Cucurbit Sex

In the summer garden, the melons, squash, cucumbers are the lookers. They've got sexy tendrils and bright, brassy, bosomy blossoms. They're such vibrant growers that they tumble all over each other and everything else, climbing trellises, walls, the ground, into the lemon tree. Unstoppable. Funny. These plants are the whole package.

If you're as entertained by cucurbits as I am, perhaps you'd like to try your hand at saving seed of your favorite varieties.



Identifying species: If you want to save seeds from your cucumbers, melons, squash, and pumpkins, you must know what species you have growing in your yard. If, among squash, you have only a butternut (a C. moschata cultivar) and a pattypan (a C. pepo cultivar), you should be able to plant seeds from the saved fruit and expect the plants to grow true. But, if you're growing a Hubbard and a Banana squash, both C. maxima cultivars, it is likely that pollen has crossed successfully between them and the seeds will not produce an exact replica of either parent. In short, like any other genus, varieties within the same species easily cross, while those of different species only very rarely do so. So, in order to keep track of what species you have, I've written a brief description of of the more common cucurbit species below.

Cucurbita pepo: All the orange carve-able pumpkins are C. pepo, but so are zucchini and pattypan. The basic identifying key is that the stem where the plant attached to the fruit tends to be very ridged with five distinct ridges. The leaves and stems tend to be very prickly.


C. maxima: The leaves of C. maxima are among the largest and are usually an even green. The fruit-to-stem attachment on C. maxima is easiest to identify: the stem is round (not ridged), it isn't enlarged against the fruit, and it is less strong. C. maxima can be just about any color, but they aren't usually bright. In other words, an orange C. maxima will be a soft, rusty pinkish orange instead of a Halloween C. pepo orange. They can be steely blue, pink, deep green, etc. In the maxima species, I am growing Uncle David's Dakota Dessert and an unidentified variety that I brought back from Argentina.



C. mixta: The fruit of mixtas (aka cushaws) usually aren't terribly tasty, but they have huge seeds with distinct, silvery rims around the seeds. These varieties are often grown for their seed alone. The fruits looks similar to washed out moschatas. I don't grow any mixtas.

C. moschata: The leaves on C. moschata plants often have silvery spots. Also, their fuzz usually is softer and less prickly than either pepo or moschata. The place where the stem meets the fruit is smooth and has five points that flare out against the fruit. The fruits are most often pinky-tan colored, a la its most famous cultivar, Butternut. However, moschata fruits can occasionally be dark green or green and ivory mottled. I grow Seminole, a historic moschata.



Pop quiz: Which two species are in this picture below? Which is which?


Cucumis cucumis: Cucumber! Easy to identify. This year, I'm growing Poona Kheera.

Cucumis melo: All melons (except watermelon) and a couple "cucumbers" (Armenian cucumber and Bari cucumber). This year, I'm growing an old favorite, Boule D'Or, two new-to-me varieties, Eden's Gem and Petit Gris de Rennes, and of course, Armenian cucumber.



Citrullus lanatus: Watermelon! Once again, easy to ID. This year, I'm growing Orangeglo.

Preventing cross pollination: The easiest way to prevent cross pollination is to grow only one of each species. While there are cases of species crossing (the mules of the cucurbit world), those are the exception rather than the rule. If you're like me, it is really hard to contain yourself to just one variety of each species. I know that I will never have a garden with just one kind of melon in it. One kind of melon! That's practically starvation.

If you choose to grow multiple varieties within a species, the most practical means of preventing cross-pollination is mechanical isolation and hand pollination. To do this, walk out to your garden and look at your flowers. Make sure you can identify male and female flowers.

This is a male squash flower. It has no immature fruit at its base, but it does have a pollen-rich anther in the center.


This is a female squash flower. It has a large, irregularly shaped stigma and an immature fruit at its base.


This is a male melon flower; melons, watermelons, and cucumbers have nearly identical flowers. The anthers are low and tucked into the base of the flower.



This is a female melon flower. It has a stigma that can easily collect pollen off the insect pollinators.



Now that you know what you're looking for, find several just-about-to-open female and male flowers of the variety you want to keep from crossing with any other variety. If you can, choose flowers from more than one plant in the same variety because that will help keep a healthy gene pool in your resulting seeds. Tape the flowers shut.



The next morning, when the flowers would open with the sun, cut the male flower off the plant, carefully remove the tape from it, and gently tear the petals off, leaving the anthers exposed. Remove the tape from the female flower, coax the petals open, and insert the male flower into the female flower, shoving the anthers up to the stigma. After you see the stain of pollen on the stigma, cover the female flower with something to protect it from any other creature that may want to crawl around in it. I use poly mesh bags, the kind that some people use for wedding favors.


Once you're sure the young fruit is growing (see below), identify it with a ribbon or stretchy tree tape to remind yourself later that this is a fruit with pure seed.

Protecting fruit: Not every fruit will "take," no matter how carefully you work to pollinate the female flowers. It's easy to determine which of the female flowers are truly pollinated, because they'll take off growing almost immediately. If you have lots of pillbugs and similar in your yard, as I do, protect the growing fruit by placing a plate, brick, or other object underneath it, keeping it off the soil.


This is a female fruit that the plant will abort. Notice that it is yellowing towards the blossom end. The stem is also anemic, telling me that this fruit won't develop further.


Saving seeds: Now that you've worked hard to protect your varieties from cross-pollinating, it is important that you save seeds from mature fruit. It is easy to tell when seeds in a melon or watermelon are mature, because they're ready when the fruits are ready to eat. However, the seeds in a zucchini that you'd eat aren't ready to save; the fruit must stay on the vine until the fruit is bloated, like an oddly shaped pumpkin, and hard, so hard that you can't pierce the skin with your fingernail.

And cucumbers that are ready to collect seed from don't even look like cucumbers anymore. Here is a Poona Kheera cucumber that still isn't ready to harvest for seed; the skin needs to toughen more, to feel like a ripe melon, before I remove it from the vine. Sometimes cucumbers will even split open and reveal their mature seeds.


When you do remove the seeds from a fruit you've saved for seed, scoop the seeds out into a colander, give them a quick rinse, then spread them on a cookie sheet (if you like, you can line it with parchment, but that really isn't necessary) to dry thoroughly. Once completely dry (and I mean completely, totally, very, very dry), store in a cool, dark place.

Cucurbit love. I've got it bad. Maybe you do too?