It's not uncommon for male and female flowers to be out of sync. Most of
us plant a number of vines in one planting hole/hill so the odds
increase. Even then, with close to 15 plants this year, I went 3 days at
the beginning of flowering with only females and no male flowers. Then,
after a while, the trend will reverse. Lots of males, few females. I
grow a variety known for less production per plant, so putting in a
number of plants works out fine. I'm averaging 2/day right now... which
is plenty.

Thanks rgreen. That is a great idea. I will try that next year. But I still don't understand why the plant grow with no pollinator.!!

Doing a search on "black open pollinated zucchini" yields only results for Black Beauty zucchini. And looking further into that variety it seems there is some evidence of Black Beauty being somewhat parthenocarpic. Meaning that it can produce fruit without pollination.

Rodney

More often than not, squash will start blooming with just male flowers, because those flowers produce color at low expense of energy and nutrients. That's to begin to attract pollinators. Once that's done, they start spitting out both sexes. Females are harder to make. But occasionally plants get very confused.

Though if the plant knows it's parthenocarpic, it isn't confusion, but just being smart!

That must be it. Somewhat parthenocarpic. The variety is sold by Fedco Seeds as Black Zucchini. I will continue with this variety, as I get tired of the pollination, which perhaps was never necessary.

Do you have any other squash growing nearby? Acorn, scallop, yellow summer? Or any pumpkins or gourds? They are all the same species, Cucurbita pepo, and can pollinate one another.....assuming the pollen gets from one flower to another on some critter that got into the greenhouse.

Two years ago my zucchini didn't produce anything, all the flowers were males. So far the same thing this year, and I have 2 plants. I never thought I'd see the day when I couldn't grow zucchini.

Hi nature girl. I do have some carnival winter squash (Cucurbita pepo) growing outside about 100 feet from the greenhouse. Perhaps they are pollinating, but they just started to flower recently. But that could be part of the mystery and thanks for the thought. And flower girl .... not grow zucchini??? Right???? Who could ever guess. Seems to be not normal to me.

It sounds like your Black zucchini has mutated into a parthenocarpic variety (or else it's not Black—maybe it was an accidental cross). I would save seeds (if you happen to get any male flowers that pollinate them later; if they don't get pollinated, they should be seedless) if I were you and see if they do it again next year.

An open-pollinated parthenocarpic zucchini would be pretty awesome. Lots of people (including me) would probably want your seeds.

An alternate idea is that they mutated and now have perfect flowers like tomatoes, for the most part (so they could self-pollinate with a single flower). It would have seeds then. I've heard of an Asian melon like that, but no squash, yet. Can you get a close-up on the flowers?

That is some really interesting information and ideas Shule. and I will do just that. If I get a male flower, I will hand pollinate and let the fruit grow to set seed. And see if any of the fruit I am getting are growing seeds. I will try to get as close to a flower as I can and post the photo here. I am not an expert photographer, as I just learned how to use my cell phone camera about a year ago......But I will try.... Thanks Peggy

If you are saving seeds, you might want to bag a few flowers.

I will. But I cut open a fairly large zucchini this morning and there were just hints of seeds. So maybe this is really parthenocarpic behavior....!! But if I get a male, and pollinate by hand, I will bag the flowers for sure, as I do have some winter squash outside that could possibly also pollinate.

Here is a close up of a flower, Shule.

I have trouble every year with too few male flowers and have not noticed evidence of parthenocarpic behavior. I typically grow 17 or 18 plants. They all produce a few male flowers early, then almost entirely females. Sometimes I'll have a dozen new female flowers and not one male, or the male will be stunted with no pollen. Sometimes I'll get a spurt of males, meaning 3 or 4 at one time out of 17 plants. But it doesn't last long.

A guy at cooperative extension service told me it might be a calcium deficiency, but I'm beginning to think it has to do with temperature. Adding calcium eliminated blossom end rot but did not increase the frequency of male flowers. June is usually the warmest month in my yard and that's when I get the most male flowers. Has anybody tried increasing daytime temperatures above 70 degrees? Does that help? Perhaps a greenhouse would help?

@HU-402297962

Have you tried plucking off extra female flower to encourage new flowers to come faster? If warm temperatures are helping, extra phosphorus might help in cool weather. Have you tried new varieties of zucchini? You generally want squash to be above 70 degrees in the daytime.

You also might try growing parthenocarpic varieties.

I've a similar problem this year. A couple of male flowers early on but for the last few weeks only females. These are hardly ever pollinated, maybe one in a dozen, possibly via a neighbours plants or from a nearby cucumber, if that's possible? Given the current heatwave it can't be lack of heat. Variety is Fireze which has aways served me well in the past.

Extreme heat can shut down both flowering and pollination. For a while when we were having near 100F highs my female flowers weren't even opening but the males were. Once it cooled down a bit I started getting good pollination. Not sure what would cause only females to show up this late in the season.

I've had precisely the opposite this year. Last year it was the opposite of that. Just rollin' dice. It is, however, well understood that male flowers show up first, because they are easier for the plant to produce, and they attract pollinators for when the females come out.

I had a nice mix of male and female to start - in spring - but now with heat waves the boys are shy and the abundant females producing babies that die on the vine. sigh sigh.

peggyhamill, I have zucchini with only female blossoms that are producing fruit. There's no one else in the neighborhood growing zucchini (I live in an area of condos), so it's highly unlikely they have been pollinated. The fruit grow very slowly, and most stop growing at around 5" long. But currently, I have one growing to full size for which the flower never even matured or opened. I grew the plants from a Tasty Black Patio start produced by Westwind Gardens. Before this happened, the production had slowed, possibly due to hot weather, and I gave them some fertilizer and Morbloom (0-10-10). It's happening with both zucchini plants that came from the same tray of starts.

Mysterious.....more parthenocarpic that we thought I guess....

This shows the harvested zucchini outside and inside. The posted pictures lost some resolution, but you can see the undeveoped pistil in the flower bud.

very interesting and something I had not considered. Thanks Peggy