Updated: Dec 11, 2020
Everything you need to know to grow healthy, productive, zucchini and summer squash.
My assignment this past week in my Master Gardener class was to troubleshoot a client's problem with their zucchini plant. She was getting dozens of early blooms but no fruit. Any zucchini that did get started wasn't making it and shortly after that fell off. What should she do? Did she need another zucchini for cross-pollination?
Zucchini is one of my favorite vegetables to grow despite the amount of space it demands in my garden. I've grown it for years and all this time without knowing several incredible things about the plant and how to troubleshoot problems that come up in my garden.
The Incredible thing about Zucchini and Summer Squash
Zucchini and summer squash are monoecious, they have both male and female flowers on every plant and do not require other varieties nearby to cross-pollinate.
The female flowers are much larger with the presence of the small green or yellow lump (fruit or ovary) at their base, whereas the male flowers are on much shorter stems. Can you pick out the male and female flowers in the picture from my garden above? The male flower is taking center stage on its tall thin stem. On the female flower, to the left, you can see that the base is the yellow fruit beginning to ripen.
For the female flowers and new squash to develop, the pollen must be transferred from the male flowers to the female flowers from the same species. Squash relies heavily on Honeybees as their primary pollinator. The pollen of squash is too sticky for the wind to help with pollination and other varieties of insects aren’t as reliable as honeybees for carrying the pollen from the male flowers to the female flowers to produce fruit. In commercial gardens, farmers place several hives nearby to ensure pollination.
Honeybees or Hand Pollination
The male flowers are the first ones to bloom with the female flowers appearing later. If you are getting a healthy production of early flowers (male blooms) but no fruit, your problem is likely that there are not enough honeybees around to help with pollination. You may need to help out by hand pollinating your plants. You can use a small paintbrush to transfer the pollen from the male to the female flowers, or you can break off a male flower, remove its petals, and roll the pollen onto the stigma in the center of the female flower. For the best chance of success, use freshly opened male flowers—flowers that open early in the morning— for hand pollination.
Don't Be Fooled, Drooping is a Strategy
Another fantastic and clever thing about Zucchinis, Summer Squash, Melons, and Cucumbers is that they intentionally droop in the heat of the day, curling their leaves up in order to limit the amount of surface exposure of their leaves to the hot sun. Don't be fooled into running for the hose or watering can. Rushing to water a wilting plant in the middle of the day often leads to overwatering resulting in stem rot or misshapen fruit. Instead, visit your garden again in the evening, once the cooler evening temperatures have settled in. If your plants have bounced back, don't water them and stick to your regular watering schedule. If they haven't bounced back water them but don't go overboard.
Conquering Powdery Mildew
The wind transports powdery mildew spores. Remove the affected leaves as they appear. Grow plants in sunny locations. Remove the affected leaves and prune the foliage to ensure good air circulation. And don't overfertilize with nitrogen, which encourages the growth of lush foliage and shade. You can also try spraying the mildew spores off infected plants with overhead sprinkling, but do this midmorning so that the moisture dries rapidly in the afternoon sun. If all else fails, you can try one of the least-toxic fungicides, including horticultural oils, neem oil, jojoba oil, sulfur, and the biological fungicide Serenade.
Sources: UC Statewide Integrated Pest Management Program and the California Master Gardener Handbook.