How To Grow And Care For Watermelon

Grow a slice of summer right in your garden. Watermelons are heat-loving plants that love to bask in the Southern sun. While they do require a bit of room, watermelons are easier to grow than you might think. And they are immensely rewarding. Each plant produces two to four sweet, juicy fruits each weighing between six and fifty pounds, depending on the variety. Be the star of your next barbeque—learn how to grow and care for watermelon, then share the bounty with family and friends.

Plant Attributes

Common Name	Watermelon
Botanical Name	Citrullus lanatus
Family	Cucurbitaceae
Plant Type	Annual, Vine
Mature Size	16 to 24 in. tall, 48 to 96 in. wide
Sun Exposure	Full Sun
Soil Type	Moist but Well-Drained
Soil pH	Slightly Acidic to Neutral (6.0 and 7.5)
Bloom Time	Summer
Flower Color	Yellow
Hardiness Zones	Not Winter Hardy
Native Area	Africa
Toxicity	Non-toxic

Watermelon Care

Watermelons need plenty of sunshine, space, and water to grow. Plants grow as long vines, with curly tendrils and large, lobed leaves. The vines of full-sized varieties can reach lengths of six feet, though compact varieties and bush-type watermelons are available for smaller spaces. Bees are your friend in the melon patch. Watermelon plants produce separate male and female flowers, and require pollination by honeybees, native bees, and other pollinators. 

Light

For best flowering and fruit production, plant watermelon in a location receiving 8 to 10 hours of sunlight per day. 

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. 

Water

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. 

Temperature And Humidity

Watermelons grow best when daytime temperatures are between 70 and 85˚ F, though plants tolerate temperatures up to 90˚ F. 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.

Fertilizer 

Incorporate a complete fertilizer, such as 10-10-10, into the soil before planting time at the rate of 3 pounds per 100 square feet of garden. Once the watermelon plant is established, but before the vines begin to run, side dress plants with a nitrogen fertilizer, such as 34-0-0, using 1 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.

Types of Watermelon

When selecting watermelon varieties for the garden, your first consideration is how much space you have available to grow the crop. Many watermelon varieties require up to 18 to 24 square feet per plant. That’s a lot of garden real estate. For gardeners with space limitations, there are plenty of options including smaller "icebox" varieties and bush-type melons. Seed-formation is another consideration in selecting melons. Many seedless varieties are available, though you won’t be able to host the annual watermelon seed-spitting contest. It is also a good idea to select disease resistant varieties. Finally, if you are interested in producing a fast crop, you might look for an early producing variety.

Standard Varieties

These watermelon varieties produce large fruits on long vines. Most are seeded and many have been bred for disease resistance against fusarium, anthracnose, and other common ailments. Cultivars include 'Charleston Grey', 'Crimson Sweet', 'Jubilee', 'Sangria', 'Moon & Stars', and 'Royal Sweet'.

Icebox Varieties

Icebox is a catch-all term for medium sized watermelons produced on shorter vines. Most varieties produce melons weighing eight to ten pounds. These small fruits do not sacrifice flavor—they are juicy and incredibly sweet. Though they didn’t gain popularity until the 1990’s, icebox melons include many heirloom varieties. Some favorites include 'Sugar Baby', 'Sweet Beauty', 'Mickeylee', and 'Yellow Doll'.

Seedless Varieties

As their name suggests, seedless watermelons do not produce the brown or black seeds found in standard watermelons. They do often have rudimentary seed structures, but these are small, soft, and tasteless, and can be eaten along with the melon. Seedless varieties are all hybrids, meaning you cannot save seeds to grow plants the following season, as the seedlings will not be true to type. Good varieties for Southern gardens include: 'Supersweet', 'Genesis', 'King of Hearts', 'Majestic', and 'Cotton Candy'.

Bush Varieties

Taking up the least space in the garden, bush verities produce medium sized fruits on compact, bushy vines that can also be grown in containers. These smaller plants typically produce fewer fruits, around 2-3 per plant depending on variety. Try 'Bush Charleston Gray', 'Bush Jubilee' or 'Cal Sweet Bush'.

Early Varieties

This grouping includes some of the fastest ripening varieties for an early crop. Most are icebox plants, producing medium sized fruits: 'Bush Sugar Baby', 'Golden Crown', 'Sugar Baby', 'Yellow Baby', and 'Early Crimson Treat'. 

How To Grow Watermelon 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 to 65°F at a depth of 4 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.

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 required spacing, use the common spacing for standard vines, spacing plants 36-48 inches apart, in rows 6 to 8 feet apart.

How To Start Watermelon Seeds:

1. Prepare the planting bed, incorporating fertilizer as described above.
2. Create small hills of soil about 6 to 8 inches high and 18-24 inches wide, spacing these according to variety recommendations. 
3. Sow 4 to 5 seeds per hill at a depth of 1 inch.
4. Water hills well and maintain even moisture during germination.
5. 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. 
6. Mulch plants with dry, weed-free grass clippings, straw, cottonseed hulls, or wood chips to control weeds and conserve soil moisture.

How To Grow Watermelon from Transplant

Alternatively, you can purchase young watermelons 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.

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 8 to 10 gallons of soil per plant. Make sure the container has good drainage holes and be prepared to water and feed plants regularly.

How Long Does It Take for a Watermelon To Grow

Watermelons are not a quick crop. Plants require between 65 and 100 days from the time of planting until the fruit is ripe, depending on variety. Smaller melon varieties often mature more quickly, but this is not always true. When selecting varieties, look for information on seed packets and in catalogs regarding maturation time. This is typically listed as “days to maturity” or simply written as a number followed by the word “days,” such as 75 days or 80-90 days.

If you are looking for a quicker-maturing melon, select a variety with the fewest days to maturity, many of which include the word “early’ in their name. You might also consider purchasing transplants rather than starting from seed, which cuts about 2 weeks off the time to maturity, as the plants are already up and growing. 

You can use approximate maturity times to help plan for an extended harvest. If you have the space available, you might consider planting an early-ripening variety as well as one that takes longer to mature. With this strategy, you can have melons ripening from mid- to late summer.

Harvesting Watermelon

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 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.

Common Problems, Pests, & Plant 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 infecting 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. 

If you have extra room in the garden, give watermelons a try. They are a fun crop to grow and a delight to eat!