Calendar view of when each plant was fertilized

I think you're going to need a table where each record represents a single fertilization I'm afraid

Do you mean the only way is to create a table for each plant? Just to have a calendar view for a single plant? In the schedule table I can see what plants have been fertilized (though I have to click to expand to view), but it is not convenient.

Can you share the views for each table? Also, you'd like to be able to filter to 1 specific plant to see the fertilizer and schedule data? Or are you wanting the schedule to have 1 calendar view for the fertilizer used marked on the correct date?

Nah, a single table with all the fertilizations would work.  That is to say, each record would contain:
1. Fertilizer used
2. Plant fertilized
3. Date

I'm assuming your end goal is to see all fertilizations in a single calendar view like so:

To see specific plants you could just filter by the plant within the calendar view

Ok. I have "discovered" that if I make an individual record for each plant, I could have a better view in the calendar (before I put all plants and all fertilizers used in one day together in one single record).

Now I have something like this in the calendar view:

29 april
done fert1 Rosemary
done fert2 Rose

5 may
plan fert3 Hibiscus

But still impossible to view plants, because done/plan fill cells, there is little bit place for fertilizers, no place for the name of a plant.

in schedule grid: date-fertilizer-plant-done
in calendar view in each cell I could see done/plan, beginning of the name of a fertilizer, and no space for a name of plant (see the screenshot)

in fertilizer grid: name-date of used-plan date
so I could make calendar views:
-done
-plan
in both I could see only name of fertilizer

Yeah, there's not much we can do about that I'm afraid, the amount of space to display the text is tied directly to the display width of the page.  Perhaps you could try using abbreviations for the statuses/fertilizers/plant names? 

Also, is it OK to record dates of fertilization in one cell? I don't use it in grid view, so I could hide it, the question is, if airtable can handle it when its number (dates in one cell) reach >100 (I will clean it once a year).

re: Also, is it OK to record dates of fertilization in one cell

Yeah that's fine
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re: if airtable can handle it when its number (dates in one cell) reach >100 (I will clean it once a year).

Yeah it can; I've had a couple of thousand linked to a single record and it worked fine