As far as I can tell, the simple rules for potions and herbalism were removed from the core rules between 4th and 5th edition. Maybe I'm blind.... Where might I find rules for either, especially if there are new detailed rules?
AFAIK you are correct.
Herbalism as a substitute for Medicine is in Art & Academe.
Mythic Herbalism is in both HoH:S Ex Misc (Pharmacopeians) and in the Learned Magician section of Hedge Magic and is particularly relevant to Cunning Folk.
Rules for Hermetic integration for rapid creation of single shot items (ie potions) are presented at the end of the latter chapter.
regards,
Lachie
(I thought you were specifically referring to herbalism - see below)
Really?!? There's no rules for potions except as hedge magic?!? Wow. From a history of magic standpoint, that strikes me as a really large omission. I'm quite surprised.
Thanks for the info!
Charged items can be potions (ArM5, top of p97). Folk Witches in HMRE also use them.
As other have said, Herbalism is in A&A p55. Mythic Herbalism is both in HMRE p 81 and HoH:S p125. I never managed to understand how they differ in power.
I'd send you to Arts and Academy, chapter 5, specifically the rules for Phamaceutical Theriacs. Not really as powerful as the old Herbalism rules, but functional.
For hermetics potions are charged items. Mythic herbalism is one of the coolest abilities in the whole game, though, so I would suggest you take a deep look at it. 
Tugdual, the rules in both HOH:S and TMRE are the same.
Xavi
Less concisely: Hermetic charged items can take the form of potions (without the underlying mechanics changing).
Folk Witches also use potions, but with rules that differ from those of Hermetic potions. In a nutshell, potions are one way in which they can produce effects through their supernatural abilities. For example, they can create a Love potion that essentially Curses the drinker with a strong emotion, or a Second Sight potion that allow the drinker to see things as if he had Second Sight.
We always called the later "the Hofmann potion" or "Lucy's potion".
Xavi
Hmm?
en.wikipedia.org/wiki/Lysergic_acid_diethylamide
Lucy
Sky
Diamonds
Basically it is an acid trip to see the world in Second Sight if you do not have the ability as default. Quite easy, really
I kind of assumed it was, but in this case I meant between Herbalism and Mythic Herbalism. 
I was referring to herbalism in the main rather than Hermetic magic. There are no explicit rules for potions like previous editions - they are treated as charged devices in general and could have more than one charge / draught I suppose but the flavor text and interaction with herbalism has been removed in ArM5.
I suppose a Mystery that allowed substitution of Herbalism for Philosophae in the Lab Total might regain some of the flavor but I'm not sure if that's the thrust of your question. The Vulgar Alchemy Mystery Virtue IIRC might be used to gain new S&M bonuses with a herbalist theme also but Herbalism in ArM5 is now just a variant of Medicine.
I can't remember if Herbalism allows the production of Theriacs per the Art & Academe Natural Experimentation rules.
I see no reason why it shouldn't though.
Lachie
We've been using the following Shape & Material bonus for so long that I'd forgotten it was unofficial:
Any liquid: +5 affect drinker.
You know reading through Cradle and Crescent I notice a number of reductions and potions and such that uses many different ingredients and preparation methods which then are used to give minor or major virtues or flaws.
While it lacks a lot as far as ability rules and such it certainly is very flavorful and can be used at least for the story aspect of herbalism and potion making.
Thanks for all the info!
A) Looking at the Mythic Herbalism / Root Cutter virtues in HoH:S -- does anyone see any reason why the Root Cutter virtue could not be made available to any player? I know it's presented as a Secret known to the Pharmacopaeons only, but it fits the player's character (who is not a Pharmac), and I'm leaning toward allowing him to choose it... just wanted to see if anyone thought it might unbalance things.
B) To my knowledge, there is no way to make a permanent "Healing Potion" -- Duplicating the effects of "Chirurgeon's Healing Touch" (heal one body level), because it is a Ritual spell. As I read the rules, you can make poultices, theriacs, etc., but these expire after a while because the ingrediants spoil. All of this makes sense to me, but I just want to make sure that with the rules as written, I'm not missing anything.
My ex Misc Daughter of Circe (focusing in transformation and in herbalism/potions) took Root Cutter, because it fit my idea of what her tradition does, and as long as there are magical plants and herbs that she can gather and prepare beforehand, it seems to have worked so far.
But yeah, all in all I agree that they do seem to have nerfed Herbalism when they went from 4th to 5th edition. And trying to cobble together all the pieces from hither and yon to rebuild what Herbalism used to be gets kind of annoying sometimes.
AFAIK, only Witches (HMRE) have true healing and no others offer a path for hermetic integration.
Yup, ritual. In fact it is a rather BAD ruitual as it is in 5th edition. When it used to heal a body level it was a useful spell, but right now you'd better invest your lab total in manufacturing potions that provide a year duration bonuses to recovery. Get yourself a +12 or +21 bonus to recovery and you are way better than with CHT. it is unlikely that you get bad from your wounds/diseases unless you botch.
If you have mythic herbalism you can have this same bonus generated by the dozens in a season. It is difficulty 15 to generate a mythic herbalism *4 bonus to recovery. That is a +20 easily. In fact mythic herbalism is way more efficient than hermetic magic at healing and poisoning. And it does not require vis.
Cheers,
Xavi
Kind of a newbie question (and slightly off-topic), but... is this possible with vanilla magi? Isn't an effect with Year duration always a ritual and thus impossible to put into an item?
True, my bad. I meant season. Since season is a non standard hermetic duration you need to apply an extra magnitude to it (so it would be +5 magnitudes, year +1 for non standard). it has the advantage that it does not require vis.
So it is Base +6 magnitudes for a bonus that applies during the whole season at touch range. It warps you slightly, but it is easy to get a +12 bonus for all recovery rolls with a CrCo35 spell. That is generally better than curing straight a light wound.
Mythic Herbalism is much more efficient at achieving the same bonus easily. It is difficulty 12 to brew a potion that gives you MH*3 in recovery bonus. That is easily a +15 for a starting character that invested some in MH. His total of Int+MH (say, healing effects specialty) + aura of 3 is easily on the range of 2+6+3+ D10. total of 11+ D10, basically. +1 difficulty for additional potion. It would take him 4 days to brew that potion batch. Make him brew potions for 3 weeks trying to pull 3 potions per batch (difficulty 14, so he needs to roll a 3+) and you get a total of 12-15 potions that grant a +18 to all recovery rolls for less than a month's work. Not bad for your local healer. And this is way less than a specialized character (intelligence 2, aura 3, MH 5 with healijg specialty). hermetic magic can do almost everything, btu other people just can do some of that stuff better
As a side note I find the lack of a Season duration weird, since hermetic magi use seasons to keep track of most of their stuff.
Cheers,
Xavi