Watermelon Growing Guide

The scientific name of Watermelon is Citrillus lunatus and the plant is an annual fruiting vine that requires a relatively long, hot growing season to produce the iconic summertime treat familiar to picnickers everywhere. Actually Watermelon is one member of the very large Cucurbitaceae family of plants, a group that includes most of the vining vegetables, including squash, cucumbers, and pumpkins. The watermelons that are grown in domestic gardens are all cultivars of the Citrillus lunatus species. Watermelon has been in cultivation for many centuries, thought to have originated almost five thousand years ago in the Kalahari Desert of Africa. The seeds were brought to the United State by enslaved Africans. Thanks to hybridizing, there are over hundred cultivated varieties of watermelons, in assorted sizes, shapes, and colors. 

Furthermore, Watermelon is a sprawling, prostate vining plant with large, lobed leaves with a hairy, coarse texture. The plants bloom with yellow flowers in mid- to late-summer. The deliciously edible fruits with thick rinds grow and ripen quickly for harvest in late summer and early fall. Each of the plant produces 2 to 4 watermelon fruits. 

The Modern watermelon cultivars are categorized into 4 groups:

- The picnic melons are jumbo-sized, fifteen to fifty pounds.

- The Icebox melons are smaller family-sized fruits, five to fifteen pounds.

- The seedless melons are hybrids bred to be self-sterile. They weigh ten to twenty pounds.

- The Yellow/orange-fleshed melons are often considered to be sweeter than red and pink watermelons.

Watermelons are usually planted from seeds sown directly into the garden as soon as the soil warms to about seventy degrees Fahrenheit. In cool regions with short growing seasons, the Watermelon seeds are started indoors 2 to 4 weeks before the last frost date. Most watermelons take eighty to ninety days to mature, although there are short-season varieties that are ready to harvest about seventy days after the seedlings sprout.

Watermelon Plant Info

The botanical name: The botanical name is   Citrillus lunatus.

The common name: The common name is Watermelon.

The plant type: Watermelon is an annual fruiting vine.

The sun exposure: Watermelon plants prefer full sun.

The size: Nine to eighteen inches tall; ten to fifteen foot vine spread.

Soil type: The plant does well in loamy, sandy, well-drained soil.

The soil pH: Slightly acidic to neutral (6.0 to 6.8)

The native area: Watermelon is native to Western Africa.

USDA Hardiness Zones: Grown as an annual in zones two to eleven. 

Watermelon Varieties

There are different varieties of Watermelon.

The early/ short-season varieties mature in seventy to seventy-five days:

- The Blacktail Mountain: The Blacktail Mountain has red flesh with a dark green rind. They weigh six to twelve pounds.

- The 'Faerie': The 'Faerie' produces watermelons with red flesh and a yellow rind. The 'Faerie' are relatively small fruits, at five to six pounds.

- The 'Golden Crown: The 'Golden Crown watermelons have red flesh and yellow rinds. They weigh four to seven pounds.

- The 'Sugar Baby: The 'Sugar Baby is a great red-fleshed cultivar. Melons weigh six to ten pounds.

The long-season varieties mature in eighty to eighty-five days:

- The 'Ali Baba: The 'Ali Baba has oblong-shaped melons with red flesh. Melons weigh twelve to thirty pounds.

- The 'Moon and Stars: The 'Moon and Stars is a hybrid plant with beautiful melons. Both red- and yellow-fleshed cultivars are actually available.

- The 'New Queen: The 'New Queen has orange-fleshed melons with few seeds and high sugar content. The 'New Queen weigh five to six pounds.

The seedless varieties: The so-called seedless varieties of watermelon are not truly seedless, but the seeds are small, white, and edible. These are self-sterile hybrids. The seedless watermelons actually have a lower germination rate and they are more expensive than seeded watermelons, so starting them in peat or paper pots will give you a slight edge over starting them in the ground.

- The 'Revolution: The 'Revolution is a red-fleshed melon that matures in eighty days. Melons are twenty to twenty-six pounds.

- The 'Superseedless: The 'Superseedless has red-fleshed melons that are ready to harvest ninety to ninety-five days after sprouting. Melons are sixteen to twenty pounds.

- The 'Sweet Bite: The 'Sweet Bite has red-fleshed melons that are ready to harvest in about seventy-five days. Melons are five to eight pounds.

- The 'Triple Gold: The 'Triple Gold is a yellow-fleshed melon that matures in about seventy-five days. Fruits way eight to ten pounds. 

How to Plant Watermelons

You can either sown the Watermelons direct in the garden after danger of frost has passed, or you can start them indoors in paper or peat pots, 2 to 4 weeks before your last frost date. Don't rush to plant the watermelons, just wait until air temperatures remain steady at seventy to eighty degrees Fahrenheit, about the time the peonies begin to bloom. The Watermelon seeds need warm soil to germinate. Outdoor soil can be warmed to the necessary seventy degrees Fahrenheit by covering it with black plastic.

Watermelons are usually planted in slightly mounded hills spaced four to six feet apart; Watermelon plants are large plants that need room to sprawl. Plant 4 to 5 watermelon seeds in the center of the hill, about one inch deep. When the watermelon seeds sprout you can thin them out, leaving 2 or 3 plants per hill. If planting from nursery seedlings or seeds started indoors, plant 2 transplants per hill.

In cooler climates, row covers can be used to keep the young Watermelon plants warm. Row covers will also protect the Watermelon plants from the many insect pests that are attracted to watermelons, but they actually need to be taken off when the flowers bloom to ensure pollination.

Light requirement

Watermelons actually require full sunlight in order to thrive. The Watermelon plants can also tolerate some partial shade, mostly in hotter climates, but plenty of sun is required to develop the sugars in the melons. Excessively shady conditions will actually reduce the number and size of the fruits.

Soil requirement

Watermelon plants grow well in almost any well-draining rich soil. A mildly acidic to neutral soil pH of 6.0 to 6.8 is best for growing Watermelons. Heavily amending the soil with plenty of organic matter before planting is advised, as the plants are heavy feeders.

Water requirement

Watermelons actually need regular watering when they are first transplanted. Once the plant begins setting fruits, you can ease up on the water, unless it is an especially dry season. Their roots are relatively deep and they can withstand short dry periods. In fact, the watermelons will lose sweetness if given too much water.

Temperature and humidity requirement

Watermelon plants prefer hot growing conditions, eighty degrees Fahrenheit and higher. Watermelons will do equally well in humid and arid conditions provided the soil moisture is adequate.

Fertilizer requirement

Watermelon plants are actually heavy feeders. Make sure your soil for planting is well amended with organic matter before planting. If your soil is lacking in organic matter you can add a slow-release organic fertilizer at the start of the season. To keep the watermelons growing steadily, you can side dress at mid-season with a layer of compost.

If you choose to apply chemical fertilizer, feed early with a fertilizer that contains more nitrogen than phosphorus and potassium, since this will encourage the growth of the leaves and vine. But after flowering begins, fertilize the plant a second time with a low-nitrogen fertilizer that encourages growth of flowers and fruit.

Growing Watermelon from seed

The Watermelon seeds do not actually require any treatment (eg soaking, stratification) before sowing. The Watermelon seeds actually grow best when they are sown directly into the garden.

- Sow the Watermelon seeds directly in the garden 20mm deep and 60-80cm apart, with rows 150-180cm apart.

- Make sure you keep the soil moist but never wet or dry.

- The watermelon seeds should germinate in around ten to fourteen days at a soil temperature of 27-32°C.

- The young Watermelon seedlings will need protection from pests, pets and weather until they are established.

Watermelon is actually a tender crop that is sensitive to frost. Don’t transplant the Watermelon seedlings or sow the seeds outside until all danger of frost has passed.

How to Harvest Watermelon

Judging the ripeness of a watermelon actually requires some experience, but there are a few signs that can help you learn how to determine when they are ready for harvest:

- The watermelon rind will start to become dull.

- The curly tendrils on the vine, near where the melon attaches, will actually turn brown.

- You will not be able to pierce the rind with your thumbnail.

- The part that rests on the ground will change from pale light green to a pale yellow.

Watermelons are best eaten right away. The cut watermelon should be refrigerated and only keeps for a few days. Do not store the uncut melons in the refrigerator. Opt for a cool room (forty-five to fifty degrees Fahrenheit), if possible. In this environment, uncut melons will keep for up to 2 weeks. 

Pests and disease control

One of the biggest watermelon pests is the cucumber beetle. Monitor for the eggs early. If you are using row covers, you will exclude many of them from the vines. Also Watermelons are prone to aphids, vine borers, and mites.

Some diseases can be a problem to Watermelon plants, which include anthracnose, fusarium wilt, alternaria leaf spot, and gummy stem blight. If these diseases are prevalent, you can choose resistant varieties of watermelon. Watermelon plants can also be prone to powdery mildew, but this is rarely serious, only unsightly. Ground-level watering, rather than overhead watering, will keep soil spores from splashing on the leaves and causing mildew.