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.