FACT SHEET 1-Water Melon growing.pdf - Nabuur

SUSTAINABLE LIVELIHOODS INTERNATIONAL (SLINT)
UGANDA COUNTRY PROGRAMME
SLIN T
FACT SHEET 1 1
WATERMELON GROWING
Introduction
Watermelon (Citrullus lanatus) is one of the most widely cultivated crops in the world. It accounts for
6.8% of the world area devoted to vegetable production. Watermelon originally came from southern
Africa and is now grown in most parts of the world.
Varieties of water melon
Watermelon belongs to the family Cucurbitaceae. There are more than 100 different varieties of
watermelons, available in many sizes, shapes, and colors. The interior flesh may be red, pink, orange or
yellow. There are seedless varieties and super-sweet round ones. The common commercial watermelon
varieties include: ‘sugarbaby’, ‘crimson sweet’, ‘charleston gray’ and ‘yellow crimson’.
Climate and weather
Watermelon prefers a hot, dry climate (daytime temperatures between 22 to 30°C). It can survive desert
conditions when groundwater is available. It grows better in full open sun, with no shade. Watermelon
fruits that are grown under hot and dry conditions have higher sugar content than fruits that those grown
under cool and humid conditions.
Soils
Watermelon requires well-drained, neutral or slightly alkaline soil with pH of 7.0, preferably light sandy
soils. It grows best in sandy or sandy loam soils, although yields on clay soils can be increased
significantly by mulching raised planting rows. Watermelons grown in heavy soils are subject to fruit
cracking.
Fertiliser use
Watermelon can be grown with little or no fertiliser after heavy fertiliser crops have been harvested.
However, nitrogen (N) and magnesium (Mg) deficiency will reduce fruit-set. Calcium deficiencies in
organic soils may also drastically reduce yields. Dolomitic limestone could be applied to offset Mg or
Calcium (Ca) deficiencies. Pre-plant broadcast applications are recommended in preference to bandapplied
pre-plant fertilizer to prevent seedling salt injury. N should be applied in split dressings, at
planting, at branching, just before flowering and after setting of the first fruit, preferably in nitrate form.
Potassium (K) is important in preventing fruit cracking. Application of calcium sulphate may be needed
to lower the pH of alkaline soils. In a light sandy soil apply 10 t/ha of organic manure, 60 kg/ha N, 60
kg/ha P2O5 and 120 kg/ha K2O in the following manner: All organic matter and one-third of the N, P2O5
and K20 broadcast before planting, another third side dressed when the runners start to grow, and the
remainder during the fruit enlargement stage. Peak uptake of nutrients occurs during fruit swelling.
1 A Fact Sheet prepared by SLINT-Uganda in partnership with Butikiro volunteers on Nabuur.
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Soil preparation and planting
Watermelons are deep-rooted, so before seeding, the soil should be deep-ploughed to at least one foot
deep. Watermelon is normally grown from seed by direct seeding in wet warm soil. The planting should
be done immediately after the beginning of the first rains.
Spacing and depth
Watermelon vines require considerable space. Plant seeds one inch (3-5cm) deep holes, spaced 6 feet (1.2
to 2m) apart. Allow 7 to 10 feet (2 to 2.5m) between rows. After the seedlings are established, thin them
and leave the best three plants per hole. Single transplants should be 2 to 3 feet apart and double
transplants 4 to 5 feet apart in the rows.
Watering
Always plant seeds into moist soil. Do not irrigate until after germination or the seeds will rot. The
highest yields and quality are achieved by maintaining the plants free of water stress from establishment
to final harvest.
• Fully wet the soil profile in the plant row at or before planting.
• After planting, allow roots to grow out into the moist soil profile, encouraging a large root system.
During this time, water only when required to stop the plant going into water stress, and then water to
fully rewet the soil profile.
• Avoid frequent short watering.
• After flowering, water when soil approach the refill point and water to field capacity until the end of
harvest.
Care
Watermelons should be kept free from weeds by shallow hoeing and cultivation. The plants have
moderately deep roots and watering is seldom necessary unless the weather turns dry for a prolonged
period.
Extended periods of extremely dry weather when the melons were maturing can cause watermelons to
rotting on the ends. This may be aggravated by continued deep hoeing or close cultivation. Mulching the
plants helps to reduce this problem.
Crop management to improve sugar content
In order to enhance the sugar content of the water melon:
• Plants should be maintained free of water stress from first flower until the end of harvest, including
through the harvest period.
• Root health is critical in producing fruit with high sugars. It is critical to start the crop cycle with a
fully wetted soil profile, then water to field capacity when the soil moisture content falls to a
predetermined refill point.
• Fruit soluble solids can be improved by removing small fruit that will not be harvested about seven
days before the start of harvest
• Plants should be kept supplied with sufficient N, P, K and Ca in balanced applications so that plants
don’t run out of nutrients before harvest.
• Fruit load controls vegetative plant growth.
• High N applications – more than 100 kg/ha N – do not reduce flowering or fruit set.
• Growing locations which provide long sunny days with maximum temperature below 37oC and cool
nights provide the best conditions for sugar accumulation in the fruit.
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• There is significant genetic potential to produce fruit with higher soluble solids than current standard
varieties.
Agronomic performance of various watermelon varieties
Germination rates
Commercial varieties have varying germination rates. ‘Crimson Sweet’ and ‘Charleston Gray’ germinate
in the shortest time frame (6 and 7 days respectively) after sowing, (when soil temperature is in the
optimum range of 21-30oC), while ‘Sugarbaby’ and ‘Yellow Crimson’ germinate after 9 and 11 days.
Other varieties can take even a month.
Flowering
Flowering starts from the sixth week after planting and the first flower to open is always a male flower.
Sugarbaby’ takes about 45 days to flower while ‘Crimson Sweet’, ‘Yellow Crimson’ and ‘Charleston
Grey’ take 55, 58 and 59 days, respectively. The opening of the first female flower occurs about 6-13
days after the opening of the first male flower. On average, watermelon flowers in about 80 days after
planting. Sugarbaby’ takes the shortest time to open the first female flower (51 days), ‘Yellow Crimson’
(66 days), Charleston Gray’ and ‘Crimson Sweet’ (68 days).
Maturity period
The maturity period is highly variable and can take up to 135 days. ‘Sugarbaby’ takes the shortest time to
mature (101 days) followed by ‘Yellow Crimson’ (105 days), ‘Charleston Gray’ (111 days) and ‘Crimson
Sweet’ (113 days). There is a strong correlation between the number of days to maturity and the number
of days to the opening of the first female flower.
Length of the main vine and number of branches
The length of the main vine varies significantly among the different varieties: Crimson Sweet’ has the
shortest main vine (201cm) and is also the least branched (5 branches), followed by ‘Sugarbaby’ (228cm
with 7 branches), ‘Charleston Gray’ (233cm with 7 branches) and ‘Yellow Crimson’ (244cm with 9
branches).
Number of fruits and yield
The number of fruits per plant also varies. ‘Yellow Crimson’ produces an average of 3.45 fruits/plant
(1104 fruits/ha); ‘Sugarbaby’ 2.39 fruits/plant (765 fruits/ha) averaging 2.05 kg in weight while
‘Charleston Gray’ produces an average of 1.5 fruits/plant (480 fruits/ha) averaging 1.77kg in weight.
‘Crimson Sweet’ has the lowest yields of 0.89 fruits/plant (285 fruits/ha) weighing 1.44kg on average.
There is a strong correlation between the number fruit number and the two yield components i.e. main
vine length and branch number.
Generally, ‘Yellow Crimson’ is one of the best commercial varieties with agronomic traits that lead to
high yields. These include long main vine and extensive branching which are highly correlated to yields.
Harvesting
Watermelons take between 100-135 days to mature, depending on the variety. It should be harvested by
hand when the fruits have fully ripened. Many farmers experience difficulty in determining when
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watermelons are ripe. A combination of the following indicators could be used to determine if the
watermelon is ripe for harvesting:
• Light green, curly tendrils on the stem near the point of attachment of the melon usually turn brown
and dry;
• The surface color of the fruit turns dull;
• The skin becomes resistant to penetration by the thumbnail and is rough to the touch; and
• The bottom of the melon (where it lies on the soil) turns from light green to a yellowish color, i.e. as
watermelon ripens, the ground spot changes from pale green or white to cream or yellow.
The ripeness of a watermelon can also be determined by "thumping" the melon with a knuckle. The sound
of a watermelon, when thumped with a finger, is a muffled, dull tone if it is ripe. An immature fruit will
thump with a clear, metallic ringing tone. Many watermelons do not emit the proverbial "dull thud" when
ripe. For these, the dull thud may indicate an over-ripe, mushy melon
Watermelons often weigh between three and 25kgs upon maturity.
Insects and Diseases
Watermelons are susceptible to various pests and diseases that attack the roots, foliage, and fruit resulting
in reduced yields. These include: Fusarium wilt, anthracnose, damping off, gummy stem blight, bacterial
fruit blotch, yellow vine, bacterial rind necrosis, cercospora leaf spot, angular leaf spot, alternaria leaf
spot, Phytophthora blight, powdery mildew, downey mildew and viral diseases. Some cultivars are
resistant to some diseases.
Powdery mildew is one of the severest watermelon diseases. It is caused by 2 fungal pathogens, Erysiphe
cichoracearum and Sphaerotheca fulginea. These fungi occur mainly on leaves, which are most
susceptible 2 to 3 weeks after unfolding. Powdery mildew appears as a dusty white or gray coating/
fungal growth over both upper and lower leaf surfaces or other plant parts, and can be difficult to control.
Exposed vines and fruit are more prone to sunscald, and the vines may shrivel. Powdery mildew also
affects cucumber, squash, pumpkin and other varieties of the family Cucurbitaceae.
Disease control is essential in order to have high-yields and high quality watermelons. For disease
management:
• Select a site with good air circulation and low humidity
• Separate new plantings from old plantings
• Use a crop rotation of at least one year
• Control cucurbit weeds and other weeds.
The most common pests are cucumber beetles. If they attack watermelon plants, apply a suggested
insecticide for control. Watermelon mosaic virus (WMV) and yellow mosaic virus (ZYMV) are other
pests that infect cucurbits: melons, cucumbers, luffas, squash and pumpkins, and are usually transmitted
by insects.
Nutrition
A traditional food plant in Africa, watermelon has potential to improve nutrition and boost food security.
Watermelon contains about six percent sugar by weight, the rest being mostly water (it is 92% water by
weight). As with many other fruits, it is a source of vitamin C but is not a significant source of other
vitamins and minerals unless one eats several kilograms per day. Watermelons also contain a significant
amount of amino acid citrulline.
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