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. 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.
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".)
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 or other members of the Cucurbita genus. An example of incompatibility can also be seen in the animal kingdom. Cardinals cannot mate with blue jays despite both being simlar-sized birds. (The part of the lesson about the "birds").
When crosses occur between members of the same species, we do not see the effect of the cross in the first year. However, 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 pumpkin and green-warted gourd.
Gardeners with a small plot need not worry about cross-pollination when planting cucurbits in their garden. Poorly flavored melons or cucumbers are usually due to unfavorable soil or weather conditions, not the result of cross-pollination.
Updated from an article that originally appeared in the August 23, 1996 issue, p. 148.