Herbalism and Potion-Making in Dungeons and Dragons

One of my players, a cleric, insists on being able to pick flowers and herbs along their journey to use in a recipe to make healing potions. The DM Guide is pretty clear that making healing potions costs 25 GP and 8 hours per day, a minimum of two days depending on the rarity of the healing potion (DMG ch6), but it doesn't go into the specifics of what this gold is supposed to be spent on. I run a game that is mildly homebrew (in that it's my own story with a few of my own non-official elements) but is careful to follow as close to the official rules as possible. I also like to craft stories that are similar enough to reality that they can somehow make sense even if they're magical. So I looked into how people in Days of Yore™ healed their wounds and learned all about poultices.

A poultice is, quite simply, a mound of ground up herbs and/or flowers or roots that you place on the wound and hold in place with a bandage. It has chemical properties that help the wound heal faster. There are specific herbs you can use for a poultice, so I wrote them all down and pretty much just made up how rare each one was in my world. So how do you go from a real-life-inspired poultice to a magical potion? Add holy water! Soak the poultice in simmering holy water for 8 hours while performing a ritual, put the mixture in a cheesecloth, and squeeze out the potion into a bottle. Depending on the rarity of the herb used for the poultice, this can be repeated with a new vial of holy water daily until the poultice is spent.

What makes this system work so well is that it works out to cost exactly how much gold and time the DMG says potions take to make. Because holy water costs 25 GP per vial. And, of course, if the character is a cleric or paladin they can make their own holy water, too... Provided they have 25 GP-worth of powdered silver. And, I mean, they can grind up their own silver into powder if they really want, but at that point, I would just buy the damn potion from the magic shop.

Here's the recipe exactly as I wrote it down for my player:
--Poultice:
  • Gather Dandelion Leaves (Common), Chickweed Leaves and Stems (Uncommon) Plantain Leaves (Rare), Calendula Flower Petals (Very rare), or Burdock Root (Legendary).
  • Chop up the herbs and grind in a mortar and pestle found in herbalism kit.
  • This turns the herbs into a sort of paste as the moisture of the plant releases during grinding.
--Holy Water
  • A cleric or paladin may create holy water by performing a special ritual. The ritual takes 1 hour to perform, uses 25 GP worth of powdered silver, and requires the caster to expend a 1st-level spell slot.
  • A blacksmith may grind silver that you provide into a powder for 10 GP or a favor depending on persuasion.
  • You may also buy Holy Water from a city cleric for 25 GP.
Mix the holy water with the poultice. Set over a low flame and let simmer for 8 hours. While simmering, say a ritualistic prayer to the god of your choice. Poultice/holy water mixture will start to glow red as you gain favor with your god. At the end of the 8-hour simmer, pour the mixture into cheesecloth. Squeeze potion out of the cheesecloth into a vial or bottle via a funnel.

Repeat the following day with a new vial of holy water until the poultice is spent. How long it takes for the poultice to be spent depends on the herb's rarity. Common: 2 days, Uncommon: 10 days, Rare: 100 days, Very Rare: 1,000 days, Legendary: 10,000 days.


NOTES:

Letting the poultice sit for 16 hours allows it to decompress so that another round of Holy Water can saturate it again.

If the used poultice is left out for more than a day it will dry out and become unusable.

If you stop making a potion of healing before it is finished, it will have that percentage effectiveness. For example, if you stop making a common Potion of Healing after 1 day, because it takes 2 days to make it, the potion will have 50% effectiveness and the healing taken from it must be halved. If you stop making a Potion of Greater Healing after 1 day, because it takes 10 days to finish, the potion will have 10% effectiveness and the healing taken from it must be subtracted by 90%.
All that was missing then was a system by which to find and gather the appropriate herbs. This is where I'm very open to playing around with the rules because I'm definitely not a statistician and this definitely hasn't been play-tested yet. Here are the notes I made for  that:

Finding herbs:

DM rolls a d20 to make an Availability Roll. Available herbs stack (If you roll high enough to make rare herbs available, you will also make uncommon and common herbs available).

Climate bonus: -20 for any body of water, -10 for desert, -5 for cave, +0 for open field, +5 for farmland, +10 for forest or wetland

  • 1-7: Nothing
  • 8-12: Dandelions (Common)
  • 13-16: Chickweed (Uncommon)
  • 17-19: Plantain (Rare)
  • 20-21: Calendula (Very Rare)
  • 22+: Burdock (Legendary)

The character must roll WIS (Perception) or INT (Nature) (add proficiency bonus with herbalism kit) to see what is found according to the above table. If this roll is higher than Availability Roll, those rarer herbs are still not found even though they would otherwise be able to find them. They just aren't there.

So I made this system because my player was a little confused about how to use the herbalism kit to make potions, and, to be honest, I was, too. Of course, there is no provision for this in the official rules, but, as we all know, there's no problem a little homebrew can't solve. This is definitely a work in progress and doesn't at all cover alchemy or basically any other potion. As our game goes on and I find myself in need, I'll definitely add those in. But as it stands, is there anything you would add or change?

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