Hi, I use grass clippings around my garlic and onions and they work very well. They pack down with a few waterings. I put them around 3 inches thick.
Gary

I've also done that. Unlike many other vegetables, it seems that alliums are not affected by close contact to fresh grass clippings. And since onions and garlic appreciate extra nitrogen after they are established, that's an added bonus.

Martin

I use grass clipping mulch for my garlic. One thing to watch out for is that grass clippings can create a very heavy mat if they are too thick and wet. I had areas that were like corrugated cardboard.

Around here we usually have some leaves on the ground at garlic planting time. These get mowed in with the grass clippings. If not, I'll bust a bale of straw and spread some around (near the garden) before I mow. Then I use this 'mixture' for the mulch. The leaves and/or straw tend to reduce (at least in my experience) the possible matting of grass alone.