Detailed Explanation of Watermelon Planting Methods and Key Technical Points

Watermelon (scientific name: Citrullus lanatus (Thunb.) Matsum. et Nakai) is an annual trailing vine; the stems and branches are thick and strong, with distinct ridges. The tendrils are relatively thick and strong, with short pubescence; the petioles are thick and densely covered with pubescence; the leaf blades are papery, with a triangular-ovate outline, tinged with white-green, bearing short stiff hairs on both surfaces, and the leaf base is heart-shaped. It is monoecious. Both female and male flowers are borne singly in leaf axils. The male flower pedicels are 3-4 cm long, densely covered with yellow-brown long pubescence; the calyx tube is broadly bell-shaped; the corolla is pale yellow; the stamens are nearly free, the filaments are short, and the anther cells are curved.

The most suitable time to plant watermelon is in mid-to-late February.

Recommended watermelon planting methods:

1. Cultivation season: It can grow normally when the temperature is above 14°C. Using different cultivation techniques, sowing can be done from mid-January to late July in summer, and harvest can be from May to October.

Early spring protected cultivation: Sow and raise seedlings in mid-to-late February, with a seedling age of 35-40 days; use heated seedling raising, transplant into the greenhouse in early-to-mid April, and bring to market in early June. 

Spring open-field cultivation: Sow from late March to late May, with a seedling age of about 30 days. Raise seedlings under protection, and transplant into open fields after the last frost or cover with small arched tunnels. 

Summer delayed protected cultivation: Sow in late July, with a seedling age of about 20 days. Cover with greenhouse film in early September, add insulating straw curtains in early September, and bring to market around October. 

Watermelon cultivation techniques:

1. Site selection

It is advisable to choose sandy loam soil with deep soil layers, loose and fertile texture, and convenient drainage and irrigation, and to cultivate in fields where cucurbit crops have not been planted for within 5 years in dry land and within 3 years in paddy fields.

2. Land preparation and fertilization

Deep plow the watermelon field before winter to freeze the soil clods, and prepare the land in a timely manner before transplanting. The watermelon field should have three ditches supporting each other, so that the field dries after rain, the soil is loose, and the seedbed surface is level. Base fertilizer is mainly high-quality organic fertilizer and cake fertilizer, supplemented by inorganic fertilizer, generally accounting for 60%-70% of the total fertilizer application; nitrogen, phosphorus, and potassium should be reasonably matched, and micro-fertilizers should be applied as base fertilizer or sprayed according to deficiency conditions.

The amount of fertilizer applied depends on soil fertility and cultivated variety. Generally, for medium-fertility fields, combine with land preparation and apply 3000-4000 kg of decomposed organic fertilizer and 60-80 kg of 45% nitro-sulfur-based or potassium sulfate-type controlled-release fertilizer per 667 sq m, and do not apply chlorine-containing fertilizers.

Small-fruit-type watermelons and grafted watermelons can be fertilized 20% less. Use high-ridge planting, with wide ridges 4-4.5 m and narrow ridges 2.0-2.5 m. Wide ridges can be planted on both sides with vines climbing toward each other, or planted in the middle with vines climbing to both sides; narrow ridges are planted on one side with vines climbing in one direction. 

3. Transplanting

Early-maturing watermelons have a seedling age of about 1 month and can be transplanted when 2-3 true leaves have grown. Mid-maturing watermelons can be transplanted at a seedling age of 20-25 days, and late-maturing watermelons at a seedling age of 7-10 days. Wide ridges are planted with 2 rows, and narrow ridges with 1 row. For small-fruit-type watermelons in greenhouse trellis cultivation, plant 1500-1800 plants per 667 sq m; for ground-creeping cultivation, use three-vine or four-vine pruning and plant 600-750 plants per 667 sq m.

Medium and large watermelons are generally planted at 650-700 plants per 667 sq m, and grafted seedless watermelons at 300-400 plants per 667 sq m. Dig transplanting holes according to plant and row spacing, place the nutritional pot into the transplanting hole with the cotyledons oriented in the same direction as the ridge, at a depth level with the ridge surface, fill the seedling hole with fine soil, and water with human and livestock manure and chemicals to settle the roots.

Cover with film while transplanting; the film width should be no less than 80 cm. Film covering should achieve a fine and level seedbed surface, with the film tightly attached to the seedbed surface and sealed firmly all around; broken film areas should be sealed tightly with fine soil.

Generally, three-vine pruning is used. When the main vine has 8-9 leaves, select and retain the main vine and two robust side vines, and remove all other secondary and tertiary vines. Pruning should not be done on rainy days to prevent the spread of diseases. When the vine grows to about 50 cm, combine with pruning and press the vine with soil; thereafter press once more every 3-4 nodes, for a total of 2-3 pressings per vine, and arrange the vines evenly.

Reverse pressing. When watermelon growth is excessively vigorous, use reverse pressing. Dig a pit 7-10 cm deep, push the vine toward the root into the pit, causing the rear vine to arch up, then fill with soil and press firmly; this can control excessive growth and increase fruit setting rate.

Vine clamping. When the 2nd-3rd female flower appears, to help the fruit set firmly and grow large, vine clamping can be used. At a height of one finger above the ground, clamp the vine with two wooden strips about 7 cm long to flatten the vine, ensuring the vascular bundles are not broken, achieving the effect of damaging the skin and flesh but not the bones and tendons.

Stem lifting. To make the young fruit set steadily, forcefully lift the vine behind the young fruit, and when a "crack" sound is heard, "crack at the back, fruit sets at the front."

Head coiling and tip pinching. When watermelon enters the swelling stage, the vine in front of the fruit should be properly suppressed and must not be allowed to grow vigorously, otherwise it will consume nutrients and affect fruit swelling. Head coiling and tip pinching means pulling the vine in front of the fruit back, circling it on one side of the watermelon, and pinching off the vine tip by hand.

4. Fruit setting

The 2nd and 3rd female flowers on the main vine or the 1st and 2nd female flowers on side vines should be selected and retained for fruit setting. To ensure fruit setting at suitable nodes, artificial assisted pollination should be used in low-temperature or rainy weather to help preserve flowers and fruits. After the fruit sets firmly, finely level and pat flat the ground beneath the young fruit and make it slope-shaped, then place the young fruit along the slope and arrange the young fruit and vine in a straight line. After the fruit has fully grown, turn the fruit in a timely manner. When turning, rotate in one direction, about 1/3 each time. 

5. Topdressing

When the young fruit grows to the size of an egg, apply fruit-swelling fertilizer according to plant growth, generally applying 15-20 kg of 45% nitro-sulfur-based or potassium sulfate-type controlled-release fertilizer per 667 sq m. 

6. Water

During the seedling stage, water as little as possible, or even not at all, to promote the formation of a well-developed root system; control water before flowering and fruit setting to prevent excessive growth; after fruit setting, ensure sufficient water supply to facilitate fruit swelling and increase weight. Do not water 7-10 days before harvest, so that the fruit accumulates sugar.

When water is lacking, irrigate in the early morning and at night when temperatures are lower. Use furrow irrigation and seepage into the seedbed, that is, irrigate into the ridge furrow, and once the water has seeped through the melon ridge, immediately drain the remaining water in the furrow. After irrigation and rain, immediately drain accumulated water in the field, otherwise it is easy to cause root and vine rot.

7. Harvest

Harvesting should preferably be done in the morning. For long-distance transport or storage, harvest at about 80% ripeness; for same-day sales in nearby suburbs, harvest at about 90% ripeness, and absolutely avoid selling unripe melons. Generally, early-maturing varieties are harvested about 30 days after pollination, mid-maturing varieties about 35 days, and late-maturing varieties about 40 days.

The speed of fruit ripening is affected by temperature, light intensity, and time. It is best to note the date at pollination, and when maturity is expected, take sample melons, cut open the fruit, measure its sugar content and taste it, and after confirming maturity, harvest in batches according to the markings. 

8. Disease and pest control

The main diseases of watermelon include Fusarium wilt, anthracnose, viral disease, powdery mildew, and Phytophthora blight; the main pests include black cutworm, aphids, red spider mites, Aulacophora femoralis, melon maggots, leafminers, and others. Implement crop rotation of more than 4-5 years, select disease-free seeds, and disinfect seeds by soaking in 100-fold formalin solution for 30 minutes.

Main control methods for fungal diseases: promptly pull out and burn diseased plants when found, and disinfect the diseased holes with lime or 400-fold 50% amobam. In the early stage of disease, 500-1000-fold 50% amobam solution can be poured at the root zone for control. Promote watermelon grafting and root replacement technology. Apply decomposed organic fertilizer and increase phosphorus and potassium fertilizer.

During the watermelon growth period from May to July, alternately use 1000-fold 70% thiophanate-methyl solution, 500-700-fold 25% carbendazim solution, 1000-fold 50% zineb solution, and 1:1:200 Bordeaux mixture every 7-10 days for control.

For black cutworm, melon maggots, and Aulacophora femoralis, early spring plowing and harrowing can be used to eliminate eggs, sugar-vinegar traps can be used to attract and kill moths and eliminate adults, and 800-1000-fold 90% trichlorfon solution can be poured at the roots or mixed with a small amount of water with fresh grass or fried aromatic cake fertilizer for trapping and killing. For red spider mites and leafminers, spray 1000-fold 50% dimethoate solution or 1000-1500-fold 80% dichlorvos solution.