To sell packed nature weed you have to consider and do some things beforehand. You have to buy seeds to grow and find a safe spot so your weed doesn't get destroyed by others. It definitely takes more time than usual farming routes because it's a passive way to farm. Nevertheless, you need to water your plant, otherwise it will die. More to that in detail down below.
Get started
The first step is to visit the "botany store" between Laruns and Levie. In the House you will find a NPC who sells you seeds for your nature weed.