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From acorn to zucchini

by Guest Poster on May 5, 2010

in Food, Gardening

This guest post was written by David Deardorff and Kathryn Wadsworth, authors of What’s Wrong with My Plant?, and originally appeared on their blog.

Every spring I’m frequently asked two questions by gardeners in northern states. The first is, “Why doesn’t my zucchini grow? It just sits there. What’s wrong with it?”  The second common question I get is, “What’s wrong with my zucchini (or cucumber, or melon)? It has lots and lots of flowers but no fruit. What’s up with that?”

Home gardeners love to grow members of the squash family, the Cucurbitaceae, called cucurbits for short. This big, important family includes all types of squash: winter (like acorn and butternut), and summer (like zucchini). It also includes cucumbers, pumpkins, melons in the genus Cucumis (cantaloupe, Persian, honeydew, casaba) and watermelon, in the genus Citrullus.

Keep in mind one very important fact about all these delicious vegetables and fruits:  they are all warm season crops. This means that they are sensitive to cold temperatures. And this sensitivity can cause stunting and lack of fruit.

Vegetable starts of warm season plants are readily available in nurseries and garden centers early in the season, when temperatures are really still too cold for them to thrive. As a result, when gardeners plant them too early, the plants simply sit, growing slowly or not at all, and become stunted. They usually begin to grow well when the weather warms up. So the answer to the first question is the squash doesn’t grow because it is still a bit too cold for it.

These two summer squash, each about 3 inches tall, wait for warmth. They’ve not grown significantly in the two months since they were planted. The photo also illustrates the second problem that crops up this time of year. Both plants above are flowering, but all the flowers are male. Male flowers do not make fruit. Only female flowers make fruit. All members of the squash family have female and male flowers on the same plant, but they produce only male flowers early in the season while temperatures are still cool. They start producing female flowers later in the season.

Here’s a female cucumber flower. See the spiny baby cucumber holding this flower up? That fat spiny structure below the petals (that is, closer to the plant) is the ovary of a female flower. The ovary is the thing that matures into a fruit, whether it’s an acorn squash or a zucchini. No female flowers, no fruit! And that’s the answer to the second question.

Look at the stalk holding up this male zucchini flower. It doesn’t look like a miniature zucchini at all. That’s because it isn’t. This stalk is merely a stalk. This flower does not have an ovary because it is a male flower and it will never mature into a fruit. The male flowers produce the pollen needed to fertilize the female flowers.

A female flower of a yellow summer squash clearly has a large yellow ovary underneath the flower petals. The ovary looks like a miniature squash. After the female flower gets pollinated it matures into a delicious squash.

Next time you wonder why your cucurbit plants sit and sulk, or your zucchinis make flowers but no fruit, just be patient. Keep your vegetable starts where they are warm and have plenty of sun. Put them outside in the garden or a container when the weather warms up.

{ 3 comments… read them below or add one }

1 Dianna June 18, 2010 at 10:40 am

So my squash plants look okay, green not yellowing. I have lots of flowers and lots of little squash. My problem seems to be that the zucchini or crook neck get just a few inches along (3-5″) and then they stop, turn yellow at the end or, in the case of the yellow squash, seem to rot! These plants are in rasied beds with amended organic material and on drip watering. Although milder in temps so far this year it has been into the 80’s. Would appreciat any advice!

2 Dick Wozniak August 10, 2014 at 1:10 pm

My acorn squash plant has some squash that doesn’t look like an acorn but are large and look like football sized watermelons. There is one squash that looks like a regular acorn squash.

3 Brian Ridder August 11, 2014 at 10:25 am

Thanks for the comment, Dick. We’d love to see pics of your harvest.

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