Can watermelon and cantaloupe cross-pollinate?

Will watermelon and cantaloupe cross-pollinate and produce bad-tasting melons? Is it possible for a vine that had cucumbers growing on it earlier in the season to produce a cantaloupe? I could swear that we now have what looks like a melon on a vine that had cukes before…

The short answer is, no. It’s fine to grow watermelons and cantaloupe side by side. Cross-pollination between melon varieties may occur, but not between watermelons (Citrullus lanatus v. lanatus) and cantaloupes (Cucumis melo ssp. melo v. cantalupo), as they are two different species. In addition, cross-pollination affects not the melon produced that year, but the melons one might grow from any seeds produced inside that melon. According to Sue Stickland’s Back Garden Seed Saving (Chelsea Green, 2001), “commercial seed growers are recommended to isolate melon varieties by 500-1000 meters” or “bag and hand-pollinate the flowers” to keep unwanted hybridization from happening.

The same principle holds true for cantaloupe (Cucumis melo and cucumber (Cucumis sativus): they are indeed in the same plant family (Cucurbitaceae), but they are different species. If your vines were planted close together, you might not have realized there was a melon developing in among the cucumbers–and if you planted the vines from seed, it’s very possible the seed packet contained a surprise cantaloupe!

You may find this information from Iowa State University Extension about cross-pollination among vine crops interesting:
“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 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 a species.”

An article on fruit set in the
Cucurbit family from University of California, Davis (which also has information on how to hand-pollinate plants when necessary) says much the same thing:
“A common misconception is that squash, melons, and cucumbers will cross-pollinate. This is not true; the female flowers of each can be fertilized only by pollen from that same species. Varieties within each species, however, will cross-pollinate.”

Citrullus lanatus, Cross-pollination, Cucumis melo, Cucumis sativus, Seeds

on bitter cucumbers

Some of the cucumbers I am growing and harvesting taste just fine, but some are really bitter—I wonder if I should even be eating them. What causes this, and are they safe to eat (not that I want to)?

What you are describing actually has a name, toxic squash syndrome. It can affect plants in the Cucurbit family (so not only cucumbers but also zucchini, winter squash, and even melons). Here is a Master Gardener article from the Sequim Gazette about cucurbitacin poisoning. A 2012 factsheet (no longer online) from Oregon Health & Science University about this problem says that the cucurbitacins produced by plants in this family may have benefits for the plants themselves, warding off insects. But in humans, excessive cucurbitacin can cause digestive distress. Wild plants tend to have higher levels of this naturally occurring substance than varieties bred for human consumption. Still, environmental factors (such as uneven watering or fluctuations of heat and cold) can cause normally tasty cucurbits to turn bitter.

A 2007 article from North Carolina Cooperative Extension, “What Makes My Cucumbers Taste Bitter,” says that cucurbitacin is mostly found in the leaves, stems, and roots of the plants but it can spread to the fruit as well. In your cucumbers, the highest concentration is likely to be in the skin and just below the surface of the skin. “Misshapen fruits are more likely to be bitter than well-shaped fruits. Some scientists even think that varying levels of fertilizers, plant spacing and irrigation frequency may also affect cucurbitacin levels. Bitterness seems to vary with the type of cucumber grown.”

Because of the potential for unpleasant side effects, I suggest not eating the rest of a cucumber (or any other member of the Cucurbit family) if the taste is bitter.

Garden Tip #108

Keep harvesting all those beans, zucchini, cucumbers and other summer vegetables to keep the production going. Any fruit left to mature on the plant will cause flowering to slow and reduce the harvest. If you can’t keep up with your bean plants why not try pickling? Here are some Web resources that give explicit safety instructions and recipes: