I have Herbalism 2.
In 3 successive plantings, I have only gotten 1 herb per plot - no harvest bonuses. So, I plant 12 seeds, reap 12 seeds, and repeat. This is the same yield as I got before the skills, with the exception that I now have no failures on harvesting, sowing or watering.
The skill says, "Dedicated herbologists will appreciate Herbalism II, which further increases the likelihood of receiving little extras when harvesting, makes a triple-harvest more likely, and significantly increases the likelihood of shucking a double amount of seeds."
I am getting the little extras but triple harvests are extremely rare (in fact, I don't think I've gotten one in the 24 hours since I acquired the skill). Getting a double amount from shucking is coming a little more frequently. Is this by design or a bug? It feels like I got far more harvest bonuses from veggies gardening than from herbs. Given that herbs are not sold at vendors, it's a real chore to be able to get up enough seeds to start getting them out there to people.