I disagree with the low probability.
For wild berries, be they raspberries, black berries or wild blueberries ( not the domesticated shrubs you see nowadays ), they can be invasive if left to themselves. They can survive in low water areas, as well as very wet.
In FF all of the herbs you can find have been grouped together under a single large “herb” resource. There are herbs for every climate and growing condition. Herbs that need arid land, others that prefer sandy and good drainage, some are bog plants, or want for denser clay soil. Since all of the herbs are classified simply as “herbs”, it won’t matter where exactly you place them. My point is that if the herbs are growing naturally in your map, then in general they will thrive pretty much anywhere in that map.
The above is why I do not agree that there needs to be a low probability. I do like the idea of it being part of an upgrade. Or maybe tie the cultivation of berries in with the arborist, and the cultivation of herbs in with the apothecary shops, since most herbs have some medicinal value as well.