The model in my mind of an edible dahlia seeds itself abundantly, and grows tenaciously; tubers just spontaneously generate over summer for fall harvest; the tubers you don’t care to dig freeze, so never become a perennial problem. I really do think this is a realistic vision, but it might take a little species trials to find the right one.
Cultivariable has done some excellent work gathering a collection of dahlias they consider edible, and are harvesting the seed for further selection. I read through an excerpt of his very informative book on his website which I subsequently grabbed a copy of (link below if you’d like to to check it out. It covers far more than dahlias) but saw no mention of self seeding.
He is already sold out of this year’s available tuber and seed stock anyway, so I looked deeper.
The species he raises are Dahlia pinnata and coccinea. Pinnata is the species most often cited as edible, and actually grows wild in the lower southeast US according to the USDA Plant Database -Mississippi and North Carolina in particular.
This was helpful when looking at my next best option -“Bishop’s Children” mix. I’d seen it many times in seed catalogs because it’s commonly grown as an annual from seed. It’s the progeny of “Bishop of Llandaff” -hence the name, and is believed to be cross between pinnata and coccinea.
This background information seems to originate from a single article profusely circulated and cited in Wikipedia articles. But the characteristics I see in pictures agree with the story. I think it’s worth believing. The seed is widely available so why not try them anyway?
The plan is to get the seed and sow some for carefully potting up and transplanting, the rest just spread around in opportune patches in the food forest to see how easily they take. Assuming they form plenty of tubers (most dahlias are day length sensitive, some forming only small, and very few, tubers before frost) and assuming they taste good, they may become a prominent citizen of Mortal Tree, and perhaps find their way into my client’s gardens as delicious, productive little gem mines.
Above: The same heirloom dahlia in the opening photo, now harvested, with tuber harvest laid on the aerial parts which are now mulch.
The book I mentioned: The Cultivariable Growing Guide: Sixteen Rare Vegetables for the Pacific Northwest
Mortal Tree 