How to Successfully Grow Seedless Watermelon

Seedless watermelon growth requires much more management and attention to detail, than the growing and production of regular seeded watermelons. Some extra steps are necessary to make sure the pollination and yields are right.

Watermelons without seeds are not self-pollinating, pollinizers, or diploid watermelon crops. Henceforth, they must be included in production to provide pollen. Bees then naturally transfer the pollen to flowers of the seedless melons.

Extension Fruit and Vegetable Specialist at the University of Delaware, Gordon Johnson, is an expert on seedless watermelon production. He stresses the importance of healthy transplants, the science behind using pollinizer crops, as well as the disease and pest control and management.

Strong Start

The successful seedless watermelon production starts with the healthy transplants. After selecting types that can adapt to your area, make sure that the transplants are hardened off, meaning that they should be properly acclimated to the outside conditions before the actual transplanting.

If you are not the one growing your transplants, Johnson says to pay attention what climates your transplants are from, as well as how far they have travelled. “A lot of our transplants come out of southern greenhouses, and while the plantings are good quality, the climate is hot down there and plants don’t get a good hardening off. That can be an issue as they come into our area.”

Next, the transplants should not be too “leggy” or overgrown. This can potentially damage the plant while transplanting.

How to Successfully Grow Seedless Watermelon

Protecting Your Crop

Once you establish the transplants, it is very important that your crops be protected from all of the stressors of the environment.

Johnson says, “Early production is the most subject to variable weather. You can have cold snaps and rainy periods, and that really can create challenges in pollen transfer with bees. Honey bees aren’t as active during stormy weather when it’s cold, or when high winds are active”.

To manage damage from the wind, plant windbreaks, plantings of grains like wheat or barley.  These tend to grow 5 feet tall, and when placed on either side can protect against wind damage. “If you have windy weather during early flowering and fruit development, you’d get less bee activity, less fruit set, and damage to the plant from it being whipped around in the wind.”

In addition, provide sufficient pollination by introducing more hives in different locations throughout the field where the melons are growing. “That early stress also can affect the male flower production, so having some extra pollen out there would be a good insurance policy,” says the expert on the matter.

Managing Pollinizers

You have to use pollinizer crops in order to guarantee fruit development in the production of seedless watermelon.

“In order to pollinate you need pollen from a male flower. The male flowers on the seedless watermelon have a very limited amount of viable pollen so it has to come from a seeded or diploid-type watermelon. They produce the male flowers, and that pollen is then transferred to the female flower.”

Adding pollinizers into the practice of production is potentially tricky, because you have to make sure that they are both vigorous enough to produce flowers, and not competitive when it comes to resources. “Over the years we found that a ratio of 1:3 (pollenizer to seedless) is the best combination. That way you’re not taking up too much space with the plants that aren’t producing the watermelons, and you’re producing enough pollen.”

Earlier, pollinizers were planted alongside seedless crops in a separate row. Currently, it is recommended to plant them s in the same row, as this will result in the pollen source being closer to the crop.

Some growers also use the technique of co-planting pollinizers with the seedless crops. They do this during the stage of transplanting, to make it more precise for the workers.

Johnson explains here, “The previous system required workers be trained to know what they were doing, and every now and then we would see fields where the pollenizers weren’t planted correctly. This way the industry made it fool proof, and, for the most part, it looks like it’s just as effective yield-wise.”

Adequate Pollen

The key is to make sure there is enough pollen transfer at the beginning of production, in order to ensure an adequate fruit setting.

“We found that the bare minimum [for pollination] is 500 pollen grains; however, to get a proper fruit set with no quality defects, you’ll need at least 1,000.The pollination-like event is critical, and if it doesn’t happen properly you’ll get no fruit, smaller fruit, or fruit with defects. Part of my research shows that if you have inadequate pollen, it can increase the risk of hollow heart, so you have to make sure this whole series of events is occurring well.”

Managing Pests and Disease

When it comes to defending the crops, Mr. Johnson’s growers in Delaware had to deal with mites, gummy stem blight, anthracnose, powdery mildew, and downy mildew.

He shares their experience here, saying, “One of the downfalls of windbreaks is that they also attract mites. Once you kill them, the mites that are in that material will go right to the watermelon,” he warns.

As far as managing diseases, Johnson suggests implementing a loose rotation. Watermelons build up diseases very quickly. I have a few people who will grow two crops of watermelon one year and one the next. That second year there will always be more disease and the yield is always lower. If you are unwise enough to grow a third year you could create massive losses.”

Grafting is an Option

Our expert in the article also talked about the possibility of introducing grafted plantings. They will bring resistances into the rotation which helps to manage diseases. Although grafted watermelons are more common in Europe, Asia, and the Middle East, research in Florida and South Carolina has shown some promising results in favor of adopting grafted technology in the USA. If the plants stay healthy, the growers will get two plants to harvest at least.

How to Successfully Grow Seedless Watermelon

“With standard seedless 15-pound watermelon, better plantings will carry three, or even four to harvest. If you’re carrying less than two watermelons per plant, then there’s something that’s stressing out the plant.”

Johnson has seen in his work that growers harvest six or seven times one field, if the plants are as healthy as possible. The average harvest is 50,000 pounds, however some fields produce nearly 100,000 pounds thanks to proper management and care from the very start to finish.