Where did you "check" this? Try reading the Controlled Substances Act.

If there's an exemption in the law for decorative purposes, please cite it.

Hmm. Maybe try artistic expression covered the First Amendment. Poppy decoration is protected speech.

Just kidding ... but that's all you'll find in the law. Think i'm wrong? Go ahead. Prove me wrong with a citation to the U.S.C., CFR ... or even just one federal appellate-level court decision..