Knowing when watermelon flowers blossom, how they pollinate, and how different variables affect pollination can help you have good watermelon yields in most any weather and season. Knowing the difference between a male and female flower is a good place to start.
Watermelon Flowers – Male Vs. Female
To tell the difference between a male and female flower on a watermelon plant look directly behind the flower. Behind a female flower there will be a bulge. That bulge behind the flower is the ovary that once pollinated will begin to grow into a watermelon.
Male flowers blossom first on the watermelon plant 7-10 days before female flowers appear. Male flowers falling off of the plant is normal.
How Long After Flowers Appear Until You Get a Watermelon?
It will take about 50 days once the first flowers start to appear on the plant until you harvest a watermelon. Once an ovary behind a female flower reaches golf ball size you know the watermelon flower has been successfully pollinated. From this stage it will take 30-40 days to grow into a ripe watermelon.
To learn more about this check out “How Long Does It Take to Grow Watermelon?“
Do You Need Two Watermelon Plants For Pollination?
You only need one watermelon plant for successful pollination. A watermelon plant is monoecious, meaning it has male and female flowers on the same plant, and “self-fertile” meaning a male flower can pollinate a female flower from the same plant.
This is different than a “self-pollinating” plant which has male and female parts in the same flower. Some plants have developed mechanisms to avoid pollinating flowers on the same plant like shedding pollen at a different time than the female flowers are ready.
Commercial Watermelon Growers Use Rented Bees for Pollination
This is a sample agreement between a farmer and beekeeper. Farmers and beekeepers work together to make watermelon pollination in the field a success.
Farmers have to be careful about spraying pesticides around this time because that could damage bee colonies and beekeepers need to be up front about their bee colonies populations because they can range between 10,000 and 60,000 bees and help the farmer with any other information they need like where to place the colonies for best results.
In general, 8 visits by honey bees and 500-1,000 pieces of pollen are needed for successful pollination of a female watermelon flower.
Bumblebees are about 10x more efficient than honey bees at pollinating because of their speed, size, and endurance.
Bumblebees start earlier and finish later than honey bees and because they are bigger can fly in windier and wetter conditions than honeybees. Their wings also cause movement of pollen that can aid pollination. Commercial rentals of bumblebees is not done to my knowledge.
Growing seedless watermelon varieties requires more honeybees and more visits per flower, 16 to 24, for successful pollination. This is because the pollen produced by the male flowers of seedless varieties is not viable.
The farmer has to put a seeded variety in the field with the seedless variety at a rate of about 1:4 so that the seeded variety is there to provide viable male pollen in the field to pollinate the female flowers.
Another reason a farmer might need more bee colonies than usual is flowers near their watermelon crop that are attractive to the honey bees. Wild flowers can distract the bees away from the watermelon field. The farmers answer is just to arrange to have more colonies of bees in the field. More colonies produce higher pollination rates.
Watermelons & Cross Pollination
Watermelons will only cross pollinate with plants of the same species, lanatus. So basically, different varieties of watermelons are what will cross pollinate with watermelons in the garden. Not cucumbers or cantaloupes or any other melon of a different species.
Cross pollination will not affect the watermelon fruit in any way but the seeds inside the watermelon fruit will contain genes from both plants and produce a hybrid offspring.
So preventing cross pollination should only be a concern for you if you want to collect seeds from your watermelon to grow for next year.
To avoid cross-pollination definitively put a bag over the watermelon flowers to prevent pollen from reaching the female flowers. Then hand pollinate the female flowers with the pollen from the variety you choose and place the bag back over the flowers to prevent pollen from another variety access.
Watermelon Pollination Pitfalls to Avoid
Watermelons are insect pollinated. So if you live in a space without much insect activity, like a balcony, or the weather reduces insect activity during the pollination phase of your watermelons you should hand pollinate the plant.
Cold weather below 60 degrees or hot weather above 85 degrees will slow down insect activity. Cloudy weather and rain will also hamper insect activity. This type of weather for a few days or more can cause low pollination rates.
During these times hand pollination is a good idea. It’s simple to do. Take a paint brush or this thing and swirl it around the inside of the male flower and then the female flower.
Does Webbing and More Pollination Mean Sweeter Watermelon
I found no conclusive answer to this question. “More webbing on the watermelon = the more times it was pollinated by bees and the sweeter it will be”
Through my search I saw this statement probably twenty times with no facts or research cited. It seems to me that if this were true you could just hand pollinate watermelons over and over and end up with the sweetest watermelon ever.
Watermelons sweetness is measured in brix. 1 brix equals 1 gram of sugar per 100 grams of liquid. This brix refractometer can be used to measure your own watermelons sweetness levels.
You might be interested in “How To Grow Sweeter Watermelon“.
I did see an article that said hand pollination is not as successful as insect pollination. I’m not sure if this is true. You can hand pollinate over and over as many times as you like.
Comment below with your own thoughts and experiences about watermelon flowers and pollination.