Pollination

A poor fruit set in watermelons is usually a result of poor pollination. Watermelons bear separate male and female flowers on the same plant (monoecious).

When flowering begins in watermelon, male flowers will be produced at every node while female flowers will be produced approximately every seventh node.
Pollen must be transferred from flower to flower by pollinating insects - primarily honey bees. For proper pollination, a female flower should receive eight or more bee visits. Insufficient pollination results in misshapen melons.

Flowers open one to two hours after sunrise. Female flowers are receptive to pollen throughout the day although most pollination takes place before noon. In the afternoon the flowers close, never to reopen, whether pollinated or not.

Watermelon flowers are not nutritionally attractive to honeybees; therefore, blooming weeds or other crops can out compete watermelons in attracting honeybees. Destroy nearby flowering plants that may be attractive to honeybees. This will ensure that the bees work the watermelon flowers exclusively.

Since numerous visits are required to each flower during a relatively short period, it is necessary that sufficient numbers of bees be available near the field. It is recommended that at least one honey bee colony be introduced for every acre during the blooming period since native bee populations may not be adequate, or may not coincide properly with the blooming period.

Common causes of poor fruit set include lack of bees for pollinating or cool, wet weather that slows bee activity during bloom.

Bees require water for survival and their efficiency may be improved by a water source near the hives. Some shade may also be beneficial.

When flowers are developed on the plants, do not use insecticides, which are extremely toxic to bees, and apply them at dusk after the bees have bedded for the night.

Q. Do watermelons readily cross with other vine crops resulting in off-flavor and poor quality fruit?

Watermelon varieties readily cross with each other and with the wild watermelon. Watermelons will not cross with cantaloupes, cucumbers, pumpkins or squash. Off-flavor or odd-shaped fruit is generally caused by growing conditions and not cross-pollination.

Pruning

Watermelon plants need to be pruned of excess fruit to allow the correct number of fruit to properly develop and obtain marketable size.

Pruning is performed to achieve a balance between vine growth and fruit set. Pruning increases average fruit weight while reducing the number of unmarketable (cull) fruit.

Pruning should occur in two stages:

The first pruning removes all of the unmarketable fruit (Remove misshapen and blossom-end rot fruit).

While the second removes the late set fruit in order to increase the size of the remaining melons.

There should only be two fruits per vines of varieties, which produced large size fruits and 4-6 in the case of small-fruited varieties after pruning.

To avoid disease spread, do not prune melons when vines are wet.

Fruit in contact with soil may develop rotten spots or be damaged by insects on the bottom. Place a board or several inches of light mulching material, such as sawdust or straw, beneath each fruit when it is full-sized.

Turning

Turning:

Watermelon vines need to be ‘turned’ or adjusted along the rows 25 days after planting to facilitate watering and weeding but main vines should not be touch anymore.

Weed Control

Watermelons, as with most crops, require early season weed control to ensure a quality crop. Watermelons should be kept free from weeds by shallow hoeing and cultivating.

Weed control is essential for good yield and it makes harvesting easier. In addition, the spreading nature of this crop makes weed control difficult once the vines begin to form.

Shallow cultivation by off baring, 15 days after planting followed by hilling up at 30 days after planting and hand weeding thereafter until the crop have attained sufficient size to cover the soil which in turn will suppress the growth of weeds.

Most of the pre- and post emergence herbicides are phytotoxic to the seedlings or reduce plant growth. When this herbicide is used for control, it should be applied to weeds 3 days before watermelon seeding.

Irrigation

Watermelons, with their long vines and large leaves, have high rates of water loss via transpiration. Consequently, they benefit from supplementary irrigation, especially when grown on light, sandy soils.

Heavy soils that have been soaked just before planting may contain sufficient moisture for average crops of watermelon without the need for additional irrigation. Watermelon has deep roots and can survive relatively dry conditions.

Melons are drought tolerant. The plants are deep rooted. Growers with limited irrigation capabilities can often increase yields with only one or two irrigations. However, they require uniform irrigation for optimum growth and yield

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Critical periods, when moisture stress is most harmful, are:

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  Before seedling emergence: Inadequate moisture at planting results in poor and uneven emergence.
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  At early bloom: Moisture shortage at bloom results in poor fruit set and misshapen fruit.
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  The last ten days before harvest: Moisture stress close to harvest greatly reduces melon size and results in rapid vine decline.

Excessive irrigation after the melons have been water stressed may result in fruit splitting.

Avoid irrigating in the late afternoon or at night to reduce foliage diseases. Do not allow the fruits to get wet while irrigating.

Reduce irrigations as fruit reach harvest stage. Watering during the ripening season may delay harvest, cause splitting and reduce sweetness. Two weeks prior to maturity irrigation should be stop.

Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.

Watermelons respond very favorably to drip irrigation. Applying water regularly, will increase fruit set, fruit size, and yield.

Fertilization

Watermelon responds well to fertilizers, especially to organic matter. The amount required depends on the nutrient status of the soil. In general application at a rate of 20–30 t/ha organic manure, 50–60 kg N, 10–15 kg P and 20–30 kg K per ha is suitable for good performance.

A soil test is recommended for each field to be planted. The fertilizer doses to be applied depend on variety, fertility of soil, climate and season of planting. Changes in bed spacing often lead to needed changes in fertilizer amounts.

Generally well decomposed FYM (15-20 t/ha) is mixed with the soil during plough.

The recommended dose of fertilizer to be applied per hectare is 100 kg N, 50 kg P2 O5 and 50 kg K2 O.

Watermelons are a relatively long-season crop; therefore, applying fertilizer in small amounts several times throughout the season will maximize production.

Current recommendations include applying All required phosphorus (and should remain available throughout the growing season because it is relatively immobile in the soil.) plus one third of the N and K before planting and following this with two more applications at 3 and 6 weeks of the remaining N and K.

It is better to complete all the fertilizer applications just before the fruit set.

Planting

Direct seeding is the most common method of planting. In cooler climates, it may be necessary to start the seedlings in a greenhouse to ensure good germination.

Seed rates per ha are 1–2 kg for direct-seeded and 0.3–0.5 kg for transplanted watermelon.

Plant spacing requirements vary depending on variety selection, growing area, time of planting, and soil type, but should be around 60-90 cm and approximately 2 meters between rows.

A. Direct seeding:

Watermelon seed should not be planted until soil temperatures are warm enough to ensure rapid germination. Plant after the soil is warm and when all danger of frost is past.

Triploid plant population density should be 10 to 20% less than that recommended for production of standard watermelon varieties.

Per hill, 3–4 seeds are sown at a depth of 3–4 cm; 3–4 weeks after sowing, at the 2–4 leaf stage, seedlings are thinned to 1–2 per hill (Thinning is practiced 15 to 25 days after sowing). The plants should be thinned to one plant per hill (two if selection is not good).

Seed will remain viable for at least 8 years when stored dry at temperatures below 18°C.

There is no seed dormancy in cultivated seed- and watermelons, but germination is retarded under high temperature regimes.

Germination can be accelerated by pre-soaking in water for 24 hours after scarifying the seed at one end, especially for cultivars that have a hard seed coat. When planted in warm soil, seedlings will emerge in a week or less.

Use fungicide-treated seed. Watermelons are subject to damping off and decay in cool wet soils.

B. Transplanting:

Transplanting watermelons offers several advantages:

1- Plants can be produced under greenhouse conditions when outdoor conditions are not conducive to plant growth.

2- Seed-use efficiency increases, which is especially important with costly hybrid and triploid seed.

3- Soil crusting and damping off, detrimental to seedling growth, can be eliminated or reduced.

4- Planting depth is uniform.

5- It usually results in earlier harvests.

6- It is the only cost-effective way to grow seedless watermelons.

Watermelons suffer transplant shock if the roots are even minimally disturbed. So seedlings must be grown in containers such as peat pots, Speedling trays, or Jiffy pots to be successfully transplanted.

Sow seeds in small plastic pots or containers using a potting mix that has good water-holding capacity and good drainage such as peat moss, commercial potting soil, or a potting mix prepared from soil, compost, rice hull, and vermiculite or sand.

Sow one to two seeds per container for open-pollinated varieties and one seed per container for hybrids to reduce seed costs. Pinch off or cut seedlings to avoid disturbing the roots. Do not pull seedlings out of the container to thin.

1- Watering:

Uniformly moist media will ensure good germination, but overly wet media will encourage damping off and high seedling mortality.

Established transplants should be watered only when necessary. Excessive watering leads to succulent plants with restricted root growth. Water should be applied only when the surface of the media is dry to the touch.

As plants grow larger, their water needs will increase. They may need water daily when approaching transplant size. The media should be moistened thoroughly until water drips through the container’s drain holes.

Water the seedlings in the morning, to allow the foliage to dry before night. Wet foliage encourages disease.

2- Fertilizing:

Plants are fertilized every three days with a solution containing 50 ppm N from Ca(NO3)2 and KNO3 from cotyledon expansion until the first true leaf is fully expanded, then with a 200 ppm N solution applied every other day until the second true leaf is fully expanded, finally the fertilizer is reduced for several days before transplanting to the field.

3- Hardening-off:

Watermelons need not undergo a long hardening-off period; three to four days are sufficient.

Hardening-off can be initiated by reducing greenhouse temperature and by withholding water or limiting fertilizer. Hardened plants are more able to withstand chilling stress, mild water stress, drying winds or high temperatures. Hardened plants generally produce new roots more rapidly than unhardened plants.

4- Planting:

Plants generally will take three to five weeks to be field ready depending on variety and growing conditions. Plants grown under less than ideal conditions will take longer to produce.

Seedlings are ready for transplanting when they have 2 or fewer true leaves at the time of transplanting. Older plants establish very slowly in the field.
Bare-root plants will not survive so pull seedlings with their root balls intact before transplanting.

Transplant seedlings into the field at spacing similar to those used for the direct seeding method.

Transplants should be watered as soon as possible after transplanting to remove air pockets surrounding the roots and to ensure sufficient soil moisture for good root establishment.

If you grow seedless melons, you must also plant a row of a standard seeded variety for every three rows of the seedless melons. The seedless melon varieties do not have the fertile pollen necessary to pollinate and set the fruit.
Use a starter fertilizer solution when transplanting. Use a water-soluble fertilizer such as 10-34-0. Mix 1 quart of this material in 50 gallons of water.