Edit 7/29/2022: Read post G22-050 first.
Theological and horticultural background
A parthenocarpic plant is one that produces fruit without fertilization, that is, without pollination. The resulting fruits are sterile and lack fully-developed seeds.
Without getting into the deeper theological aspects, the word derives from the Greek “parthenos”, meaning virgin. And “carp”, meaning to complain. Thus, the Parthenon is a temple to Athena, who was virgin who had few complaints.
(Technically, carp means seed. So parthenocarp means “virgin seed”. I like my version better.)
Of course, now that you know the word, examples crop up everywhere. The banana is almost surely the most familiar example of a parthenocarpic fruit. If you’ve ever wondered why bananas are seedless, now you know. It’s due to their parthenocarpic nature.
Every parthenocarpic fruit is more-or-less seedless, but not every seedless fruit is parthenocarpic. Some still require fertilization, they just don’t (or rarely) produce fully mature seeds. Seedless watermelons fall into that category. Unlike true parthenocarpic plants, seedless watermelons must be pollinated to bear fruit. The term of art there is “stenospermocarpic”, which seems to be Greek for narrow fertilized seeds.
This is also not to be confused with plants that require pollination, but not pollinators. Those include plants that are “wind pollinated” (like most cereal grains), and plants that may be “self-pollinating” due to perfect flowers containing both male and female parts, so that simply shaking the flower may sometimes pollinate it. (This is the source of the electric toothbrush hack for ensuring good tomato pollination.)
Parthenocarpic cucumbers and summer squash.
Greenhouse and poly-tunnel farmers provide the commercial demand for parthenocarpic varieties of common garden plants such as cucumbers and squash. In those enclosed environments, without bees, those crops would otherwise have to be pollinated by hand. That’s an obviously labor-intensive step, and may be a practical impossibility for crops grown under low “hoop house” type row covers.
Several different varieties of parthenocarpic cucumbers and squash are available to the U.S. home gardener. I’ve been compiling a list, but I’ve limited it to the small subset of fruits that appear more-or-less identical to their seeded, pollination-requiring cousins. The subset of interest to me includes:
Cucumbers: H-19 Little Leaf, Corintino, Dive, Excelsior, Piccolino, Quirk
Squash: Venus, Part(h)enon, Burpee’s Sure Thing, Defender, Duntoo, Dunja, Cavili, Golden Glory.
(Parthenon or Partenon, sure. But Venus? Singularly inappropriate.)
As far as I can tell, these are exclusively F1 (first-generation) hybrids. (Because, seedless, right?) So if you will only grown heirloom plants, or those from which seeds can be saved, this is not for you.
To determine which varieties to grow I will apply the Tomato Paralysis cure from Post G22-001. List in hand, I’ll cruise the seed racks at my local garden center and grow whichever of those they carry locally.
As a bonus, I can have my very own guilt-free arena of death.
I ended up here because I had such a dismal time trying to grow cucumbers and summer squash for the last couple of years.
The squash vine borer is present in this area (Virginia Zone 7) for a couple of months. That is, more-or-less for the entire squash growing season. If you restrict yourself to relatively short-lived pesticides (I used spinosad), controlling it requires careful spraying at five-to-seven day intervals. See Post #G27, A Treatise on the Squash Vine Borer.
The cucumber beetle was essentially absent from my first year of gardening, and I had a bounteous crop of cukes. But by my second year I had built up an unstoppable population of them, and got almost no cucumbers whatsoever. I never found a way to control the cucumber beetle that a) worked and b) was acceptable to me, in terms of environmental impact.
The damned things are like vampires: All it takes is one bite. Cucumber beetles spread bacterial wilt. So it’s not the actual leaf and blossom damage from their feeding that matters. It’s that any feeding at all infects the plant and kills it. As far as I can tell, a) once bacterial wilt starts, it’s just a short while until the entire cucumber plant is dead, and b) “wilt-resistant” cucumber varieties aren’t, they end up just as dead as non-resistant varieties.
But if I don’t need pollinators, I can grow summer squash and cucumbers under insect netting/row cover. In theory, if I can sterilize the soil under the plants (with a neem oil soil drench, perhaps), and keep a bug-proof enclosure over the plants, I can physically prevent those pests from reaching the plants. And yet have a crop, because barring the bees entry does these plants no harm.
I’ve been hesitant to try this. Not just because it seems like a lot of work to set up, and a lot of hassle to maintain. But because of the “vampire” nature of cucumber beetles. It’s not their feeding that matters directly, it’s the disease they carry. If a single beetle breaches the defensive perimeter, it’s game over for the cucumbers. Do I really think I can (e.g.) lift the cover off to pick the ripe fruit and set it back again without letting in a single cucumber beetle?
It seemed to be a fairly non-robust setup. I understand that insect netting can greatly reduce insect damage. But because of the nature of the beast — bacterial wilt — I really need to eliminate it entirely. If the endpoint is going to be a bed of deceased cucumber plants, I know ways to achieve that with a lot less effort.
But if the bees and butterflies can’t get in … then nothing bars me from making that enclosed garden bed an arena of death. All of those highly-effective (i.e., deadly) pesticides that I normally won’t touch due to bee toxicity are now back on the table. Subject to some constraints, nothing need stop me from hosing the bed down with (e.g.) pyrethrins on a regular basis (subject to controlling runoff). This means I can install a secondary, chemical line of defense beneath the primary (physical) barrier. If need be.
I’m looking for parthenocarpic, not carcinogenic. So it’s not like any pesticide is fair game. But cheap, short-lived and effective organics like pyrethrins would seem to be plausible. Once I screen in the bed, I no longer have to worry about killing off my local bees and butterflies. More-or-less any bug that gets through the outer defenses is fair game.
Conclusion
Anything worth doing is worth over-doing. Given how much hassle it’s likely to be to do this at all, I think I’ll go for more, rather than less.
My plan is to dedicate one entire raised bed to parthenocarpic cucumbers and squash. Roughly 4′ x 16′ or so.
Plausibly the major expense will be for the requisite statue of Athena, so that I may dedicate my parthenocarpic garden appropriately. And some large-economy-sized Bucket-o’-Death, to ensure that any bug making it past the cover will die ASAP.
Otherwise, for me, this requires no investment in materials. I already own a more-than-lifetime supply of thin floating row cover. As well as a pile of loose PVC pipe and fittings, which is to adults what Tinker-Toys are to kids.
A year ago, I didn’t even know that such a thing as parthenocarpic squash existed. This year, I’m going to grow a bed of it. I’ll let you know how it turns out.
