Means, that maybe two or one component will rise the fertility to rich soil 140%, second +40% and third +40%, to 220%.

One needs to respect the growth advantage of the Hydroponics basin with 280% growth rate, it cost electricity and not less.

I would implement a requirement for the sewage distribution, to hold this rate up. If not the soil will degrade to 140%. There needs to be a motivation to do it one times, but an advantage if one does it actively.

However, it would be much done, if it just requires the substance of the DBH for construction, like stone brick for a floor.

Do you know Vintage Story, they name there a "simple" fertilizer mechanic, if you bring it to the ground plants will grow faster if they depend on this kind of fertilizer.

https://wiki.vintagestory.at/Farming

You mentioned a problem that having a too high growth rate is implanced, this maybe would be the solution, then to give every plant its dependency. One could do that, if he wanted, it would be simpler to say, there are three types, and if you bring one of them this base growth rate rises, and if you bring the other two it rises two times.

The relevant element is "rich soil" with 140%. In Vintage Story synthetically fertilizing is higher effective as natural growing, the best solid can only be created from the player.

https://rimworldwiki.com/wiki/Plants

@Entity I want this mod to remain fairly simple but I do think that's a good idea. I might make a patch for DBH later though.

I prefer to have this based on human or animal sewage as resource to build this soil, some compostation. Another alternative would be to burn down crops, futurly to get vulcan ash and distribute it.

Dubs Bad Hygiene:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=836308268

This mod contains already an sewage fertilizer, you could use it.