Learning how to grow watermelon in the winter can prove to be a difficult task, but it is not an insurmountable one. While watermelons prefer moist heat as is common in Southern areas, Northern winter gardeners who take sufficient care of their watermelon crops can reap bountiful, early harvests.
To grow watermelon in the winter, you’ll need:
- Watermelon seeds
- Individual peat pots
- Potting soil
- Roll of black plastic
Instructions for how to grow watermelon in the winter:
- Fill the individual peat pots with potting soil indoors, toward the end of winter. Leave about a half-inch at the top of each pot.
- Plant the seeds about one inch deep. It is best to plant two or three seeds per pot, especially when first learning how to grow watermelon in winter. A more experienced gardener might be able to plant more seeds of some varieties and transplant them with greater luck.
- Use a high-nitrogen fertilizer until flowers form. Then, switch over to a fertilizer with high amounts of phosphorous and potassium.
- Add water frequently, as watermelon plants need to be kept in moist soil. Part of knowing how to grow watermelon in the winter is being careful not to over-water, as this can create mildew and rot.
- Transplant the plants directly in their containers to hills in a well-draining outdoor garden bed (sandy loam is best) when they reach about six inches in length. This is the tricky part, as watermelon does best when planted once, in the heat, outdoors. Farmers typically plant transplants, though; that is how to grow watermelon in the winter.
- Cover the plants with plastic until the weather is sufficiently warm for them to thrive and the danger of frost is past. Black plastic is a necessity when growing watermelon in winter, as it promotes earliness by warming the soil underneath it. A Kentucky State University article suggests using hay and newspaper as an alternative to plastic.
- Use miniature greenhouses made of gallon milk jugs on cool nights to protect the seedlings, even after you have removed the plastic sheeting. These miniature greenhouses, sometimes called “hot caps,” can often save tender seedlings from surprise frosts.
- The watermelons should be ready to harvest in about 90 days from their original planting. Length of time from planting to harvest depends upon the variety of watermelon.
To test for ripeness, rap your knuckles on the fruit. A dull sound means it is ready to harvest, while a sharp sound indicates the fruit is still green.
Do not start the seeds too early; large watermelon seedlings do not transplant well, according to the University of Illinois Extension.
According to UC Davis Vegetable Research and Information Center, you should use a knife to sever the fruit from the vine, rather than pulling the fruit off manually.