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Plant of the Month: Watermelons

  • You can start your seeds at any point in the year as long as your greenhouse temperature and lighting is controlled.
  • You want the temperature of the greenhouse to be between 85 and 90 degrees fahrenheit during the day and 65-72 degrees fahrenheit at night.
  • When starting your seeds plant them in 2 inch deep seed starting containers with soil that has been heated to at least 85 degrees fahrenheit.
  • After germination, when the first two leaves appear (usually 3-12 days) you may transplant your watermelon seedlings into containers that hold at least 5 gallons of soil.
  • Provide a sturdy trellis for the watermelon plants to climb.
  • Approximately 5-10 days after germination the first vine should appear from your watermelon seedlings, and about a month after that you should see several more.
  • About two weeks after all the vines (runners) appear you will start to see flowers, both male and female. The male flowers develop first and only last a day so make sure you populate your greenhouse with pollinators ( the best and least expensive are bumble bees) if you haven’t already.
  • When the female flowers are sufficiently pollinated fruit will begin to grow beneath the blossom.
  • The fruit takes around a month to fully develop
  • Then you enjoy!

 There are a few things you want to keep in mind when planting watermelons.

  • Make sure they have at least 4-6 feet of space inside the greenhouse.
  • Don’t plant different varieties of watermelon too close to each other as pollinators might cross pollinate. (Example: if you have seedless and traditional watermelon plants near one another you might get a few seeds in your seedless due to cross pollination) Cross Pollination may still happen but the further away they are the less likely it is.
  • Don’t plant your watermelon plants near roses or mustard greens. Aphids love all three of these plants and you are less likely to get an infestation on all of them if they are further apart. (see our blog “The Dirt on Beneficial Greenhouse Bugs” for more information on aphid infestations)

Want to pick out the best watermelon to impress your friends?

  • The best watermelon will be firm and symmetrical.
  • It will be dark green and dull rather than shiny in color.
  • It will be heavier than the rest of the melons of the same size (this means it has more juice in it)

If your market doesn’t have watermelons year round it might be time to talk to your local produce manager about fresh local watermelons. Make sure to bring a sample with you as the best sales tool for any crop is the fruit!

Happy Growing, and Happy Summer!