"For easier micromanagement"
It's not for easier micromanagement. You should always and only build weed plantation at the beginning of the month. That way you finish harvesting before the end of the month. The Weed Plantation is destroyed and turns back into normal Plantation. And because it's a normal plantation, you get 100k profit when new month arrives. If it was still a weed plantation, you don't get 100k from it.
People usually won't sell the weed directly, but if you do sell it, then profit depends on difficulty. On Jack Sparrow you'd only profit for 3420. That said, at the minimum you should be producing Canteen o' Wisdom with the weed.