So this system is pretty simple and you can use it for as many plants as you want to be able to plant. You need a few switches for each plant, as well as a variable and a common event. The three types of seeds/herbs I used for this tutorial were Flux, Tuneq, and Poe. For the info you need below, I'll be using Flux as an example. There's also 3 different spots in the tutorial for planting seeds, so that's why each thing you need is numbered.
And that's for each switch (planted and grown), variable, and common event.
So the planting events are pretty simple. Use Conditional Branches to check if the player has the item in their inventory, and if they do, allow them to plant the seed. Turn on the Planted switch and have the Planted Seed icon pop up on the map. After the switch is turned on, have the common event be activated. In the common event create a loop. Have it wait for X amount of time (40 in my example) add 1 to your variable (in this case, Flux 1) afterwards, until it equals to a certain amount (in this case, 10). Have a conditional branch that says if the variable equals 10, it turns on the Flux Grown switch and turns off the Planted switch (in that order) and then breaks the loop. Now that the common event is turned off, the original planting spot should now have the Grown Plant icon shown, and allow the player to harvest the herbs. If you added the Herb Chance variable, have it randomize between a set of numbers (in this case 1 - 3) and set the "Give Item" amount to that variable. This allows the player to get a random chance to harvest extra herbs.
And that's it. If you guys need pictures let me know, but it's a pretty simple system. I included a demo below, it has comments in the events explaining them again just in case you need them.
If you have any questions/comments or need help, please post below .