Watermelon (Citrullus lanatus)

Watermelon (Citrullus lanatus) is a flowering plant with a vine-like appearance native to Western Africa. Watermelon bears fruit that are widely cultivated and consumed across the world. Watermelons grow in tropical and temperate climates and require warmth to grow. There are 1000 varieties around the world.

I. Appearance and Characteristics

Watermelon (Citrullus lanatus) is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 varieties.

The watermelon is an annual that has a prostrate or climbing habit. Stems are up to 3 metres (10 feet) long and new growth has yellow or brown hairs. Leaves are 60 to 200 millimetres (2+1⁄4 to 7+3⁄4 inches) long and 40 to 150 mm (1+1⁄2 to 6 in) wide. These usually have three lobes that are lobed or doubly lobed. Young growth is densely woolly with yellowish-brown hairs which disappear as the plant ages. Like all but one species in the genus Citrullus, watermelon has branching tendrils.

Plants have unisexual male or female flowers that are white or yellow and borne on 40-millimetre-long (1+1⁄2 in) hairy stalks. Each flower grows singly in the leaf axils, and the species’ sexual system, with male and female flowers produced on each plant, is monoecious. The male flowers predominate at the beginning of the season; the female flowers, which develop later, have inferior ovaries. The styles are united into a single column.

Watermelon (Citrullus lanatus)
Citrullus lanatus (Thunb.) Cucurbitaceae (7174523558) Len Worthington CC BY-SA 2.0

The large fruit is a kind of modified berry called a pepo with a thick rind (exocarp) and fleshy center (mesocarp and endocarp). Wild plants have fruits up to 20 cm (8 in) in diameter, while cultivated varieties may exceed 60 cm (24 in). The rind of the fruit is mid- to dark green and usually mottled or striped, and the flesh, containing numerous pips spread throughout the inside, can be red or pink (most commonly), orange, yellow, green or white.

A bitter watermelon, C. amarus, has become naturalized in semiarid regions of several continents, and is designated as a “pest plant” in parts of Western Australia where they are called “pig melon”.

Watermelons are plants grown from tropical to temperate climates, needing temperatures higher than about 25 °C (77 °F) to thrive. On a garden scale, seeds are usually sown in pots under cover and transplanted into the ground. Ideal conditions are a well-drained sandy loam with a pH between 5.7 and 7.2.

II. How to Grow and Care

Sunlight

For best flowering and fruit production, plant watermelon in a location receiving eight to ten hours of sunlight per day.

Temperature And Humidity

Watermelons grow best when daytime temperatures are between 70ºF and 85ºF, though plants tolerate temperatures up to 90ºF. Plants do not tolerate frost. Wait to plant until after all danger of frost has passed. While watermelon plants are generally tolerant of humidity, diseases can thrive under wet and humid conditions. Watering through drip irrigation or in the morning can help minimize this problem.

Watering

Watermelon (Citrullus lanatus)
Starr 080610-8346 Citrullus lanatus Forest & Kim Starr CC BY 3.0

This plant is not called watermelon for nothing! The large, fleshy fruits are 92% water. As you can imagine, it takes a lot of water to grow a good melon. However, watermelon plants have shallow roots. Plants require about an inch of water per week, but because the roots are in the upper 12 inches of soil, it is best to split this irrigation into two or more waterings during the week, depending on soil type.

Soil

Watermelon plants require warm soil to thrive. Plants tolerate a variety of soils, as long as they are well drained. Loamy and sandy loams are the ideal soil type.

Fertilizing

Incorporate a complete fertilizer, such as 10-10-10, into the soil before planting time at the rate of three pounds per 100 square feet of garden. Once the watermelon plant is established, before the vines begin to run, side dress plants with nitrogen fertilizer, such as 34-0-0, using one pound per 100 linear feet of row. Repeat this application after the plants bloom and fruit are beginning to develop. Don’t be overly generous with fertilizer, as too much nitrogen can encourage excess vine growth at the expense of fruit production.

How To Grow from Seed

Watermelons are easy to grow from seed, however, melon seeds will not germinate well in cold soils. Wait to plant watermelon seeds until the soil has warmed to 60°F to 65°F at a depth of four inches. Watermelon seeds (as well as closely related cucumber and squash) are commonly planted on small mounds or hills of soil to help warm the soil. Hilling hastens germination and promotes faster growth, as well as improving soil drainage.

Watermelon (Citrullus lanatus)
File:Starr-091108-9407-Citrullus lanatus-fruit-Olinda-Maui (24871285402).jpg Forest and Kim Starr CC BY 3.0

If you are planning to grow a seedless variety, it is best to start with small plants, as described in the next section. Refer to your seed packet for plant/hill spacing, as different varieties require more space to grow than others. If you are uncertain about the required spacing, use the common spacing for standard vines, spacing plants 36-48 inches apart, in rows six to eight feet apart.

How to start ưatermelon seeds:

  • Prepare the planting bed, incorporating fertilizer as described above.
  • Create small hills of soil about six to eight inches high and 18-24 inches wide, spacing these according to variety recommendations.
  • Sow four to five seeds per hill at a depth of one inch.
  • Water hills well and maintain even moisture during germination.
  • A week after seedlings emerge, thin the seedlings to two per hill, leaving the strongest plants and cutting the others out with scissors or flower snips.
  • Mulch plants with dry, weed-free grass clippings, straw, cottonseed hulls, or wood chips to control weeds and conserve soil moisture.

Transplanting

Alternatively, you can purchase young watermelon plants from garden centers for transplanting into your garden. When growing seedless varieties, it is best to start with purchased plants, as the seeds are expensive and slow to germinate. One advantage of growing from transplants is an earlier harvest date, as fruits typically ripen up to two weeks earlier when plants are grown from transplants versus seed.

Watermelon (Citrullus lanatus)
Citrullus lanatus (Thunb.) Matsum. & Nakai, 1916 Tenesse85 Public Domain Mark 1.0

Use the same spacing as described for seeds, setting two strong transplants on each hill at the recommended spacing. Handle seedlings carefully as watermelons have sensitive roots. To minimize stress to young plants and root systems, look for seedlings grown in peat pots which can be torn from the root ball. Water plants thoroughly and irrigate regularly to a depth of six inches, ideally through a drip system.

Watermelons can also be grown in containers from either seed or transplant. Compact, bush-type varieties are best for container production. Choose a large container, one that holds at least eight to 10 gallons of soil per plant. Make sure the container has good drainage holes and be prepared to water and feed plants regularly.

Pests and Diseases

As with any crop, growing watermelons is not without its challenges. Poor pollination can cause misshaped fruits. Because watermelons rely on insect pollination, you can encourage bees and other pollinators by planting nectar-rich flowers adjacent to watermelon plantings. Another reason for poor fruit set might be excess fertilization or insufficient plant spacing.

Watermelon plants are susceptible to a variety of diseases including anthracnose, fusarium wilt, gummy stem blight (also called black rot), and bacterial wilt. Purchase seeds from a reputable company and look for disease-resistant varieties when practical. When purchasing transplants, look for signs of infection including dead areas on the leaf edges, and oozing, soggy, or water-soaked regions on the stem.

Most disease organisms can be managed by rotating crops in the garden. Plant melons, cucumbers, squash, and other related crops in a different portion of the garden each year, avoiding the same location for at least three years. Overhead watering can also encourage disease development. Use drip irrigation whenever possible or water plants early in the day to allow the sun to dry foliage. Minimize problems with blossom end rot by keeping the soil uniformly moist, but not saturated. Do not allow the soil to completely dry between watering.

Insect problems include striped and spotted cucumber beetles, squash bugs, and aphids. Managing insect problems is most critical during the seedling and early growth stages. You can use a row cover to exclude these pests from the crop, but you must remove the row cover when plants begin to flower to allow pollinators access to the blooms.

III. Uses and Benefits

  • Culinary uses

Watermelon is a sweet, commonly consumed fruit of summer, usually as fresh slices, diced in mixed fruit salads, or as juice. Watermelon juice can be blended with other fruit juices or made into wine.

The seeds have a nutty flavor and can be dried and roasted, or ground into flour. Watermelon rinds may be eaten, but their unappealing flavor may be overcome by pickling, sometimes eaten as a vegetable, stir-fried or stewed.

Citrullis lanatus, a variety of caffe, grows wild in the Kalahari Desert, where it is known as tsamma. The fruits are used by the San people and wild animals for both water and nourishment, allowing survival on a diet of stammer for six weeks.

Watermelon (Citrullus lanatus)
File:Tsamma Melon (Citrullus lanatus) (6856810070).jpg Bernard DUPONT from FRANCE CC BY-SA 2.0
  • Symbolic uses

The watermelon is used variously as a symbol of Palestinian resistance, the Kherson region in Ukraine, and Eco-socialism. It has also been used as a racist stereotype in the United States.

IV. Harvesting and Storage

Determining when to harvest a watermelon can be a bit tricky. Watermelons do not ripen off the vine once they have been harvested, so it is important to wait for them to be fully ripe before picking. For many varieties, the rind of the melon changes colors as it matures, but this is not a reliable indicator for all varieties. Likewise, the portion of the melon touching the ground often changes color from creamy white to yellow, but again, this will vary with the cultivar.

One of the more reliable indicators of ripeness can be found by looking at the tendril (the curling bit of vine) at the base of the leaf closest to the fruit. When the melon is ready to harvest, the tendril will turn dry and brown. Other cues to look for include a dusty coating that gives the skin a dull appearance. You might also find that the rind becomes hard to pierce with your fingernail and the blossom end of the fruit plumps up. These indicators are not much to go on, but they are a start. The only true way to know if your melon is ripe is to cut it open. Experience will help you determine the best time to harvest different varieties.

Find Where to Buy the Best Watermelon (Citrullus lanatus)

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