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Odd fruits resulted from last season’s cross-pollination

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Jessica Walliser
Though folks often worry about cross-pollination of cucurbits affecting their garden, unless you plan to save seeds, there’s no need to worry about it. Natural cross-pollination will occur but it will not affect the current year’s crop in any way.

Question: I have a small (maybe 15 by 35 feet) garden. I planted three zucchini plants on one end and planted four spaghetti squash on the other end. It seems that the zucchini plants have cross-pollinated the spaghetti squash, as all the “fruit” from the spaghetti squash are green and not the smooth yellow that I was expecting. Is this preventable?

Answer: This is a great question, and it’s one that I get a lot. There seems to be a good bit of confusion about exactly what cross-pollination means and how it can impact a plant’s health and production.

I’ll start with a brief explanation of cross-pollination and then explain how it can influence the cucurbit family in particular, which is the plant family in which both your zucchini and spaghetti squash reside.

Cross-pollination occurs when pollen is moved from the male part of one flower to the female part of a flower on a separate plant. In almost every case, cross-pollination will only occur within the same species of plant. In other words, a carrot flower cannot pollinate a cucumber flower. However, one variety of cucumber can serve to pollinate a different variety of cucumber.

Since members of the cucurbit family, which includes squashes, cucumbers, pumpkins, gourds, melons, and a few other vine crops, seem so similar, many gardeners assume that all of these vegetables are able to cross-pollinate with each other. However, this isn’t the case. Again, the female flowers of each of these crops can only be fertilized by pollen from male flowers of the same species. It gets tricky, however, when you discover that there are several members of this complicated plant family that are, in fact, the same species, though they’ve been selected for different traits and look very different.

For example, cucumbers (Cucumis sativus) and Cinderella pumpkins (Cucurbita maxima) cannot cross-pollinate because they are different plant species. But, summer squash (including your zucchini), many pumpkins, and some types of winter squash (including your spaghetti squash) are all actually varieties of the same species of plant (Cucurbita pepo), therefore they can often cross-pollinate with each other.

Because of this, a zucchini can indeed cross-pollinate with a spaghetti squash. However, when this occurs, you will not see the effects of that cross that same year. But if you collect, save, and plant seeds from that cross-pollinated crop, you’ll see the results the following season; the plants and fruit grown from your collected seeds will be very different from either of the parents. Sometimes this results in some pretty funky plants, which is why most gardeners purchase new seeds of cucurbit crops every year that come from plants whose pollination is highly controlled via the seed grower.

In your case, the spaghetti squash seeds you planted this spring were collected from a fruit that had cross-pollinated with a different variety the season before. Your green spaghetti squash are not the result of cross-pollination this year, but last. Perhaps you saved your own seeds? Or you didn’t purchase seed from a reputable seed company that tightly controls pollination? Whatever the problem was, you can prevent it in future years by purchasing new seeds for all cucurbit crops every year from high-quality seed purveyors.

Though folks often worry about cross-pollination of cucurbits affecting their garden, unless you plan to save seeds, there’s no need to worry about it. Natural cross-pollination will occur but it will not affect the current year’s crop in any way.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.

Send your gardening or landscaping questions to [email protected] or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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