Additional information from Asahi Shinbun (4/12/2012):
The company planted the herb outdoors in MAY (not March) last year.
The president of the company said he tested the tea because TEPCO had told him he wouldn't get compensated unless he produced the result of the radiation test.
There is another company in southern Miyagi (bordering Fukushima) who makes and sells the similar product.
Browsing the popular online mall in Japan, I see the same powdered tea being sold, and one of the brands says it is made in Ibaraki Prefecture. I think they'd better test that one, too, in case.
Jiji Tsushin (4/14/2012):
Miyagi Prefecture: 20,000 Bq/kg from the herbal tea
Miyagi Prefecture announced on April 14 that 20,290 becquerels/kg of radioactive cesium was detected from the herbal tea produced by a manufacturer in Zao-machi in Miyagi Prefecture, more than 200 times the national safety limit (100 becquerels/kg).
It was 17,200 becquerels/kg according to the manufacturer's own testing. By April 14, about 40 sets of 1,100 sets of the tea already shipped had been recalled.
The herbal tea is in the powder form. About 1.5 grams of the tea powder is used to make one cup of tea, making each drink with 30 becquerels of radioactive cesium. Nothing to worry about, the prefectural government says, as if all the radioactive cesium people ingest is from this tea alone.
I suppose the prefectural government doesn't test unless they are told by the national government to test, and the national government probably didn't know about this tea. Just like they (claim they) didn't know about rice hay fed to the cows. Or leaf compost. Or shiitake cultivation substrate. Or crushed stones. Or firewood to smoke bonito. Or ....