A detailed guide to watermelon cultivation methods, teaching you step by step how to grow watermelons well
Watermelon is a major heat-relieving fruit in summer. Its flesh is crisp and tender, sweet and juicy, and rich in mineral salts and various vitamins. It is the largest-selling fruit in China in summer and autumn. To improve yield and quality, let's take a look together with the editor at the current cultivation techniques for watermelon.
Morphological characteristics of watermelon
1. Roots. The roots of watermelon are a deep root system. The main root reaches more than 1 m deep, and lateral roots can extend horizontally 4-6 m. The main root mass is distributed within the 10-40 cm soil layer, with strong ability to absorb fertilizer and water. The regeneration ability of the roots is weak, and they are not easy to recover after injury. In production, direct sowing is often used. If raising seedlings for transplanting, be sure to pay attention to protecting the roots.
2. Stems and leaves. The watermelon stem is also called a vine. The main vine grows upright before 5-6 leaves. When it continues to grow beyond 30 cm and reaches a certain length, because the mechanical tissue is not well developed and cannot support its own weight, it grows prostrate on the ground. The branching ability of the stem is very strong, and it can sprout 3-4 levels of lateral branches, but the lateral branches emerging from the leaf axils of the 3rd-5th leaves on the main vine are relatively robust. Adventitious roots are very easily produced at the stem nodes of watermelon. The method of pressing vines can promote the formation of adventitious roots, increase the absorption area, fix the plant, and prevent the vines from rolling. Leaves are alternate, with types such as deeply lobed, shallowly lobed, and entire.
3. Flowers, fruits, and seeds. Watermelon flowers are small and yellow, monoecious with unisexual flowers, and borne singly in leaf axils. Early-maturing varieties bear the first female flower at the 6th and 7th nodes of the main vine, while mid- and late-maturing varieties produce the first female flower after the 10th node. The interval between female flowers is 7-9 nodes. A small number of bisexual flowers may appear during peak flowering. Flowers open in the early morning and close in the afternoon.
The fruit is oval or spherical, and the color may be dark green, light green, or with dark green stripes or markings. The flesh may be red, yellow, white, etc. Seeds may be black, white, or red, etc. Watermelons can also be divided by seed size into large-seeded watermelons, small-seeded watermelons, and seedless watermelons. The 1000-seed weight is 100 g-150 g for the large-seed type, 40 g-60 g for the medium-seed type, and 20 g-25 g for the small-seed type.
Growth cycle of watermelon
The whole growth period can be divided into four stages: germination stage, seedling stage, vine-running stage, and fruiting stage.
1. Germination stage. From seed swelling to cotyledon unfolding and true leaf emergence is the germination stage. After the seedlings emerge, excessive vegetative growth should be prevented to promote the development of roots and leaves.
2. Seedling stage. From the emergence of true leaves to 5-6 leaves is the seedling stage. Growth during this period is small. In cultivation, good conditions should be provided to promote root development and organ differentiation of the seedlings.
3. Vine-running stage. From the beginning of vine running at 5-6 leaves to the opening of the female flower at the fruit-setting node is the vine-running stage. During this period, the growth rate is fast and the growth amount is large. In cultivation, stem and leaf growth should be promoted to form a certain vegetative system, while excessive growth should be controlled to ensure the formation of floral organs.
4. Fruiting stage. From the opening of the female flower at the fruit-setting node to the beginning of vigorous fruit growth. It can further be divided into 3 periods: fruit-setting period, vigorous fruit growth period, and flesh-transformation period.
Fruit-setting period: from the opening of the female flower at the fruit-setting node to the beginning of vigorous fruit growth. Photosynthates begin to be transported into the fruit. In cultivation, the main task is to regulate the balance between vegetative growth and fruit development to ensure fruit setting.
Vigorous fruit growth period: from rapid fruit growth to the point when fruit size is basically fixed. During this period, fruit growth is large and nutrient uptake is greatest, and it is the key period for yield formation. In cultivation, heavy fertilizer and heavy water should be applied to promote rapid fruit growth.
Flesh-transformation period: from when fruit size is basically fixed to the ripening stage. During this period, sugars transform rapidly, and the appearance takes on the inherent color of the variety. In cultivation, premature senescence of stems and leaves should be prevented to ensure yield and quality.
Environmental requirements for growing watermelon
1. Temperature. Watermelon likes a warm, dry climate and is not cold-tolerant. The optimum temperature for growth and development is 24-30 degrees, the optimum temperature for root growth and development is 30-32 degrees, and the minimum temperature for root hair formation is 14 degrees. During growth and development, watermelon needs a relatively large day-night temperature difference. A relatively large day-night temperature difference can produce high-quality watermelons.
2. Water. Watermelon is drought-tolerant and not moisture-tolerant. When there are many rainy days, humidity is too high, it is susceptible to disease, yield is low, and quality is poor.
3. Light. Watermelon likes light. Under conditions of sufficient sunlight, yield is high and quality is good.
4. Nutrients. Watermelon has a long growth period and high yield, so it requires large amounts of nutrients. For every 100 kg of watermelon produced, about 0.19 kg of nitrogen, 0.092 kg of phosphorus, and 0.136 kg of potassium are absorbed. However, there are obvious differences in nutrient uptake among different growth stages: 0.01% in the germination stage, 0.54% in the seedling stage, 14.6% in the vine-running stage, and the fruiting stage is the period of most vigorous nutrient uptake by watermelon, accounting for 84.8% of the total nutrient amount. Therefore, as the plant grows, the fertilizer requirement of watermelon gradually increases, reaching its maximum when the fruit grows vigorously.
5. Soil. Watermelon has strong adaptability, and sandy soil with loose texture, deep soil layer, and good drainage is best. It prefers weakly acidic soil, pH 5-7.
Cultivation techniques for watermelon
1. Suitable sowing time
Open-field watermelon cultivation is cultivation without protective equipment. Generally, the suitable time for open-field sowing is when the local final frost has passed and the soil temperature is stable at about 15°C. The best sowing time should also be determined according to conditions such as variety, cultivation season, cultivation method, and consumption season. Generally, sowing and seedling raising are done in mid- to late March, planting in mid- to late April, and harvesting for market begins in late June; autumn watermelons are sown in early to mid-July, and harvesting for market begins in late September.
2. Land preparation and applying sufficient base fertilizer
To cultivate watermelon, choose a plot with loose soil, deep soil layer, fertile soil, good drainage, sufficient sunlight, and facing west sun exposure; watermelon land should not be continuously cropped, and generally requires a 4-5 year rotation. Otherwise, Fusarium wilt is severe; the best preceding crop is gramineous crops such as rice and corn, followed by vegetable crops such as potato and Chinese cabbage, but if the preceding crop is cucurbit vegetables, watermelon diseases are severe, so it should not be chosen.
The melon field must be deeply plowed, preferably turned in winter. In deeply plowed land or land with a deep plowing foundation, open drainage ditches around the perimeter, and according to the cultivation row spacing of 2.4-3.0 m including the ditch (ditch width 0.5 m), make beds, open a ditch on one side of the bed surface and apply base fertilizer. Apply 2500-3000 kg of farmyard manure per mu, plus 15-20 kg of phosphate fertilizer, 20-25 kg of 45% compound fertilizer, 2 kg of borax, and 1 kg of zinc fertilizer. To prevent underground pests, a small amount of crystalline trichlorfon may be mixed into the base fertilizer. Cover the base fertilizer ditch well, form melon ridges, and finally cover with plastic film, waiting for sowing or transplanting. When making beds, note that the bed rows should be perpendicular to the spring and summer wind direction. Open the ditch and apply base fertilizer on the bed surface on the side where the wind blows in first, so that after planting the vines align with the wind direction.
3. Seed soaking and germination promotion
1. Seed soaking. Before soaking, sun-dry the seeds for 1 day. Soak the sun-dried seeds in warm water that is not hot to the touch (about 30°C) for 6-8 hours, then remove them, wrap them in a towel or coarse cloth, and rub off the mucilage on the seed coat. To prevent Fusarium wilt, soak again in a 1000-fold solution of thiophanate-methyl for 4 hours. Generally, the soaking time should reach 12 hours. Once the seed coat softens, remove the seeds, rinse them clean with water, and set them aside for germination.
2. Germination promotion. Place the soaked seeds flat on a wet towel, cover the seeds with another layer of wet towel, and place them in a 30-35 degree environment to promote germination. They basically all sprout within 72 hours. When 85-90% have sprouted and shown white, they can be sown.
4. Sowing or transplanting
1. Direct sowing after germination promotion. On the melon ridge near where the base fertilizer was applied, open a shallow ditch or hole 8 cm-10 cm deep, with a plant spacing of 45-50 cm. Sow 1-2 germinated seeds per hole, (after watering thoroughly once in dry conditions) cover with 2 cm-3 cm of soil. With direct sowing after germination promotion, seedlings can emerge after 2-3 days; generally 150 g-200 g of seed is used per mu.
2. Seedling raising and transplanting. The seedling age is 30-35 days. Transplanting begins when the melon seedlings have 3 leaves and 1 heart. The plant spacing is 45-50 cm, and about 450-500 plants are planted per mu. After transplanting, water to settle the roots.
5. Field management
1. Cultivation and drainage. Cultivation begins after all seedlings emerge from sowing or after transplanted plants have recovered. Generally, thinning, loosening soil, and hilling are carried out in combination. During the seedling stage, watering should be minimal, and attention should be paid to "hardening the seedlings" to favor root growth; when the vines are 30 cm long, apply one heavy fertilizer and then hill the soil. Watermelon fruits are large, yields are high, and water demand is great. In dryland cultivation, attention should be paid to irrigation, while in paddy field cultivation, drainage work is especially important. Emphasize that the bed ditches and the drainage ditches around the field should all be connected, with no standing water in the field after rain. This is the foundation for ensuring high and stable watermelon yields. Stop irrigation 6-8 days before fruit ripening to promote sugar transformation and increase sweetness.
2. Topdressing. The basic principles of topdressing in melon fields are: apply seedling fertilizer lightly, first promote then control, skillfully apply vine-extension fertilizer, and heavily apply fruit-swelling fertilizer after young fruits are set.
① Seedling-promoting fertilizer. Seedling-promoting fertilizer is generally applied within one week after transplanting melon seedlings or at the 4-5 leaf stage for directly sown seedlings. When base fertilizer is insufficient or its effect has not yet appeared, apply a small amount of quick-acting fertilizer. Generally, apply 8-10 g of urea (or 20 g of ammonium sulfate) per plant, open a ditch, apply fertilizer, and then cover with soil.
② Vine-promoting fertilizer. This can be done before and after vine extension. Generally, when melon seedlings grow to 40-60 cm, apply 10-12 kg of urea, 8 kg of calcium superphosphate, and 13 kg of potassium sulfate per mu, or use 18-22 kg of 45% potassium sulfate-type ternary compound fertilizer per mu. Apply in a ditch 25-30 cm from the melon roots or between two plants, with a ditch depth of 10-15 cm. After application, cover with soil and water to promote fertilizer absorption.
③ Fruit-swelling fertilizer. The fruit-swelling period is the time of greatest fertilizer demand in the life of watermelon. When the watermelon is the size of an egg, the root system spreads throughout the whole bed. Many melon growers apply fruit-swelling fertilizer in holes at this time. Because hole application concentrates the fertilizer too much, it can burn the roots around the application point, and at the same time it is not conducive to the rapid decomposition and transformation of the fertilizer, which is very different from the fertilizer requirements of the watermelon fruit-swelling period for heavy fertilizer, heavy water, and quick-acting, comprehensive nutrients. Therefore, fruit-swelling fertilizer is best applied as human and livestock manure water plus dissolved chemical fertilizer. When the watermelon is the size of an egg, apply manure water plus compound fertilizer and urea in a ring about 30-45 cm from the base of the melon plant (focusing on the side where the vines extend). For melon growers without manure water, dissolve 8 kg of compound fertilizer, 4.5 kg of urea, and 5 kg of potassium sulfate per mu and apply with water. The concentration of fruit-swelling fertilizer should be light, using water to regulate fertilizer, so that the fertilizer quickly takes effect in a short time. Especially when the soil is relatively dry, a immediate fruit-swelling effect can be obtained. In the later period, foliar spraying is carried out using a 0.4% potassium dihydrogen phosphate solution once every 7-10 days, for a total of 2-3 sprays.
3. Pruning. Watermelon vines and leaves are luxuriant. If allowed to grow freely, the vines overlap each other, which not only affects dense planting but also delays fruit setting. Watermelon pruning methods generally include single-vine, double-vine, and three-vine pruning. Single-vine pruning leaves only one vine per plant. All other lateral vines are removed. The method is simple, and the number of plants per unit area is large and fruit set is high, but the leaves per plant are few, the fruit is not easy to grow large, and both yield and quality are relatively low. Double-vine or three-vine pruning generally retains the main vine and, when the main vine grows to more than 30 cm, double-vine pruning selects and retains one robust lateral vine at the base, while three-vine pruning retains two robust lateral vines as secondary vines or reserve vines, and all other lateral vines are removed; in production, double-vine pruning is mostly used. When pruning watermelon, note first that pruning should be timely. Generally, it begins when the main vine is 40-50 cm long and the lateral vines are about 15 cm, and thereafter once every 3-5 days; second, no matter which pruning method is used, it should be carried out carefully before fruit setting, and generally no more pruning is done after fruit setting, so that more branches and leaves can provide nutrients for fruit growth. When the fruit begins to expand rapidly, in order to prevent excessive vegetative growth, pinching can be carried out.
4. Vine pressing. When the vines are 30 cm long, the vines should be trained so that they are evenly distributed, and soil clods should be used to press the vines at the nodes to promote the production of adventitious roots, fix the leaves and vines, prevent mutual shading and root and leaf damage from being broken by wind, and thereafter press once every 5-6 nodes until the vines and leaves cover the bed surface. There are two vine-pressing methods: open pressing and hidden pressing. In rainy areas, soil moisture is high. To prevent vine rot, it is not necessary to bury the entire melon vine in the soil; only press soil clods on the nodes, while the internodes remain exposed on the ground. This is called “open pressing.” In dry areas with little rain, to promote the occurrence of adventitious roots, the melon vines should be straightened and entirely buried in the soil, called “hidden pressing.” To prevent breaking the crisp and tender melon vines, pruning and vine pressing should both be carried out in the afternoon. No matter which pressing method is used, it should be determined according to the plant's growth vigor. Strong-growing plants should be pressed heavily and frequently; weak-growing plants should be pressed lightly and less often. Generally, press once every 5-6 nodes, and press at two places before and after the fruit. Leave 2-3 leaves before and after the female flower retained for fruit unpressed, to prevent water accumulation and fruit rot, or restriction of the fruit as it grows.
5. Artificial supplementary pollination. Watermelon is a cross-pollinated crop that relies on insects as vectors. In rainy weather or when insect activity is low, pollen dispersal is affected and fruit setting becomes difficult. To improve the fruit-setting rate and achieve fruit setting and fruit retention at the ideal node, artificial supplementary pollination should be carried out.
① Female flower selection. When pollinating, choose well-developed female flowers on the main vine and lateral vines. Flowers with thick flower bud stalks, enlarged ovaries, normal shape, and tender green and glossy color are easy to set fruit after pollination and grow into high-quality large melons. Female flowers on lateral vines serve as backup fruit retention.
② Pollination time. Watermelon flowers begin to loosen at 5-6 in the morning, and physiological activity is strongest from 8-10, which is the best pollination time. On cloudy days, pollination time is postponed to 9-11 because flowering is later.
③ Pollination method. Use fresh male flowers that open on the same day and are shedding pollen. Hold the petals toward the flower stalk with your hand, then align the stamens of the male flower with the stigma of the female flower and gently dab a few times. One male flower can pollinate 2-3 female flowers.
6. Fruit retention. Generally, retain the second and third female flowers for fruit setting. For early-maturing varieties, the first to third female flowers may be reserved. After the fruit is set, select and retain one fruit in the order of “two, one, three.” For mid- and late-maturing varieties, the second to fourth female flowers may be reserved. After the fruit is set, select and retain one fruit in the order of “three, two, four.” If the fruit on the main vine does not set, fruit should also be retained on the lateral vines in this order. It is appropriate to retain 1 fruit per plant.
7. Watermelon fruit care. During the flowering, fruit-setting, and fruit-development stages of watermelon, careful fruit care is also a key link in improving watermelon yield and quality. Care measures include protecting the fruit, cushioning the fruit, turning the fruit, standing the fruit upright, sunning the fruit, and covering the fruit.
From female flower opening to around fruit setting, the ovary and young melon epidermis tissues are very delicate and susceptible to wind, insect bites, and mechanical damage. At this time, paper bags, plastic bags, etc. should be used to cover the young melons, called fruit protection. When the fruit grows to 1-1.5 kg, break up and level the soil clods under the melon, and cushion it with grass or fine sandy soil; this is fruit cushioning. Turning the fruit means continuously changing the part of the fruit touching the ground so that the melon surface receives uniform light, the peel color is uniform, and the flesh ripens evenly. Fruit turning is generally carried out in the mid-to-late fruit-swelling period, once every 5-6 days, for 2-3 times. Fruit turning should be done on a clear afternoon when the moisture in the melon stalk has decreased and it is not easy to break. Operate with both hands. The angle of each turn should not be too large; it is enough to expose the ground-contact side, so as to avoid twisting and breaking the melon stalk. Each turn should be in the same direction. A few days before the watermelon matures and is harvested, the melon can be stood upright to help the fruit shape become round and proper and the rind color well colored. Otherwise, the ground-contact area cannot receive sunlight and appears yellowish-white, which not only affects the fruit appearance, but also makes the rind thickness uneven, the fruit flavor weak, and the quality poor.
For sunning and covering the melon, the principle is “sun when young, cover when ripe.” In the immature green rind, there is a large amount of chlorophyll, and the photosynthetic products it produces are directly transported to the fruit, promoting sugar accumulation, so it should be sunned when young. When the fruit is about to mature, the chlorophyll in the rind gradually decomposes, photosynthesis declines, and the interior of the fruit is mainly undergoing transformation of organic substances rather than manufacture and accumulation. If directly exposed to strong light, it is prone to sunscald, so when the fruit is about to mature, it should be covered with leaves.
8. Watermelon ripening acceleration. When it is necessary to bring watermelon to market earlier, ethephon (2-chloroethylphosphonic acid) can be used for ripening treatment. The treatment method is: when the fruit size has reached full size but is not yet ripe (that is, 25-29 days after flower drop), apply a 200 mg/kg ethephon solution evenly along the melon surface once per kg of watermelon in the evening. A small amount of neutral soap powder may be added to the solution to increase adhesion. It can be harvested for market two days later. Treated fruits can be supplied to the market 3-5 days earlier than naturally ripened ones, and not only is the quality not reduced, it is actually improved.
9. Disease and pest control. The main diseases of watermelon include Fusarium wilt, anthracnose, viral disease, powdery mildew, and phytophthora blight. The main pests include small cutworms, aphids, red spiders, yellow squash beetles, melon maggots, and leafminers.
① Disease control. Implement a 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, and disinfect diseased holes with lime or 400-fold 50% amobam. In the early stage of disease, drench the root zone with 500-1000-fold 50% amobam solution 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, 500-700-fold 25% carbendazim, 1000-fold 50% zineb, and 1:1:200 Bordeaux mixture every 7-10 days for control.
② Pest control. For small cutworms, melon maggots, and yellow squash beetles, early-spring repeated plowing and harrowing can be used to destroy eggs, sugar-vinegar traps can be used to kill moths and eliminate adults, and 800-1000-fold 90% trichlorfon solution can be used to drench roots or mixed with a small amount of water with fresh grass or roasted aromatic cake fertilizer for bait killing. For red spiders and leafminers, spray 1000-fold 50% dimethoate solution or 1000-1500-fold 80% dichlorvos solution.
6. Harvesting. After pollination, early-maturing varieties mature in about 28 days, mid-maturing varieties in about 32 days, and late-maturing varieties in about 35 days, varying with high and low temperatures. By visual judgment, the tendrils near the melon turn yellow, and the blossom end indentation becomes smaller. Note that when harvesting in high temperatures, harvest 1-2 days earlier to prevent the melon from being overripe and quality declining if it cannot be sold promptly after harvest.
How to identify the maturity of watermelon
1. Calculate. From sowing to harvest, watermelon takes 80-100-plus days. After fruit setting, early-maturing types mature in 30 days, and late-maturing types in 35 days.
2. Look. On a mature fruit, the tendrils on several nodes near the fruit wilt, the fruit stalk fuzz disappears, the stem end is sunken inward, the stripes on the fruit surface spread open, the skin is smooth and shiny, and the bloom has faded.
3. Listen. Tap the melon with a finger. A mature melon gives a dull sound; conversely, a crisp sound indicates an unripe melon.
4. Measure. Determine by the specific gravity method. The specific gravity of a mature melon is 0.9-0.95. One that sinks in clear water is an unripe melon; one with a very large portion above the water surface is an overripe melon. A melon with appropriate maturity has only a small part floating above the water surface.
Watermelon cultivation is quite particular and also requires methods. Only by learning from the experience and methods of successful growers can you avoid detours and grow watermelons with high yield and excellent quality. The market demand for watermelon is very large, so the prospects for watermelon cultivation are still very broad!