The question.
Recall Post G22-013, where I proposed to bypass last year’s troubles with cucumber beetles and squash vine borer by growing parthenocarpic varieties of both plants. A parthenocarpic plant is one that produces fruit without fertilization, that is, without pollination. No bees needed, which means I can grow them inside an insect-proof enclosure, excluding the bees along with the pests.
The resulting fruits are sterile and lack fully-developed seeds.
I have to admit, as I ordered up a few packs of seeds for various parthenocarpic cucumbers and squash, I did have this nagging little question: How do they produce viable seeds from parthenocarpic plants? Isn’t “seedless cucumber seeds” an oxymoron?
I stifled that question and ordered the seeds anyway. The seeds I bought were offered by a presumably reputable seed merchant. And I know that greenhouse-based farms produce plenty of produce from parthenocarpic varieties. Didn’t seem like much of a risk.
That said, buying seeds for seedless cucumbers does seem like a bit of a Catch-22. Or maybe a chicken and egg problem. Perhaps my local nursery stocks the seedless cucumber seeds right next to the dehydrated water.
At the time of purchase, I noted a seemingly unusual percentage of purchasers’ comments complaining of low or no germination rate. But you see comments like that on the sites of any seed vendor. I chalked up the squawking to the relatively high cost per seed. These parthenocarpic varieties seem to sell for anywhere between 25 cents and 50 cents per seed. A poor germination rate is not much different from mulching your plants with ground-up dollar bills.
And now, of the 20 seeds planted (five different varieties, three cucumber, two squash), in peat pellets, exactly four seeds appear to have sprouted. These are from two cucumber varieties. All the rest of my new whiz-bang parthenocarpic seeds appear to be duds.
But is that normal? And is it true that they failed to sprout, or is there some other explanation? Because if that’s really the germination rate, I paid somewhere around $1.75 per viable seed. For cucumbers and squash. Which feels more akin to mulching your plants with $20 bills.
So that gets back to the main question of this post: How, exactly, do seed vendors produce seeds for parthenocarpic varieties? (Or, more simply, where do seedless cucumber seeds come from?) And is there usually a low germination rate for parthenocarpic varieties?
The answers.
As it turns out, there are several ways in which you can get viable seeds for “seedless” parthenocarpic plants. But as far as I can tell, the most common parthenocarpic varieties are F1 (first-generation) hybrids. So, by and large, you don’t get seedless cucumber seeds from seedless cucumbers. You manufacture them by crossing two seeded varieties that generate the parthenocarpic (seedless) first-generation hybrid offspring.
Of the five varieties I planted, four of the five ( Diva Cucumber, Sweet Success Cucumber, Easy Pick Gold II squash, and Golden Glory squash) are either explicitly marketed as F1 hybrids, or simply as hybrids.
For those, there’s no fundamental reason they would have any lower germination rate than any other F1 hybrid. These same varieties are planted by commercial farmers growing produce in greenhouses and poly tunnels. Presumably, they wouldn’t put up with extremely low germination rates.
The sole exception to the F1 rule is Little Leaf cucumber. As it turns out, that is an open-pollinated variety, not a hybrid. But that’s also a gynoecious variety — that is, it produces all (or nearly all) female flowers. Thus, you can get a Little Leaf cucumber with seeds, in the rare event that a male flower is produced that fertilizes one of the many female flowers.
So the upshot is that of the five seedless varieties I’ve chosen, four are F1 (first-generation) hybrids, so the seeds for them are actually produced by crossing two non-parthenocarpic varieties. I don’t think they’ll produce seeds under any circumstances. And the last one is seedless, but only because the plants are rarely fertilized owing to its gynoecious nature. It’ll produce either seeded or seedless cucumbers, depending.
Now that I know how this works, I’ve done what I should have done from the start, and dissected the peat pellets that I planted these in. Mystery solved: There are no seeds inside. Plausibly, some birds came by and pecked the seeds out while I had these sitting outside. So all I need to do is replant, and be a bit more careful, and I should be able to proceed according to plan.
I’ll report back on the actual (bird-free) germination rate in a couple of weeks.
