Breaking Out Hair with Render Layer

I’m using a hair particle system to create grass. I’ve broken the grass out to its own render layer but am having a terrible time getting it merged back into the other render layers. I’m getting edge alpha artifacts big time!

I imagine this is probably a Premul issue, or something similar, but I’ve tried just about everything and cant get the grass to re-combine with other layers.

Can someone have a look at my node setup and let me know what might be wrong?

Thanks a million!

http://www.skwerm.com/blender/GrassAlpha.jpg

Does it come out that way in the render? Also, is the end of your hairs set to a negative value?