Don't even think about it! Grass roots will compete for water and space and kill your trees... just not done. Ever.

Though grass would not actually kill the tree, it would make a difficult task much MUCH harder, but there's no law against it.

My only question is, where would you find a little wee tiny lawn mower?

Lol, I would just use scissors. I've grown grass in a small pot before and used scissors and the grass stayed small, but I see why it's unrealistic because of the roots and proper watering would be near impossible

What if u added a weed barrier over the bonsai soil and then used grassed grown from container transfer on top of weed barrier? Just a thought idk if it will work or not

If the idea of bonsai is to create a small tree that looks replicates a bigger one,than wouldn't the size ratio disqualify grass alone? Moss yo me actually resembles grass when you take into avvount the size ratio.

All that being said,I'm not a bonsai Nazi or snob,so I believe you do with your trees what makes YOU happy and throw everything else out the window!😁👍