GoodAndEvilbeta

Herbs, like allotments and hops and assuming they have not died from disease, work as follows:
You start with 3 lives.
Each time you harvest a crop, you roll the dice.
If you roll successfully, you maintain your lives count.
If you rolled unsuccessfully, you lose a life.
You will repeat from Step 2 until you have lost all 3 lives and then the patch becomes empty.
At the minimum, the amount of items you will harvest will be equal to the amount of lives you started. If you use compost, you start with 4 lives instead. If you use supercompost, you start with 5 lives instead. Secateurs make you more likely to roll successfully by 10%, so you are statistically more likely to get more items, but not guaranteed.
Your Farming level will affect the likeliness of succeeding each time the dice rolls.

According to Mod Kieren, if you farm higher level herbs, you are less likely to lose a life, compared to farming lower level herbs. That being said, this difference will become much more minor as your farming level increases. At level 99, all herbs will have the same likeliness of succeeding.

In theory, if you rolled successfully every time, you'd get an infinite number of items.