NC Cooperative Extension

Cross Pollinating Crops

Cross Pollinating Cropsproduce logo

Sources:  Heirloom
Vegetables, Clemson Univ., http://hgic.clemson.edu/factsheets/HGIC1255.htm
Wikipedia, http://www.wikipedia.org/

Home vegetable gardeners are often concerned that planting similar crops too close together will cause one vegetable to contaminate the other through cross pollination.

If you plant a cucumber beside a squash will you end up with a cuash or a squcumber?  This is not a problem with vegetables that are different species even if the vegetables are similar.  Cucumbers and squash are both in the cucurbit family but cucumber (Cucumis sativus) cannot cross pollinate squash (Cucurbita pepo) because they are two different species.

However, varieties of the same species can cross pollinate.  Yellow summer squash and zucchini are the same species, (Cucurbita pepo), and will cross pollinate.  This cross pollination will not affect the fruit that the plants produce this year but if you save the seed it will affect the fruit that come from that saved seed next year.  If you plant squash and zucchini close together and save the seed from either then the fruit from that seed may have characteristics of both.  This is especially true of plants that are pollinated by insects or by wind.

Different varieties of sweet corn will also cross pollinate.  Sweet corn is the exception to the rule of cross pollination not affecting the crop in the current year.  If you plant two varieties of sweet corn close together then the seed may have characteristics of both parents in the current year.  For example, if you plant a yellow and a white corn together and they cross pollinate the ears of either variety may have mixed white and yellow kernels.

If you buy commercial seed then you don’t have to worry about cross pollination.  Commercial seed producers go to great lengths to make sure that varieties of the same species are not cross pollinated and that what you buy is what you get.  Saved seed is a different matter.  Many people like to grow heirloom varieties that are not available commercially.

If you save seed from your garden then you have to take steps to make sure that your seed supply is not cross pollinated by another variety.  Heirloom Vegetables a publication from Clemson University tell us that “Some vegetables are mainly self-pollinating; their seeds will produce plants like the parent plant that produced the
seeds.  Beans, peas and peanuts, lettuce, eggplant, peppers, and tomatoes are usually self-pollinating.  Insects occasionally cross them, so plant them with at least 10 feet between varieties.

Beans and tomatoes are very popular as heirloom vegetables partly because they are easily maintained true to type.  Vegetables that are cross-pollinated by insects or by wind need to be isolated or raised at a considerable distance from other
varieties.  This distance may need to be several hundred yards or more, depending on the crop.

Onions, cucumbers, corn, pumpkins, squash, broccoli, beets, carrots, cabbage, cauliflower, melons, radishes, spinach, Swiss chard and turnips are all insect-or wind-pollinated.  In a small garden, the easiest way to ensure purity is to grow not more than one variety of a species at a time.  If your goal in raising an heirloom variety
is to preserve it, you do not want it to cross with something else.

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