Botanically watermelon is a warm-season fruit, though as a member of the cucurbit family of gourds, it is grown and harvested as a vegetable.
Most believe watermelon originated in the deserts and semitropical regions of southern Africa. Hieroglyphics found on the walls of ancient Egyptian buildings depict the first watermelon harvest occurring nearly 5,000 years ago.
Today, watermelon is grown around the world and its composition is up to 95% water, hence its name. Rinds, whether solid in color or striped, look hardy but are quite fragile and require picking by hand at harvest.
Interestingly, watermelon is completely edible: the flesh is sweet and juicy, the seeds can be roasted, and the rind can be used for making preserves, pickles, and relish.
Types & Varieties
There are several hundred varieties of watermelon grown in the United States and Mexico. The most common are Seeded, Seedless, Mini, Yellow, and Orange, with many popular cultivars within each category. Rind and flesh colors can vary, as well as both size and shape.
Top growing regions in the United States are Florida, Georgia, California, and Texas. Prevalent seeded varieties grown in these states and elsewhere include Calsweet, Fiesta, Royal Sweet, Sangria, Sultan, and Tiger.
Seedless varieties, which continue to gain in popularity, include Cotton Candy, Crimson Trio, Fandango, Fire Cracker, Genesis, King of Hearts, Nova, Scarlet Trio, Super Cool, Summersweet, Sweet Slice, and Tycoon.
Mickeylee, Palm Melon, Precious Perfection, Precious Petite, Solitaire, and Sugar Baby are popular miniature watermelon varieties. Crimson Sweet and Charleston Grey varieties produce larger, more traditional melons in both Florida and Georgia, along with Florida Giant and Sweet Favorite in Georgia.
Lesser known though gaining converts are yellow-fleshed varieties, which include the aptly-named Summer Gold, Yellow Baby, and Yellow Doll. Gold Strike is an orange-fleshed variety.
Watermelon should be planted after the danger of frost has passed and soil is warm. Plants tend to grow best in air temperatures between 70°F and 85°F and soil temperatures between 60°F and 65°F. Row covers and black plastic mulch can maintain soil warmth.
Sandy loam is optimal, providing good drainage and nutrients. Growing on ridges will help keep roots dry. Vines require considerable space, so plantings are typically kept 5 or 6 feet apart, with 7 to 10 feet between rows. Crops can be direct seeded or transplanted.
Watermelon should be picked at full maturity (it does not ripen after harvest), when stripes have darkened and sugar content has reached about 10%.
Overly ripe melons will turn mealy with little flavor. Melons must be protected to prevent sunburn. A symmetrical appearance, waxy surface, and lack of bruising are all signs of good quality.
Pests & Diseases
Cucumber beetles attack plants, feeding on leaves and stems, but should not be confused with lady beetles, a beneficial insect. Both striped and spotted beetles can cause damage; striped cucumber beetles can transmit diseases like bacterial wilt. The best prevention is to remove weeds or planting a “trap crop” to attract the insects away from melon plants.
Aphids cause leaves to curl and can prevent plants from growing to full size. Melon aphids, specifically, can be identified by their long legs, antennae, and range of color from yellow-green to greenish-black.
Honeydew waste secretions can cause fungal growth and attract other insects. Natural aphid enemies—such as parasitic wasps or lady beetles—can help lower populations.
Rindworms include several caterpillar species such as beet armyworm, cabbage lopper, cutworms, and tobacco budworms. They feed on stems and foliage but the more costly damage is to rinds, which may be difficult to spot. Other insect dangers include leafminers, spider mites, squash bugs, stink bugs, thrips, vine borers, and whiteflies.
Anthracnose creates small, brown-black spots on leaves and fruit. Prevention includes seed treatment, crop rotation, and fungicide applications.
Downy mildew is caused by an airborne fungus and exacerbated by heavy rains. Yellow-brown spots appear on the leaf surfaces with a brown to grey fungus on the underside.
Fusarium wilt can survive for years in sandy soils, like rootknot nematodes. As the name implies, it can be identified by wilting leaves and a yellow color on the underside of leaflets that spread to the rest of the plant. Crop rotation, avoiding excessive use of nitrogen, and eliminating debris can help with prevention. Other diseases include gummy stem blight, bacterial fruit blotch, rind necrosis, and watermelon mosaic virus.
Storage & Packaging
At 59°F to 60°F watermelon can be stored for about 2 weeks; lower temperatures (below 55°F) may add another week. Chilling injury can occur if temperatures fall below 45°F for any period of time and can cause pitting, flesh discoloration, loss of flavor, and increased decay upon return to room temperature.
In terms of shipping, various packaging options exist, but all should provide adequate cushioning and be thoroughly inspected for cleanliness and structural integrity.
References: Alabama Cooperative Extension, National Watermelon Promotion Board, NC State University Cooperative Extension, Texas A&M AgriLife Extension, University of Florida/IFAS Extension, University of Georgia Cooperative Extension, USDA.
GRADES & GOOD ARRIVAL
Grades are divided into U.S. Fancy, U.S. No. 1, and U.S. No. 2; for all grades, watermelon with good external quality will be mature, well-formed, not overripe, and free from anthracnose, decay, and sunscald. Size and shape, as well as factors such as discoloration and bruising will also affect grades.
Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the percentage of allowable defects, provided: (1) transportation conditions were normal; (2) the USDA or CFIA inspection was timely; and (3) the entire lot was inspected.
|U.S. Grade Standards||Days Since Shipment||% of Defects Allowed||Optimum Transit Temp. (°F)|
There are no good arrival guidelines for this commodity specific to Canada; U.S. guidelines apply to shipments unless otherwise agreed by contract.
References: DRC, PACA, USDA.
• Anthracnose is a free-from defect and always scored against the serious damage tolerance
• If present, anthracnose is scored against the decay tolerance when penetrating the rind or when spots are large and soft enough to give way with finger pressure
• Seedless watermelons with seeds are scored as a defect when they have more than 10 mature seeds (not to include pips or caplets) visible when cut into four equal sections (one lengthwise cut and one crosswise cut)
• Melons, being pale red or lighter in color are scored as ‘immature’ against the 5% tolerance for serious damage.
Source: Tom Yawman, International Produce Training, www.ipt.us.com.