How to Grow: Watermelons

Yes, you can grow watermelons (Citrullus lanantus) in our climate and they’re worth the effort. I’ve grown the small round, ice-box types and kids and adults love to crack them open, munch on the sweet juicy flesh, and have seed splitting contests.

Watermelon growing in a field

While watermelons are mostly, water, they do contains vitamins such as A, B, and C and high amounts of the cancer-fighting anti-oxidant lycopene. Varieties are either oval or round with pink, yellow, orange or red flesh and seeded or seedless.

When to Plant

Watermelons like the heat, so wait until 2 weeks after your last frost date (May or June), to plant seeds and seedlings.

Where to Plant

Watermelon plants need full sun to fruit. They also vine or “run”, like pumpkins and winter squash, so give them room to ramble. I like to grow watermelons on the edge of the garden and let the fruits vine into the lawn. I just mow around them and it reduces the amount of lawn mowing and gives me more space in my garden to plant other vegetables. Plant flowers near by to attract bees to pollinate the flowers.

How to Plant

Amend the soil well with compost before planting. Get watermelons off to a good start by planting them on raised beds covered in black or dark green plastic. The raised beds warm up and dry out faster in spring allowing you to plant sooner. The plastic laid on the bed two weeks before planting, preheats the soil. Poke holes in the plastic every 12 inches and plant three seeds or one seedling per hole. Thin the seeds to the strongest one per hole after they germinate.

Care and Maintenance

Watermelons need consistent water and fertility to produce fruits. Add at least 1 inch of water a week — more during hot, dry weather. If you aren’t using plastic mulch, hand weed around plants. Add a small handful of an organic fertilizer, such as 5-5-5 around each plant at transplant time, when the vines start to run, and at first flowering. Towards fall, as the nights dip into the 50Fs, help the existing fruits ripen by cutting off the tips of the vines, new flowers, and any young fruit. This will send more energy into the existing fruits. Place the existing watermelons on a piece of wood or pail to keep the fruits off the ground where diseases and critters might attack.

Watermelons are attacked by the same pests that love melons. See the melons section for tips on controlling these pests and diseases.

Harvest

Knowing when to harvest watermelons can be tricky. If you pick them too early, they won’t continue to ripen off the vine. If you wait too late, the flesh becomes mealy textured. Some of the techniques to know when to pick require some experience. Do a little trial and error and make notes on what works.

Check the curly tendril (curly cue) on the stem closest to the ripening watermelon. When it turns brown, the watermelon is ripe. Check the underside of the watermelon. When the spot where it sits on the ground turns from white to yellow, the fruit is ripe. Finally, this one takes some practice, thump the watermelon with your thumb. It’s ripe when you hear a dull thump sound versus a tinny sound.

Additional Information

In general, the icebox-shaped watermelon varieties are better for our climate because most mature faster than the oblong-shaped ones. Icebox types average 4 to 8 pounds per fruit, whereas oval-shaped varieties can grow to 25 pounds per fruit. ‘Sugar Baby’ is a tried-and-true icebox type with sweet red flesh. ‘Baby Doll Hybrid’ is an icebox type with yellow flesh. ‘New Orchid Hybrid’ is an orange fleshed icebox type. ‘Moon and Stars’ is a unique oval, red fleshed heirloom with dark green skin and yellow markings that resemble a moon with stars.

Text excepted from the Northeast Vegetable and Fruit Gardening book.