How long must we wait until it is considered property abandonment?

A acquaintance of ours moved out of there home and asked us if they could keep some of there stuff at our house. A lot of what they stored at our home is in a unlocked shed and can be considered pretty valuable. They asked if they could keep it at our place for a couple weeks and they would return for their stuff shortly. It's now been 3 months and they haven't contacted us to get their stuff nor have they taken their stuff freely( It's all outside in the unlocked shed) They wouldn't even have to call and set up a date and time to get it..... I do not want this stuff there any longer and be responsible for it anymore.... They assured us it would be gone by now. Personally I would like to keep some of it and get rid of a lot of the junk (things they even acknowledge is trash and said they'd dispose of it.) When is it considered property abandonment? We are moving into another home in 2 month and if we leave this stuff here we ill be charged by the rental agency to dispose of it. We have tried to contact them only once and received no call back but I do not feel it is our responsibility to chase after them to come back and get their property. I already feel like we have gone out of our way to help them bring the stuff here and store it for free. These people are hardly considered friends and mainly friends of other friends that we don't even talk to anymore