How to get variance in texture

recently I’ve created my own level and painted some textures on the ground. This worked pretty good so far but now I realize that there are a lot of lines between two texture instances. It looks like that a lot of textures were set in a row (as you can see in the picture).

Now I want to know: how do I get variance in those textures so that these lines disappear?
Thank you!

There is old article with example techniques how to reduce visibility of such patterns.