I have to correct myself, the global limit is not 3 but 25, but the weight of the grass is 3, so this will be taken into account if you also have dust or spectres from paranormal.
I'm still not sure about this. I could reproduce the problem now (once) by doing the following:
1. Move to the Canter Cottage
2. Wait a little for the grass in the neighborhood to spawn and harvest all the prairie grass available in this neighborhood (there are at least 5)
3. Go to the town center
4. Also wait a little and harvest all the prairie grass available in this neighborhood (there are at least 3)
5. Go back home, wait a little and harvest the 5 grass objects again
6. Wait until 5am and see if there will spawn anything on your lot
When I did not interact with the grass in the neighborhood I'm pretty sure it always worked. So I kind of suspect that the regrowing of the grass in the neighborhood areas adds to the quota I mentioned above and prevents the grass to spawn on my own lot. But I'm not sure about this. Would be great if you also tried what I did @crinrict .
I tried to play some prairie grass based rags to riches and that really messed things up :D I know I could place the object from BB on my lot, but that feels a lot like cheating then...
