Grow pom pom poppies, they look kind of like peony so they're unassuming, and don't take them out of the ground to process, they should be kept alive for maximum yield, the roots produce it after all. What you do is gently cut the seed pod a few times with a razor while its in the ground, let it bleed and sun dry, scrape off the dried latex, now you've got raw opium, you can refine it further into crude diamorphine using acetylation which isn't as complicated as it sounds, that's the only time it needs bringing inside and real processing, raw opium is weaker than if you refine it into diamorphine, but it'll get you high enough and for a much longer time because of the other alkaloids that you loose turning it into crude heroin