I used to get results like that, but then the critters got to the sunflowers and would chomp them down before they ever had a chance to get started. Then I stopped trying sunflowers for several years and now my mammoth sunflowers turned out to be dwarf sunflowers [laugh]
I'm disappointed in my sunflowers - the seed packet said "Mammoth" sunflowers and they are supposed to be 12'-15' high -- pictured below is the result -- did I get ripped off or is my soil just crappy ?
No idea regarding the variety - we bought the plugs from a local garden center and they were labeled "pickling cukes".
They still taste great despite their large size, so I don't think we let them go too long or they'd taste woody. I don't see something of this size fitting in a mason jar for...