OH!
I knew you could abuse defertilizers like that, but I didn't knew you could stack it all in one go
I had been manually adding the fertilizer, defertilizer one by one each hour

I see, thanks for the explanation.

> if it only grows by one day when fert changes from 0 to 1, wouldnt it be more efficient to do 0 -> 1 -> 0 -> 1,

I think what you're missing is that defertilizer goes straight to -1

The defertilizer sets fert to -1.
(It will be -1 regardless of the current value, not the current value minus 1.)

+0
+1 Fertilizer (growth)
-1 Defertilizer
+0 Fertilizer
+1 Fertilizer (growth)
-1 Defertilizer
+0 Fertilizer
+1 Fertilizer (growth)

OK, but what i dont get is, if it only grows by one day when fert changes from 0 to 1, wouldnt it be more efficient to do 0 -> 1 -> 0 -> 1, presumably by alternating fertilizer and defertilizer?

As a premise, this mod does not alter the growth system. It advances crop growth by stacking fertilizers and defertilizers in the correct order based on the game's mechanics.

- There is an internal value called fert.
- Giving fertilizer increases fert by 1.
- Giving defertilizer sets fert to -1.
- The crop only grows by one day when fert changes from 0 to 1.
- When fertilizers are stacked, they are processed in the order from the top.

For example, if fertilizers and defertilizers are stacked as follows:
　　Fertilizer → Fertilizer → Defertilizer → Fertilizer → Fertilizer → Defertilizer → Fertilizer,
fert will change as follows:
　　0 → 1 → -1 → 0 → 1 → -1 → 0 → 1
Since fert changes from 0 to 1 a total of 3 times, the crop grows by 3 days.

But why does it require defertilizer rather than just stacking fertilizer to get multiple day's worth of growth?

Placing two fertilizers and one defertilizer in the correct order will advance a crop by one day's growth.

For example, if a crop has not yet been affected by fertilizer or defertilizer, placing them in the following order:
Fertilizer → Fertilizer → Defertilizer → Fertilizer → Fertilizer → Defertilizer → Fertilizer
will result in three days of growth.

This mod calculates the optimal structure based on various factors such as soil condition, crop status, and current time. With just a press of the context menu button, it will stack fertilizers and defertilizers in the correct order until the crop reaches the stage where seeds can be obtained.

(Of course, fertilizers and defertilizers are required. Items marked as important will not be used.)

Then what is this mod supposed to do? I am confused.

That's a Japanese slang term.

A Mille-feuille is a type of cake. What does your mod have to do with cakes?