Zucchini not setting fruit

Asked August 31, 2020, 5:51 PM EDT

To avoid the radical mildew issues we’ve had in the past, I watched multiple YouTube videos about Zucchini growing. I clip off just enough leaves, less than 10% daily, to get airflow through the plant and to expose blossoms to pollinators. So far no mildew, whereas normally I’d be dealing with solid white and dead leaves by now. My problem is that my zucchini loving wife is very mad, because we’ve had only 3 fruits develop so far! Almost all the hundreds of blooms have been “male”, with no swollen stem behind the blossoms. None of the videos I watched eluded to any such production issue. Could my removing a few leaves each day be the cause? I don’t see bees around the blooms even though they’re exposed and airflow is great, although they love our sedum and nearby catmint. I may not survive the summer if my spouse doesn’t get more zucchini. Help!

Clackamas County Oregon

3 Responses

Your zucchini plant looks very healthy. Nice green leaves and stems. It's too bad you're not getting fruit.

There are several possible reasons for not getting fruit, the zucchini variety, pests (though I see no signs of any pests), poor pollination (but you did get 3 healthy squash), irregular water, too much direct sun. What may be the problem is too much nitrogen. Nitrogen stimulates leaf development at the expense of fruit. Pruning also promotes leaf growth. Often with tomatoesand hi nitrogen vertifiler you get big lush plants, but no tomatoes. In the spring a dose of fertilizer with nitrogen will get plants off to a good start. However, once the plants are growing well, if the plants need fertilizer choose one higher in potassium.

Squash are very susceptible to powdery mildew. The best things you can do to prevent this disease are: Good air circulation to dry out the leaves as you have been doing; select powdery mildew resistant zucchini plants; plant in full sun, (powdery mildew spsores can't survive full sun), disinfect all tools with full strength vinegar or 1:9 bleach:water, water in the morning so the leaves dry out during the day, do not water in the evening because it creates moist conditions, and remove any leaves with signs of powdery mildew. Once the leaves have become infected, you cannot cure them, so remove them and dispose of them in the trash. This article has additional information, Powdery Mildew in Curcubits https://extension.umn.edu/diseases/powdery-mildew-cucurbits. Preventitive sprays must be repeated at 7-10 day intervals. This article has some sources of preventative sprays, Squash - Powdery Mildew https://pnwhandbooks.org/plantdisease/host-disease/squash-cucurbita-spp-powdery-mildew. The products with an "H" means good for home use. Hi nitrogen fertilizers also favor the development of powdery mildew, as the fungus readily attacks lush new growth. ,


Thank you for answering, Anne. So far there is no mildew at all. I have to attribute that to keeping the perf hose covered so it can’t spray onto leaves, and clipping the lowest largest leaves so few if any leaves lay on the ground. I also put a tripod over the zucchini and kinda train the main stems somewhat upward and away from the ground. I remove leaves throughout just enough to better expose blossoms and aid anti-mildew ventilation.

To improve tilth over previous years, in addition to last fall’s mulched leaves and aged kitchen compost, I tilled in a healthy stand of cover crop; vetch, peas, crimson clover, oats. I spose that may have added nitrogen, otherwise I infrequently use Lily Miller vegetable fertilizer, and more of that on corn, peppers, tomatoes, peas, and other veggies, not so much on very leafy plants like the Zucchini.

As mentioned, there are tons of blossoms, far more than normal, but behind the blooms are slim stems that some say are “males” that won’t set. The blooms fall off readily. The stems behind female blooms supposedly are swollen due to active gymnosperm(?) and blossoms stay on during fruit development. Do you think that male/female theory has validity?

One fellow said most blooms are male in early season and females blossoms predominate later, but we’re beyond that now. Hundreds of dud blooms, maybe 5 “female” that set, two of which ultimately had failed 3 inch fruit. I don’t see any insects around the blooms, despite my opening up the plant so bees can see the yellow; but if they’re all male blooms anyway, pollinators would make little difference.

I guess it’s possible the Four inch, 3-plant Bonney Plants pot we bought had only 1 “good” plant. And if it was nitrogen, why all the blossoms, albeit duds? But maybe that’s how it works, and for more viable blossoms I should add only potash & potassium, or just bone meal. Perhaps for next year I should avoid planting cover crop where I think the zucchini will be planted.

I may write Bonnie Plants and see what they say. Theirs are supposed to be a higher quality garden plant and guaranteed.

You have a good system for improving the soil with compost and green cover crops. It shows in your healthy zucchini plant.

Squash have an interesting pollination system. First there are the distinctive male and female flowers, as you've seen. The female flowers are only ready for pollination for about 4 hours in the morning, a pretty short window. They require 6-10 visits from a pollinator to fully pollinate all the squash seeds in the squash fruit. Any less and the squash will not fully develop. Several pollinators do this job, squash bees, honey bees, bumble bees, and others. Squash bees, a solitary ground dwelling bee, have evolved to pollinate squashes and are good at it. For one thing they are more active earlier in the morning than honeybees. Attracting pollinators helps all the plants in your garden by being ready to transfer pollen when times are right. This article has a good description of this process, The Unique Pollination System of Cucumbers, Melons and Squash https://blog-yard-garden-news.extension.umn.edu/2020/06/the-unique-pollination-systems-of.html.