Gardening Tips: Growing, Harvesting, and Enjoying Watermelons

Watermelons are a favorite vegetable for many gardeners. They grow on fast-growing vines that cover a large area of the garden. At this time of year, watermelons should be at or close to maturity, depending on planting date and management or environmental factors (such as how much rain you got compared to other parts of the county).

Watermelon is related to cucumber, pumpkin, and squash. It shares many of the same pests, though they don’t necessarily affect each plant in the same way.

Watermelons seem a bit more pest-resistant than those other family members in many cases. Insect problems are limited mainly to aphids and cucumber beetles, and diseases include powdery mildew and various wilt and various leaf spot diseases.

Aphids are small, soft-bodied insects, usually yellow, green, or white. They are found on the underside of leaves, and secrete a substance called honeydew that makes the leaves appear shiny and wet. Aphids generally do little direct damage to watermelons, although they may carry viruses that can be very damaging indirectly. They should be sprayed with insecticidal soap. It is important when spraying to cover the underside of the leaves where the insects are found. Cucumber beetles have black and yellow stripes or spots. They also may carry diseases, and the cucumber beetle larvae can damage the plants by boring into the stem, causing the plant to die. Cucumber beetles can be treated with bifenthrin.

Top photo: Watermelon leaves, stem, and flowers. Photo by Eiku, CC BY-SA 3.0.  Bottom photo: Aphids suck sap from the underside of leaves. Right: Growing watermelons on a trellis in a small garden.

Powdery mildew is a disease that causes white fungal patches on the leaves of watermelon vines. The fungus spreads and eventually leaves die, causing the fruit to be exposed and ripen prematurely. Control for this is to plant resistant varieties and to avoid watering the leaves of the plant directly, especially during the day.

There are a number of other diseases that may cause wilt or leaf spots that are a large concern for commercial growers, but are generally not a problem for home gardeners. If you do have a problem with watermelons, bring a sample to the cooperative extension office for identification.

Left: Slices of juicy watermelon are the perfect snack on a hot summer day. Below: Watermelon on the vine, covering a large part of the garden. Photo by F. & K. Starr, CC BY 3.0

Since watermelons are 95% water, they need adequate rainfall or irrigation to mature properly. Lack of water can stress the plants, which will make them more susceptible to the problems listed above. A good rule of thumb is to provide the plants with about an inch of water every week. They also need a good dose of 10-10-10 fertilizer, and some supplemental calcium to ensure they don’t succumb to blossom end rot.

Luckily, weeds are not usually an issue for home gardeners growing watermelons. Many vegetables can be overtaken by weeds before even getting started, but watermelon vines grow so quickly they normally cover up weeds that would compete with less vigorous plants.

Watermelons are generally ready to harvest once the stem begins to turn brown and twist, and the white spot on the bottom of the melon where it contacts the grounds has turned to yellow.

Matthew Stevens is the County Extension Director and Horticulture Agent for North Carolina Cooperative Extension’s Pitt County Center. If you have questions about this article or gardening in general, please contact the Pitt County Extension Master Gardeners at [email protected] or 252-902-1705.