Mother Nature has given us everything we wanted this spring and summer: lots of water and heat. Problem is that the water and cold weather lasted too long and there was a wee bit more heat than some of the tomatoes, squash, cucumbers and melons could handle when they were flowering. As a result, pollination and the formation of fruit lagged.
This year, nothing really started growing until early July when it warmed up. As a result, heat-loving vegetables didn’t really start blooming until almost the end of the July. By then, we were into a string of 90-plus-degree days that affected the plant’s ability to release pollen and pollinate the flowers. The heat also slowed down the pollinating insects such as honey bees.
Tomatoes are wind pollinated. Each flower has both male and female parts and is therefore self-fertilizing if pollen is present. Under normal conditions pollen is produced when the night temperatures are between 55 and 75 degrees. If night temperatures are below 55 degrees or above 75, the temperatures interfere with the formation of the pollen tubes and pollen can’t get to the ovary to properly fertilize it. Our night temperatures were cold in late July.
High daytime heat can also affect tomato set. Tomatoes tend to release the most pollen between 10 a.m. and 4 p.m. If the day is hot and the humidity is very low, the pollen becomes too dry and doesn’t stick to the stigma. No pollen, no fruit.
So as our summer weather winds down and we begin to face the threat of frost, we need to help the tomato plants shake loose as much pollen as possible to set more tomatoes. One method is to use an old electric toothbrush to vibrate the stalks of the tomato flowers. The vibrations mimic the wind and shake loose a large amount of pollen that will then find its way to the stigma.
On the other hand, cucumbers, melons and squash – otherwise known as the cucurbits – are pollinated by bees. Like tomatoes, the cucurbits need warm soil for rapid growth. Because it was cold into July, they were only beginning to grow when the weather changed. As a result, they didn’t start flowering until early August about the same time the 90-degree days showed up.
The cucurbits have both male and female flowers on a plant. The male flowers bloom 10 days before the female flowers to attract the bees so they are around when the females bloom. Unfortunately, when the female flowers finally bloomed, it was too hot for the bees and fruit set was limited.
To improve fruit set, you can hand pollinate the cucurbits. Using a small soft brush, pick up some pollen from a male flower and brush the pollen onto the stigma of the female flower. The female flower will have a swollen base below the flower. You can also pick a male flower, pull off the petals and then brush it against the stigma of the female flower.