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Let's Grow Some Watermelon!


Q. Mike: You have given me good advice in the past; now I want to ask about growing watermelons. There is a section of garden not yet planted. What needs to be done to the soil to accommodate watermelons? When should they be planted? Oh, and thanks for a wonderful program! I try to organize my ironing around your show so I can be productive and listen to you at the same time!
    ---Cathy; just outside of Royersford PA
A. Hey! Listening to me IS productive; its gonna get you watermelon, isn't it? Anyway, "when should they be planted?" Not early! One of their primary needs is a very warm soil, and plants that go out too early in the season will simply not prosper. You should always wait until at least two weeks AFTER your zone's 'last average frost date', which would be around June 1st in your Philadelphia area and thereabouts. So, as we post this question mid-June you're fine for this year; in fact, we're now into the "Time's a wasting!" window. (More on that in a minute.)

Here's the basic plan:

Remove any mulch from your raised beds early in the season so the sun can hit the soil directly. Then, a couple weeks before planting time, cover the soil with black plastic to hold and trap the heat (6 mil thick to be specific, says melon maven Amy Goldman, authoress of the beautiful and informative "Melons for the Passionate Grower"; Artisan Books; 2002). Then plant the vines into slits cut in the black plastic AND protect the young transplants with floating row covers the first few weeks, when nights can still get chilly.

Back when I was Editor of ORGANIC GARDENING magazine, Dr. Wilton Cook, a Professor of Horticulture at Clemson University explained that growers just about everywhere—even the Deep South—can benefit from black plastic. He said it ripens the melons up a good week earlier and greatly increases your yield, no matter where you are. Same with those spun polyester row covers; a 1990 Kansas State University study found that using these sheer, heat-trapping blankets early in the season greatly improved survival and yields.

Growers in normal climes—that is, not the deep South—should stick with those cute-as-the dickens round "icebox" 5 to 12 pound melons, like the classics "Sugar Baby" and "Garden Baby" (which I have personally grown successfully in my rural Pennsylvania garden.) These very sweet cuties typically ripen up their first fruits 75 to 80 days after planting, come in red and yellow-fleshed varieties and have a huge range of rind colors.

If you live in a really dicey, short-season climate (or want to try and get a little crop in this season of 2008) look for varieties that can ripen their first fruits in the dead absolute minimum 65 to 75 days, like "Sugar Baby" and "Yellow Doll"; use black plastic; and maybe light a candle to the Blessed Mother. If even your summertime nights are chilly, try "Black Tail Mountain", a fast-to-mature, cold-tolerant icebox type bred by noted seed saved Glenn Drowns, whose Northern Idaho nights dip into the 40s in summer. Brrrrr.

Everyone needs to be careful when they transplant their precious babies into the garden, as watermelon starts are very temperamental. Plant them at just three or four weeks of age, not the six or more weeks recommended for most other garden goodies; and try to keep all the soil around the roots. (This is a good place for peat pots, where you put the decomposable pot and all into the ground.) If you have a long enough season, go ahead and plant the seeds directly in the ground—but only after the soil has warmed up nicely.

If you DO live down South, you can try and grow the real monsters (the ones you need to drop into a stream to chill down) like Georgia Rattlesnake and Carolina Cross. Just be warned that you need at least 100 hot and sunny summer days to ripen these 30 to 100-pound fruits; and you'll only get one or two per plant, versus 3 to 5 of the icebox size. And the icebox types require a lot less garden space; especially if you trellis the vines upward (which also helps keep the fruits nice and clean).

And of course I have to mention THE classic variety, "Moon and Stars", a medium sized (20 to 30 pound) 100-day heirloom that develops celestial designs on its rind as it grows. It's the absolute coolest kid on the watermelon block.

All watermelons need a loose, well-draining, naturally-rich soil. They're pretty heavy feeders, so even growers who aren't organic add huge amounts of compost to the bed before planting. Midseason boosts with more compost, compost tea, a fish and seaweed mix or other gentle organic fertilizer are highly recommended. True to their name, they like a lot of water, but not on their leaves; this is a good place for soaker hoses or drip irrigation. Promptly remove any discolored leaves you see, as well as any fruits that are deformed or that seem too small.

That's pretty much it. Give your plants plenty of food, water, heat, room and love and you may well wind up facing that most perplexing of all garden problems: How do I tell when the furschluginner things are ripe??? Which brings us to….

Q. Mike: How do you determine when to harvest watermelons? Last season was my first time planting any, and they flourished beyond my expectations! The seed packet said they needed a 90-day growing season, but my wife picked one right about day 90, and it was mostly white inside, with just a little pink fruit. How can we do better in the future?
    ---Greg in Springfield, MO
A. There is much lore about thumping, plunking, tapping and pinking, but those abusive sounds aren't always reliable, Greg. First, you're right to keep track of the number of days the plants have been in the ground. As you approach that date, watch for:
  • The development of a 'couche', or yellowish ground spot where the melon sits;
  • A loss of sheen on the rind; and—most reliable for my money—
  • The browning of the tendril closest to the fruit.
The correct number of days + a nice yellow couche + a dull rind + a brown tendril next door almost always = a nice ripe melon. But if thump you must, an expert once told me "it should sound like you're thumping your bare chest, not your head."

That's YOUR head, Greg—not mine….

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