Courtesy of John S., Blue RIbbon Eggs, Franklin NC
Your complaint about low yields is a common one for 'Potatoes in Bags' (or barrels or any other elevated growing system). My theory is that potatoes are a natural mountain crop evolving in very cool soils at high elevation, and we need to mimic that condition, or at least come close. Additionally, when you elevate your growing platform you inevitably raise the soil temperature in the daytime and create greater cooling at night. As a result there are greater temperature swings in a 24 hour period as well as over a season. It appears to me that potatoes need a very stable temperature profile with little variation in a 24 hour period and over a season to make well formed tubers. That means "In the Ground".
I'm not sure that "I saved on labor' is really true given the assumed extra attention that type of growing would entail. I grew four 60' rows by planting 60 or so pounds of seed. In the first two rows I harvested 250 pounds of potatoes and still have two more rows to harvest.
Planting is work. After tilling I dug Four 60' trenches 12"x12" with a grub hoe. Took days to dig. Next season I'll just till and furrow.
My beloved bride, The Smoky Mountain Queen, who was raised in the old ways (wood stove, grow your own food, no indoor plumbing, medicine from weeds by the creek) never refers to "Harvesting potatoes". She calls in "Grubbin' Tatters". And that's what it is. On your hands and knees, digging with your bare hands down the row, emptying the trench you dug four months ago and tossing the 'tatters' off to the side to pick up and store. Not really a big deal, but do this before you get your nails done.
On the other hand, I figure I've spent a total of 5 or 6 days of labor(planting in a trench
and harvest-or 'grubbin'-) and 4 months of benign neglect as Mother Nature did her thing.
And I got a ten fold return on my investment of seed-down right biblical.
If I figure that I spend 25 hours planting and harvesting those first two rows (and virtually no
maintenance time involved at all) that's 12.5 minutes of labor per foot of row and I got over 2 pounds per foot so that's ten pounds per hour of labor.
I think Gro-bags are cool as can be, but I'd use'm for tomatoes and peppers.