I've tried everything before all the house upgrades and after, putting several family members to work watering the flowers, just one person watering etc. I've tried moving the people with the watering can in their hands and it just drops, am I missing something? How do I complete this goal?

In my experience, you must keep trying with all the family members, if possible. Eventually, one will choose the flowerpot, but it took me a very long time doing nothing but setting them to this task to complete it. Good luck!

Are you dropping them on the watering can first, or the hose? I believe if you drop them on the hose first, they will water the boxes.

Yes! Thank you, that was it, dropping them on the hose instead of the cans made him water the flower boxes.

Because this is the Plant Tycoon forum...*facepalm*

jbart321: It's an achievement known as Plant Tycoon in VF2. Not an achievement for Plant Tycoon game. I initially made that assumption as well.

Sucks when you facepalm & it turns out you had a pie in your hand.