Growing watermelon vertically on a trellis is an effective strategy for cultivating this sprawling vine crop in smaller spaces, especially in compact urban gardens. This method utilizes vertical space instead of ground coverage. Elevating the vines also increases air circulation around the foliage and fruit, helping to reduce the pressure from common fungal diseases and ground-dwelling pests.
Selecting the Right Foundation
Selecting the right plant variety and support structure is crucial for a successful vertical watermelon garden. It is important to choose “icebox” or “mini” varieties, as their smaller fruit size is manageable for a trellis system. Varieties like ‘Sugar Baby,’ ‘Yellow Doll,’ or ‘Golden Midget’ typically produce melons weighing between 3 and 12 pounds. Gardeners should avoid planting large, traditional varieties that produce 20 to 30-pound fruit, as supporting this weight vertically is difficult and risky. The trellis must be strong and installed before the plants begin to vine, since a mature plant and its fruit can collectively weigh 50 to 100 pounds. Suitable options for a stable foundation include sturdy materials such as cattle fencing, heavy-duty wire mesh, or a well-anchored wooden A-frame.
Planting and Initial Training
Watermelon plants thrive in rich, well-draining soil that has been amended with compost or well-rotted manure, as they are heavy feeders. For vertical growing, plants can be spaced slightly closer than they would be in a conventional garden, typically about 18 to 24 inches apart. This closer spacing works because the vines are directed upward rather than allowed to sprawl across the ground.
Once the young vines begin to grow, they must be gently guided toward the vertical support structure. Watermelon vines do not naturally climb a trellis with sufficient grip to support the heavy fruit. The coiling tendrils provide some attachment, but they are not reliable enough to secure the main vine. To prevent the vine from falling or being damaged by wind, the main stem should be loosely secured to the trellis every 12 to 18 inches using soft material. Strips of cloth, old hosiery, or specialized garden tape are excellent for creating a loose figure-eight tie that holds the vine without restricting its growth.
Managing Vine Growth and Fruit Support
Managing vine growth is necessary to ensure the plant’s energy is directed toward fruit development and that air circulation remains optimal. Watermelon plants produce a single main vine and numerous lateral side shoots that grow from the leaf axils along the main stem. These side shoots should be “pinched back” or removed entirely to focus the plant’s resources on the main vine and the developing fruit. This strategic pruning also helps to prevent an overly dense canopy, which can trap moisture and encourage disease.
It is recommended to limit the number of developing watermelons to two or three per main vine. Removing excess flowers and smaller, less vigorous fruit allows the plant to channel energy into growing high-quality, full-sized melons. As the watermelons grow to the size of a tennis ball or softball, they must be supported to prevent their weight from snapping the delicate vine stem. This support is achieved by creating a sling or hammock for each fruit. Slings can be fashioned from repurposed materials such as old pantyhose, sections of mesh netting, or stretchy fabric. The sling must be securely tied directly to the trellis structure itself, not to the vine, ensuring the weight is borne entirely by the support system.
Water, Nutrients, and Harvesting
Vertically grown watermelons require consistent and deep watering, often more frequently than ground-grown plants, due to increased exposure to sun and wind. Deep watering encourages the development of a strong root system, which is important for supporting the heavy plant and fruit load. The plant’s nutritional needs also change significantly throughout the growing season.
During the initial growth phase, a balanced fertilizer, such as a 10-10-10 ratio, supports vigorous vine development. Once the plant begins to flower and set fruit, the fertilizer regimen should switch to a formula that is lower in nitrogen and higher in phosphorus and potassium, such as a 5-10-10 or 5-10-15 blend. This high-potassium feeding contributes directly to the sweetness and overall quality of the fruit.
Determining when a trellised watermelon is ripe relies on a few visual cues. The most reliable indicator is the tendril closest to the fruit stem; when the melon is ripe, this tendril will dry out and turn brown. Additionally, the small patch of the melon resting in the sling, sometimes referred to as the “ground spot,” will change from a pale white or green color to a distinct creamy yellow.