Heat can squash your zucchini before it fruits. Here is what to do
Q: My zucchini squash won't bear fruit. The plant is big and lush and is producing lots of flowers — even some tiny baby squash that wither and fall off without developing. I have heard the gardener jokes about how zucchini plants produce so much that you resort to forcing squash upon all visitors. What is wrong with my squash plant?
A: Plants in the cucurbit family — cucumbers, gourds, melons, pumpkins and squash — tend to have pollination problems, especially if you only have one plant or few pollinators.
Plants in the cucurbit family produce both male and female flowers blossoms on each plant. The male blossoms are small and on a slender stalk. The female blossoms are generally larger and have visible fruit below the blossom, this is most likely the tiny baby squash that you report seeing on your zucchini plant. The female flower must be pollinated in order for fertilization to occur and the little fruit to continue to develop. If the flowers are not fertilized, then seeds will not develop and the squash plant will abort the little squash.
Early in the season gardeners often become concerned when the first flowers appear and fruits fail to set, but that's because, with many of the cucurbits, the early flowers are all males. Until the female flowers develop, somewhat later, pollination can’t occur. This does not sound like the issue in your case as it sounds like you have both male and female flowers.
There are usually three causes for poor fruit set on your zucchini:
1. Poor pollination due to a lack of pollinating insects to move the pollen from or sterile pollen.
Squash flower pollen is heavy and sticky, so it requires bees or other insects to transfer it from the male flower to female flowers.
Also each female squash blossom requires several hundred grains of pollen to be properly fertilized, so this can require seven to 10 visits from a pollinator. If there are not many insects buzzing around your garden you may need to give the pollen a helping hand.
To hand pollinate, break off a male flower, peel back petals and rub the flower on the female flower — or use a Q-tip or small paintbrush with soft bristles — to transfer pollen from the male flowers to the female flowers. Do this early in the morning while the blossoms are open. Blossoms are only viable for one day. The trick is to be able to differentiate between male and female flowers.
2. Very hot or very cold weather when flowers are blooming.
Weather extremes can limit pollinator activity, and in the case of hot weather may cause the pollen to become sterile.
This year we have had extremely hot weather so that maybe causing your poor fruit set. If you suspect this is the cause, try watering deeply in the morning and shading the plant in the afternoon to keep soil and plant canopy temperatures cooler.
3. Wet weather or overhead watering early in the morning.
This can affect the quality and quantity of the pollen. It's best to water only the soil and not the squash plant.
The Shasta Master Gardeners Program can be reached by phone at 242-2219 or email email@example.com. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.