Pollination of Squash, Melon and Cucumber Flowers
Squash, Melon and Cucumber Flowers

female flowers

It's the second week in July and your squash/melon/cucumber plants have been loaded with flowers for about two weeks but still no fruit. What's happened?

The flowers you are seeing are likely to be all male flowers. Squash, melons, and cucumbers produce male flowers first and are then followed by female flowers which often form on side or "lateral" branches. Be patient and they will appear.

"I have female flowers but they don't do anything",
"I get fruits but sometimes they're all skinny at one end and not the other" or
"they just curl-up"

A likely cause is poor pollination. Although pollination may be influenced by several factors like environment or nutrition, bees play a substantial role in all cucurbit pollination. Low populations of bees are now common in many parts of Northern America due to a parasitic mite infection which has reduced the wild populations of bees. Bees are also sensitive to many pesticides. Improper applications of pesticides can be harmful to bees. Some pesticides are more toxic than others. Care should be taken to apply pesticides after the flowers have closed (late afternoon - evening) to reduce bee exposure. For more on bees see either Pollinator's Page, Bee Pollination of Cucurbit Crops or view the world from a bee's perspective.

One can reduce pollination problems by making the pollinations themself. This is easy to do, but it requires proper identification of the gender differences. Although these pictures are of cucumber, the other members of the cucurbit family (squashes, melons, luffa, pumpkin, gourds) are very similar in their flower appearance and gender difference. One can use these as a general guide to determining sex.

male and female flowers Gender differences of cucumbers. The male flower is on the left, the female on the right. Notice the swollen "stem" at the base of flower on the right. This is the ovary which will develop into the "fruit" (cucumber). One wants to add pollen from the male, to the inside of the female flower to ensure pollination. Both flowers should be open. Pollen from the male should be visible and its parts not brown. Remove the male but not the female flowers.

cuke flowers Transferring Pollen. One can assist the transfer of pollen by removing the petals of the male (left) to form a "wand" utilizing the stem as a handle. Gently apply a liberal amount of pollen from the "wand" to the stigma of the female (yellow tip). One need not remove the female petals to do this ( removed here to show the stigma). In fact, one may want to leave them on to continue to attract pollinators. The ovary should begin to enlarge within 3-5 days.

To make your own crosses involves more effort. One must first emasculate (remove the male parts of) the female flower before the petals begin to open (depends on the crop). The stigma may not be ready yet so it may have to wait a day. Cover the exposed flower (which may look similar to the female on the right) to prevent any cross pollination from other pollen sources. For more on how to cross cucurbits see either:

Basset, Mark J. Breeding Vegetable Crops. Westport, Conn.: AVI, 1986.
Deppe, Carol. Breed Your Own Vegetable Varieties. Little, Brown and Co., Boston: 1993.

Other problems can occur after the transfer of pollen (pollination) has occurred during the period known as fertilization (not to be confused with manure or miracle grow). For more information about the fertilization problems, the pollination of vine crops or cucubits in general try these links.

Thanks to fellow grad student Dr.Alan Walters who allowed me to photograph his research plants

Cucurbit Genetics Cooperative
NCSU Cucurbits Breeding

RelativeToxicity of Pesticides to Honey Bees
(Anderson, et.al. 1971; McGregor, 1976; Wedberg and Erickson, 1986)

Highly Toxic
Dursban®, chlorpyrifos
Guthion®, azinphosmethyl
Sevin®, carbaryl
Dithane M-22®
Gramoxone®, paraquat

Moderately Toxic
Furadan®, carbofuran
Thiodan®, endosulfan

Relatively NonToxic
Dipel®, Thuricide® Bacillus thurengiensis, Bt
Arasan®, thiram
Bordeaux mixture
Bravo®, chlorothalonil
Dithane M-45®, mancozeb
Dyrene®, anilazine
Kocide®, cupric hydroxide

For a more complete listing see pages (219-221) of Lorenz, O.A. and Maynard, D.N. Knott's Handbook for Vegetable Growers: Third Edition. John Wiley and Sons, New York. 1988.