Dear Rabbi Simon
Can I buy Za’atar & Sumac spices from any shop or do they need proof of rabbinical supervision (ie, hechsher)?
While it is always ideal to buy with a hechsher, as a rule, pure dried herbs and spices (whole or ground) are OK. Blends of pure spices (including with pure vegetable oil) are also acceptable. Spice and herbs salts and seasonings may contain non-kosher stearic acid and should be avoided (unless with a hechsher).
Rabbi Rashi Simon