Tactics For Successful Seedless Watermelon Production
Growing seedless watermelon requires greater management and attention to detail than seeded watermelon production, and additional steps must be taken into consideration to ensure adequate pollination and strong, healthy yields.
Because seedless watermelon are not self-pollinating, pollenizers, or diploid watermelon crops, must be included in production to provide pollen, which is then transferred by bees to flowers of seedless melons.
Gordon Johnson, Extension Fruit and Vegetable Specialist at the University of Delaware, provides expertise on seedless watermelon production, touching on the importance of healthy transplants, the science behind using pollenizer crops, and pest and disease management.
Get Off To A Strong Start
Successful seedless watermelon production begins with healthy transplants. After you’ve selected varieties that are adapted to your area, it is important to make sure your transplants have been hardened off, or properly acclimated to outside conditions before transplanting.
If you aren’t growing your own transplants, Johnson says to be aware of what climate your transplants are coming from and how far they’ve travelled to look out for potential stress.
“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,” he explains.
Furthermore, make sure that transplants aren’t too “leggy,” or overgrown, which can create additional damage to the plant during transplanting.
Protecting Your Crop
Once transplants have been established, it’s important to make sure your crops are protected from environmental stressors.
“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,” says Johnson.
To help manage wind damage, he suggests planting windbreaks, which are plantings of grains such as wheat or barley that can grow up to 5 feet tall, on either side of the crop to protect it from 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,” he explains.
Another way to ensure sufficient pollination despite adverse environmental conditions is by introducing more hives in various locations throughout the field.
“That early stress also can affect the male flower production, so having some extra pollen out there would be a good insurance policy,” Johnson says.
Using pollenizer crops is a must to guarantee fruit development in seedless watermelon production.
“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,” Johnson explains.
Integrating pollenizers into your production practice can be tricky, he says, and you have to be sure the pollenizers are vigorous enough to produce flowers, yet not competing with your marketable crops for 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,” Johnson says.
In the past, pollenizers were planted in a separate row alongside the seedless crops. Today, Johnson recommends planting pollenizers in the same row as the seedless, so the pollen source is closer to the crop.
Another technique some growers are employing is co-planting pollenizers with the seedless crops during the transplant stage to make the transplanting process more precise for workers.
“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,” he explains.
Making sure that there is enough pollen transfer at the beginning of production is key to ensuring 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,” Johnson says.
“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
In Delaware, Johnson’s growers have had to manage mites, gummy stem blight, anthracnose, powdery mildew, and downy mildew.
“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,” he explains.
Grafting As An Option
He also mentions the possibility of introducing grafted plantings, which carry resistances, into your rotation to help manage disease. While grafted watermelons are more commonly found in Asia, the Middle East, and Europe, current research in South Carolina and Florida has shown promising results for adoption of grafted technology in the U.S., according to Johnson.
If plants are healthy, growers should see at least two plants to harvest, he says.
“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.”
With a healthy crop, Johnson has seen growers harvest six or seven times in a field. While the average harvest is approximately 50,000 pounds, he has seen some fields produce almost 100,000 pounds with proper management from start to finish.