I had a friend living with me for close to 6 years. We had no rental agreement. I am the homeowner. He owes me $2600 in unpaid rent.
He has told friends and posted to his blog that he has moved. This was also confirmed by the mailman. Many of his belonging are still in my house.
A note was left asking details, where he moved to and if he intended on paying up. There is evidence he was in the house, although he left no reply and most his belonging remain.
Last night I changed all the locks and cleared all his belongings into the garage. My garage if FULL of his crap.
My question is: how long do I need to keep his crap? And if there is anything of value how soon do I have to wait to sell it?

A note was left asking details,

That is, I had left him a note.

Send him a certified letter telling him he has 30 days to arrange removal of his belongings. If he does not do so you will assume that he has abandoned them and you will do with them as you see fit.

You should include in the letter a bill for what he owes you. Give him a deadline for payment. Advise him, if payment is not receive you will pursue legal action to recover what he owes.

Two things. He didn't leave me a forwarding address and the post office would not give it to me. He doesn't answer or return my calls either.
Secondly, my friends and I agree, he would retaliate if I make any aggressive move- such as threatening to sue or seek recovery for the monies he owes. He is a very clever scam artist.
He has posted slanderous things about me on his Facebook and his loyal minions are eating up his every word. I fear backlash for any move I make. I truly feel the safest thing would be to not react at all. It is highly unlikely he would resort to any kind of physical violence. Living with him for so long he does know how to hurt me in other ways.
That being said, I am OK taking the hit for $2600 as long as he just goes away quietly.
So if I send his things to the dump next weekend, is that too soon? Or should I wait 30 days...

First, the PO won't give you the forwarding address, but that doesn't mean you can't send something to him at his last known address. The PO will forward it. And, if you send it Certified or Return Receipt, they will show where it was delivered to.

Second, you cannot just throw his things out. That will let you in for trouble. If you don't want to deal with him then send him a letter stating that, on such and such a date, you will move his belongings into a storage unit. Many will give you the first month free. Tell him the storage unit will be opened in his name and you will send him the location once the stuff is moved in. Also note that only the first months is paid for.

Second

Agreed, he was a tenant and has tenant rights so evict him following the laws in your state.