Watermelon (Citrullus lanatus) is an iconic summer treat. Watermelon seed-spitting contests are a fond memory for past generations, but perhaps a foreign concept for those who have grown up on the seedless varieties most commonly found in grocery stores today.
Florida has a great climate for growing watermelon, and is actually a leading producer for the nation. While it's generally considered a summer fruit, growers in Florida are lucky enough to be able to plant watermelon for harvest in the winter as well. In fact, Florida is the only state in the country that produces watermelon from December to April.
Watermelon is in the cucurbit family along with other melons like cantaloupe and honeydew. Winter and summer squashes, gourds, pumpkins, and of course cucumbers are also members of the cucurbit family. Originating in Africa, watermelon cultivation has a long history across the globe and even in the Americas. China has been cultivating watermelon since the tenth century and Native Americans were growing watermelon before French settlers even arrived.
Watermelon is an annual vine with curly tendrils and lobed leaves; both the vine and its leaves are "hairy." It has pale yellow flowers. The fruit is a round or oval watermelon with a firm, smooth rind that's typically green with darker marks or stripes. Depending on the cultivar, the fruit can range anywhere between 6 to 50 pounds, and in some rare instances, as much as 200 pounds. Each melon has sweet, juicy pulp that is red, pink, or even yellow. Seeds, if they exist, are black or brown; seedless varieties are also available. (You can read "How Do They Make Seedless Watermelon?" below for a detailed explanation.)
Growing watermelon takes a considerable amount of growing area — in excess of 18 to 24 square feet per plant. Some home gardeners may be intimidated when it comes to growing these large melons. Luckily, there are smaller "icebox" varieties that can be great for gardeners with limited space. Plus, the smaller fruits are easier to harvest and store (thus the name — you can fit them in your icebox, better known today as a refrigerator). If you do want to grow large watermelon varieties, keep in mind that you may find yourself with multiple 15–20 pound watermelons to eat, store, or give away.
If you're looking for something a little different, consider the heirloom variety 'Moon & Stars'. This is not your typical-looking watermelon; 'Moon & Stars' produces dark green melons that have small and large yellow dots that resemble a glowing moon surrounded by twinkling stars. This is a large variety, so be sure you have a location with lots of space for your plant to stretch and grow.
Planting and Care
When planting watermelon you can either plant seeds or transplants; just be careful with transplants as watermelons have sensitive roots. Look for transplants grown in peat pots that can be planted straight into the ground; this can help prevent stress to the young roots.
Plant your watermelons in a location where they will receive full sun. Watermelon is pretty versatile; it will grow in almost any type of soil as long as it's well-drained. Your seed package should have the exact spacing needs for your particular variety. If you aren't sure how far apart to plant your seeds, a good rule of thumb is that plants should be 36 inches apart, in rows 7 to 8 feet apart.
Watermelon plants grow best when temperatures during the day are between 70 and 85 degrees Fahrenheit, although they can handle daytime temperatures up to 90 degrees. With this in mind, the best time to plant watermelon will depend on where you are in the state. Those in North Florida can plant watermelon in March and April and again in July and August. Gardeners in Central and South Florida can plant earlier in the year, where warmer springtime temperatures make planting ideal from January through March. In Central Florida, watermelons can be planted again in August, and in August and September for those in South Florida.
There are a few varieties of watermelon that do particularly well in Florida. If you are planning to grow the popular smaller, icebox-sized watermelons, look for 'Sugar Baby' or 'Mickeylee' varieties. If you have the space and desire to grow larger watermelons look for 'Jubilee' (Florida Giant), 'Crimson Sweet', or 'Charleston Grey 133'.
To get the best-tasting watermelon, avoid stress to your plants from insects, disease, weeds, poor nutrition, or too much or too little water. Watermelons take 80 to 100 days to mature depending on the variety. It can be difficult to know when your watermelon is ready to harvest. Look for the bottom of the melon to be cream-colored or bright yellow; a white or pale green spot means the melon is not yet ripe. Also, check the curled tendril closest to the melon on the vine. When it turns brown and shrivels, the melon should be ripe. Once harvested, watermelons can last a little over a week when kept at room temperature or about two weeks when refrigerated.
Pests and Diseases
Watermelons are not without their vulnerabilities. Gummy stem blight (GSB), also called black rot, is a major disease of watermelon and many other cucurbits. GSB is a fungal pathogen that can lead to little or no edible fruits being produced. The best way avoid GSB is to purchase seeds from a reputable company with a good history of GSB-free seed production. If you're starting with transplants look for these characteristic GSB symptoms: necrotic areas on the leaf margins, water-soaked regions on the stem, and/or gummy ooze coming from the stem. Keeping the debris from any other cucurbit crops you might be growing away from your watermelons is another important precaution to take.
Crop rotation is always a good idea when growing edible plants. When planting watermelons, use an area where watermelons or other cucurbits have not been planted within the last two or three years. Be careful not to wound your fruits when they are being harvested and store them at 45-50 degrees to prevent postharvest black rot.
The use of fungicides may be necessary in some areas, and for some a preventative fungicide spray can be used to help avoid problems from GSB. In addition to GSB, powdery mildew and downy mildew can also cause problems for gardeners growing watermelons and other cucurbits.
If you have the room, watermelon can be a great treat to grow in your yard. For more information on growing watermelon or managing insects and diseases in your home garden contact your county Extension office.
Also on Gardening Solutions
More from UF/IFAS Publications
- Florida Plant ID: Watermelon
- Growing Seedless Watermelons (archived)
- Watermelon, Seedless Citrullus lanatus (Thunb.) Mansf.
Sidebar: How Do They Make Seedless Watermelon?
The average watermelon plant you can grow in your garden is diploid, meaning it has a complete set of chromosomes (2N). To create a seedless watermelon, a diploid watermelon plant is treated with colchicine (a plant-derived chemical) to produce a tetraploid watermelon plant that has double the normal number of chromosomes (4N). This tetraploid (4N) plant is then crossed with yet another diploid (2N) plant, which in turn produces a seed that will become a triploid (3N) watermelon plant. This triploid (3N) watermelon plant is sterile, meaning it cannot produce complete seeds. This is why you sometimes find little white "seeds" in a seedless watermelon; the "seed" is just a seed coat.