Have you ever heard about this gardening tip: "Never plant cucumbers next to squash or melons because they will cross-pollinate and the fruit will be off-tasting"? Although it may sound logical, this is not true for reasons that relate to the process of pollination and fertilization.
In short, gardeners need not worry about cross-pollination in their garden as the results of cross-pollination only affect the plants that grow in subsequent years. Poorly flavored melons, squash, or cucumbers are typically due to unfavorable soil or weather conditions, not the result of cross-pollination.
A review of the lesson on the "birds and the bees" may be helpful in understanding flowering, pollination, and fruit development in members of the cucurbit family - squash, melons, pumpkins, and cucumbers.
Monoecious Flowers Require Insects for Cross-Pollination
Cucurbits have a flowering habit that is quite unique among the vegetable crops. They are "monoecious", which means they produce separate male and female flowers on the same plant. The flowers are found in the axils of the leaves. The flowers can be easily distinguished from each other as the female flowers have an ovary at their base that looks like a small, immature fruit.
In order for fruit set to occur, pollen from the male flower must be transferred to the female flower. Honeybees are the principal means by which pollen is transferred from the male flower to the female flower. (The part of the lesson about "bees").
Only Cucurbits of the Same Species Can Cross-Pollinate
Since they have a similar flowering habit, bloom about the same time, and are members of the same plant family, it is logical that gardeners might assume that squash, melons, and cucumbers (cucurbits) will cross-pollinate. Fortunately, however, this is not true. The female flowers of each crop can be fertilized only by pollen from male flowers of the same species. Cross-pollination, however, can occur between varieties within the same species.
For example, cross-pollination can be seen in the squashes and pumpkins. Summer squash, pumpkins, gourds, and some types of winter squash belong to the same plant species, Cucurbita pepo. All varieties within this species may cross with one another. Thus, an acorn squash will cross-pollinate with a zucchini or a miniature gourd. However, muskmelon (Cucumis melo) and cucumbers (Cucumis sativus) belong to different species and will not cross with each other. An example of incompatibility can also be seen in the animal kingdom. Cardinals cannot mate with blue jays despite both being similar-sized birds. (The part of the lesson about the "birds").
When Cross-Pollination Occurs, it Does Not Affect the Current Year's Fruit
When crosses occur between members of the same species, we do not see the effect of the cross in the first year. The genome of the plant determines the qualities of the fruit. However, the seeds inside that fruit are determined by the results of pollination. So, if cross-pollination occurs, half of the seed's DNA comes from one variety and half from another. If the seeds are saved and planted, the plants will produce fruit that will be different from either of the parents.
Once in a while, gardeners will allow a chance seedling to grow in their garden or out of a compost bin. The fruit that develops from these saved seeds may appear quite unusual. Occasionally, one can guess what the parents were by looking at the fruit and/or remembering what was planted in that area of the garden the previous year. For example, a pumpkin-shaped fruit with greenish bumps on it may suggest a parentage of a variety of pumpkin and a green-warted gourd variety.
Common Cucurbit Species Grown in the Vegetable Garden
Only those vegetables that are in the same plant species could potentially cross-pollinate. But remember, even if they did cross-pollinate, it won't affect the quality of this year's fruit. Only the seed inside the fruit will be a hybrid of the two different varieties.
| Species | Vegetables |
|---|---|
| Cucurbita pepo | zucchini, crookneck, straightneck, acorn, scallop, spaghetti, delicata, pattypan, sugar (pie) pumpkin, field (jack-o-lantern) pumpkin, ornamental gourds |
| Cucurbita moschata | butternut, calabaza, tromboncino (zucchetta), Dickinson pumpkin, Long Island cheese pumpkin, Cinderella (fairy tale) pumpkin |
| Cucurbita maxima | Hubbard, buttercup, turban, Kabocha, giant pumpkin |
| Cucurbita argyrosperma | cushaw, kershaw |
| Cucumis melo | cantaloupe, honeydew, muskmelon |
| Cucumis sativus | cucumber |
| Citrullus lanatus | watermelon |
| Momordica charantia | bitter melon |
| Luffa | loofah gourd |
| Lagenaria siceraria | calabash (bottle gourd) |
More Information
- Vegetable Harvest Guide
- Vegetable Planting and Harvesting Times
- Suggested Vegetable Varieties for the Home Garden (publication)
- Reasons for Poor Fruiting of Vine Crops
- Harvesting and Storing Vine Crops
- Crop Rotation in the Vegetable Garden
- Growing Watermelon in the Home Garden
- Growing Cantaloupe, Muskmelon, and Other Melons in the Home Garden
- All About Pumpkins
- Growing Squash in Iowa
- Growing Cucumbers in the Home Garden