in lycopene, an antioxidant that may reduce the risk of some diseases such as prostate and breast cancers, heart disease, and asthma. An amino acid in watermelon (citrulline) may help boost the immune system. Studies have shown that watermelon can protect against vision loss, even more so than eating carrots. These possible benefits do not substitute, of course, for medical advice from your doctor if you have such conditions.

Each year the National Garden Bureau chooses a flower and vegetable to feature, with 2013 being the Year of the Watermelon. More information on this crop, as well as others from the past, can be found on their website (

photo courtesy NGB

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