Weeding the collection

It often falls within my job to weed the Young Adult collection in the library where I work. Sadly, we are at a great need for space in the library, so I have to weed often (and often brutally). I am always torn by some books that are borderline YA and Middle Grade. If they aren't being read in YA, do I delete them, or try them out in the JF (Middle Grade) section? How do you decide which books go where?

This weeding cycle I'm also facing the reality that I may walk home with quite a few books today. Some of these books look good! Maybe they just need a good home, someone to love them.