They should simply allow it to be declared and treated as legal income, just like any other goods or services a person may render for monetary compensation. If you sell nothing, there should be no tax or law against growing and consuming and sharing with other consenting adults. If you sell more than, let's say $1k/year, it would be acceptable for them to ask you to claim it as taxable income. Perhaps there could or "should" be some kind of licensing required for "more than personal" sales...
And of course, that tends to provoke the "but everyone would just grow weed and sell it!" argument, which is farcical. They keep trying to act like it's a bad thing that people enjoy cannabis, but it isn't. They keep trying to use the addiction argument, but what if i WANT to be "addicted" to cannabis? What if i want to be free to grow and use at my own discretion? What if i plan to use a gram a day for the rest of my life? It's MY life, and *I* decide the parameters and conditions of my pursuits of happiness, and because i voluntarily adhere to the non-aggression principle, i should be completely free to do whatever i want, in accordance with that principle, and this one: "Take no liberty which impinges that of another."
Whether i choose to be a "productive citizen" or "contribute" or "participate in society," is MY choice, and is none of the government's business! (of course, they will argue that restricting my choices in order to profit from my existence IS their business... and while that may indeed describe their business, they are taking a liberty which injuriously impinges mine, without my consent, which means they are in violation of my rights! And they insist they are "justified" in arbitrarily authorizing themselves to do so!)