Green’s Dictionary of Slang

potted bush n.

[SE potted, confined in a small space + bush n.¹ (5a)]

(drugs) hashish.

1959		J.E. Schmidt Narcotics Lingo and Lore.
1975		Hardy & Cull Drug Lang. and Lore.
2001		ONDCP Street Terms 17: Potten [sic] bush — Marijuana.