...a regular supply wasn't reestablished until the late 1950s. By then "King Kohl" tea had changed its name and formulation.

Yes, and it was exceptionally bad timing on the part of the "King Kohl" folks, seeing as how the late '50s was also the era of Sputnik, whose resemblance to kohlrabi sparked a huge increase in the vegetable's popularity. People were going to farmers' markets and asking farmers if they had any of "them Sputnik lookin' thangs."