digging up gobo

hello everyone, and thanks for reading yet another "other food talk" topic from me. there are a lot of greater burdock plants growing wild in germany, here they are known as große kletten and not eaten. my grandpa once told me the roots were edible. he said they were ok "war food", especially with a bit of rabbit, but "woody" and that he wouldn't eat them as long as he could have real potatoes. english wikipedia tells me it's the same as gobo, then goes on to say: "Plants are cultivated for their slender roots, which can grow about 1 meter long and 2 cm across. Immature flower stalks may also be harvested in late spring, before flowers appear." i didn't know you can eat the stalks. i'll try and collect some this spring. are there cultivars of this plant or is it really the same as storebought gobo? and one more question- when are the roots harvested, autumn? we've got rather heavy soil and i don't want to go digging and end up with a big basket of something useless for cooking.