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The Great Watermelon Challenge

Tips on growing watermelon in North Dakota

WatermelonOne of the joys of summer is biting into a cold, crisp slice of watermelon. Juices drip down your cheeks and then you get to spit the seeds out. Delicious!

The watermelons we enjoy here in North Dakota were likely grown hundreds of miles south of here. Our growing season is too short and too cold.

That being said, it’s fun to grow watermelons. It may be a challenge, but it certainly is not impossible.

Start with an early ripening variety. North Dakota State University and its team of 250+ gardeners evaluate vegetable varieties every year. One of the best performers is ‘Sweet Dakota Rose’, which was developed here in our state. Some of our evaluators say it is the best watermelon they have ever eaten. The melons have attractive green stripes and grow up to 20 pounds. The flesh is very flavorful. Yields are good but not reliable, especially in the far north (this unreliability holds true for all melon varieties).

Start your seeds indoors. Melon transplants are usually grown in peat pots to reduce transplanting shock. Place three seeds in each pot and give them temps in the 80s to get them germinated. Heating mats help. Temps in the 70s are fine after germination. Vines growing with and without clear plastic mulchMove the transplants to the garden after the soil is warm (first week of June) and while the transplants are only 3–4 weeks old.

Melons need heat and plastic mulch can make a big difference. Black plastic mulch is most widely available and will raise soil temperatures 5°F versus bare ground.

You can generate even more heat by using clear plastic mulch (8–14°F). Vines grown over clear plastic mulch will bloom faster and produce earlier and higher yields compared to vines grown without mulch (see photo). Clear plastic is not widely used in the USA because weeds grow under it. But we need as much heat as possible and weeds in well-managed gardens are usually a minor problem. Herbicides can be used to prevent weeds, too.

The latest mulch technology is green infrared-transmitting (IRT) “solar” mulch. It blocks out visible light, thereby suppressing weeds, AND it allows infrared light to pass through, generating more heat than black plastic mulch. Increases of 8–10°F over bare soil are reported.

Melons have been shown to respond to blue plastic mulch as well. Studies in Pennsylvania show yield increases of 20–35% using blue plastic over black plastic. Blue plastic suppresses weeds and produces slightly higher soil temperatures than black plastic. The reflected blue light seems to enhance vine development, too.


Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Published in the NDSU Yard & Garden Report, August 18, 2014. Photos were made available under Creative Commons licenses specified by the photographers: Rafael Moreno and Tom Kalb, NDSU.


Orzolek, M.D. and W.J. Lamont, Jr.. 2014. Summary and recommendations for the use of mulch color in vegetable production. Pennsylvania State University: State College.

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