Apparently it has its own holiday.

June 1 is officially "Mugicha Day" (麦茶の日), designated back in 1986 by the barley tea manufacturers' cooperative, and a MyVoice survey has it as the #1 summer drink for 40%+ of Japanese respondents, per Unseen Japan [0].

[0] https://unseen-japan.com/mugicha-japanese-barley-tea-history...