Once they fill up the initial square, they aren't spreading any further. They also don't seem to be spreading up or down single blocks like normal grass. Using version 244.

By "special grasses", do you mean grasses spawned by grass seeds? Because this is expected behavious.

I was under the impression that they would continue to spread like normal grass, and were not limited to a small area. And yes, grass types like Golden or Imbued or Vivid.

"... An additional six types of Pasture Seeds can be created, for alternative grass types with various textures.
These spread to dirt like normal and can sustain any plant a block of grass can. Similarly, they may only be picked up with Silk Touch. However, they do not decay back into dirt if there's a block above them." --Lexica Botania

Unless I misunderstand either this issue, or this entry, the grass types SHOULD spread. So either the lexicon is wrong, or there is a bug which makes it not spread

It may be connected to whatever limits them to that radius when first created. Somehow, it stays limited.

I poked around in the code and found BlockAltGrass.java, the file apparently responsible for special grasses, and there's nothing in there that would cause such behavior; it doesn't even track the block/seed it originally came from. You sure your grass is well-lit?

It's out in the open, under direct sunlight. The square of scorched grass near my nether portal hasn't spread in days.

Actually, looking at it further, it isn't even filling in the square. After some time, it just straight up stops.

...I've made a lot of these seeds. Wow.

It doesn't override other grass types, just like with vanilla grass & mycelium. Only the initial burst from the Pasture Seed can do that. You need plain dirt where you want it to spread.

Not an issue, please close

No, it won't even keep spreading on normal dirt/grass.

It won't spread to grass... Dirt however? It should spread to, are you sure it's pure, vanilla dirt? Or is there a different mod that might mess with it? If so, could you also try this in just vanilla + botania

It's just vanilla dirt. It was dirt there but vanilla grass spreads much faster than these types do.

So it does spread to the dirt blocks, only slower than normal grass?

Yes, much slower.

That means this issue is not correct, could you (or someone else with that power) close this issue?