The same thing applies to me too! As far as I know /herbalism command states that you can get herbalism exp when you break blocks such as wheat, pumpkin, carrots, potatoes, basically all types of crops.
I made a huge giant wheat farm (2x2 plots) and I haven't gained a single herbalism exp. The only way I can get herbalism exp is as follows:
1. Breaking limited crops such as pumpkin, melon, sugarcane, and cocoa
2. Breaking random flowers or grass in plains
3. Redeeming points from voting or artifacts
4. Party mcmmo exp grinding herbalism
Aside from that there are nothing else I can do to gain herbalism. I also reported it to Sir Trickster_ regarding this issue yesterday.
So, all of this is true. However, I stumbled upon something interesting. Wheat that is grown from the natural world generation (not player grown) still grants herbalism xp. The same goes for carrots and potatoes.
I remember this was once an issue previously, but not sure if it was fixed as I stopped playing during the time after. But in regards to mcmmo in general, using bonemeal on a plant will not yield mcmmo (I think that is what DeserFox02 is referring to). For anyone having the issue, are you using bonemeal? And if so, try planting and harvesting without bonemeal, and let us know if you still have the problem?
Wenzer, I was not referring to bonemeal at all. I meant crops that are there from the start of the world, meaning that they were generated when the world was created. Any of these player-placed crops will not yield exp. Bonemealed crops will never yield exp (with watermelons and pumpkins being a special case).