My fairy Sim needed crystal flowers to make some chips for robots so I grew a garden of them on the roof. Here are my discoveries as I played with this concept.
1. Like any other garden plant they need to be "tended", "watered", "weeded and "harvested". Using "Tend Garden" command also triggers charging if they have once been charged.
2. There are 4 emotions that can be charged, Kindness, Humor, Love and Rage. Each has it's own color, green for kindness, blue for humor, pink for love and orange for rage. They start out as pastel shades but deepen with the second charging.
3. You cannot multiple charge at once. No charge with kindness on a plant and then going immediately after to do it again. However, if you wait a bit, or charge another plant you can go back and charge again.
4. The charges give you the following:
1st. charge gives you 27% full
2nd charge gives you 54% full
3rd charge gives you 81% full
4th charge gives you 100%
5. It takes 8 Sim seconds to charge each flower during which time you will hear different sound effects, color swirls and silly actions. The one that amused me the most is the one leg up behind during the love charge.
6. Fairies can bloom these plants like any other so you can repeatedly harvest them. Charges weaken after the plants are harvested or if they are ignored for awhile so you have to constantly be tending them. Fortunately, the tend plant command recharges them.
7. Like any other plant their quality ranges from nice to perfect. It does not seem to make a difference when making chips what the quality of the flower is.
8. They can be purchased at the Bot Emporium but cannot be consigned there.
9. To change the kind of charge you have to select "Neutralize" first and then charge with a different emotion.
I tried just charging the ones in the wild, and they charge just like the others, but since my Sim was busy doing other things I never got back to do more than one charge and don't know if the charges held.