Optimal conditions to grow watermelons

(Question)

I would like to grow watermelons in my backyard this summer. What can I do to ensure they have the best chance of growing?

What type of soil is best? Direct sunlight, partial, or shade? Lots of water or only what comes down from the sky?

I live just north of Steeles Avenue at Yonge Street, in Vaughan. The soil is often very dry, especially in June / July.

Thanks, Michael.

(Answer)

Hello Michael. Watermelons grow best in hot, humid weather but plenty of short season varieties are available for Canadian Gardeners. They do require a long growing season though so to get a good head start you can start your own from seed. Alternatively started plants can be purchased from garden centres or nurseries. If you are starting your own from seed how to go about it is in the next paragraph. If you plan on buying already started plants then skip to the third paragraph for more information.

So, starting from seed: Seed melons indoors about a month before you plan to transplant outdoors which will be a week or so after your frost free date. To be safe plant in the first week of May to plant out in first weeks of June. The most practical advice can be found in The Organic Home Garden by Patrick Lima and John Scanlon. Here is what they have to say. “Sow the seeds in individual peat pots, do not crowd together because melons are sensitive to root stress and may die if disturbed so put 2 or 3 seeds in a 4 inch (10 cm) pot. To germinate melon seeds need the extra warmth provided by heating cables, a radiator or proximity to the stove during a baking session. Ordinary room temperatures leave them cold and dormant. On sunny days put your seeded pots covered in clear plastic to sit in front of a south-facing window. Once the seeds have sprouted keep in a sunny space. When the young vines are working on their second leaf cut all but the strongest one per pot – scissor away do not pull out to minimize damaging the roots of the one left to grow”.

Transplanting outdoors: Lima and Scanlon note that “melons are probably the most cold sensitive crop you’ll grow and a chilly spell may stress the vines beyond recovery. With an ear to the long-range forecast, delay transplanting until summery weather has settled in for sure, usually a week or two after tomatoes and peppers are in the ground.” When transplanting outdoors you will need a spot in full sun. Water melons need plenty of sunshine, so do not plant them with or near other tall-growing vegetables.

The ideal melon soil is light, warm, well drained and fertile. I would add a generous amount of compost to your soil. Lima and Scanlan add “a balanced natural fertilizer, turned in just before transplanting, or stirred into the holes, keeps the hungry vines well fed.” One extra precaution you could take is to cover the melon bed with a top-sheet of floating row cover, a translucent spun-fibre fabric that lies lightly over the seedlings. Lima and Scanlan do this and report that their “vines run riot under the cloth, which must be lifted when yellow blossoms appear to let in pollinators, unless you hand pollinate.”

“Melon flowers are either male or female. Female flowers are backed by a small round swelling, a tiny embryonic fruit; male flowers are attached to the vine by only a thin stem. For fruit to form, pollen must move from male to female, a task usually performed by bees and other flying insects. In short season areas (like ours) it is important that the first female flowers open are in fact pollinated since these will be the melons most likely to ripen before frost. Flowers stay open for only one day and if no bees happen by you can say good-bye to that fruit. Sometimes one has to play matchmaker, using a small water colour brush to transfer pollen. A random flight with the brush from male to female blossoms should do it, even though melon pollen is so fine you may wonder if you are accomplishing anything. With luck, bees will discover the flowering vines and return on a daily pollen run and you can let nature take its course.”

“Once pollinated the little pea-sized melons begin to swell quickly under the summer sun and the thirsty vines needs a lot of water to plump their fruit. A deep weekly drink is better than frequent shallow showers; sun warmed water is preferable to icy cold. To reduce the risk of fungus, water in the morning so that vines dry by nightfall”. Lima and Scanlan say that “melons are one crop we never mulch (a moisture holding layer of hay or grass may keep the earth too cool for them) but growth is usually dense enough to shade the ground from the sun’s full drying force”. Keep plenty of water coming during the growth and early fruiting stages but to intensify flavour allow the ground to dry out a bit once the fruit is ripening.

When to harvest? Lima and Scanlan refer to “Mark Twain, watermelon aficionado, once instructed gardeners in a game of musical melons to test for maturity. Pink, pank, punk: tapped gently, a watermelon will sing a descending scale as it ripens. Punk – low-toned, somewhat hollow, is the sound of ripeness. If you are tone deaf a watermelon normally has a light coloured patch on the rind where it touches the ground that changes from white to yellow as the fruit matures. If the melon’s stem has withered altogether pick it as no more juice will flow to that fruit. As a rule if all signs and sounds say “ripe”, wait a day or  two more. Watermelons, unlike bananas, apples, pears, and cantaloupes do not manufacture any more sugar after they are picked.”

I hope all this helps Michael. By the way, for good companion plants Watermelons are good to interplant with potatoes, particularly if the potatoes are mulched with straw. Good luck for a bumper harvest!