I agree with the second bit, but not the first.
Most definitely if the cops truly had a search warrant for that property, then any pot they found along the way could legitimately be entered into evidence.
But I sincerely doubt that they're going to charge the OP. They wouldn't have held him for three days and NOT charged him, if they were inclined to do so. And if they had the goods to make charges stick, they wouldn't have made him sign a statement saying that he was just "detained". The only reason to do that is to cover THEIR butts. . .implying that THEY did something wrong. If they had the goods, they WOULD have just arrested him, otherwise, holding a person for three full days without arresting them looks REALLY bad.
I conclude that the reason they didn't charge the OP is because they knew their case wasn't legally sound. . .probably because they knew the evidence they seized wasn't admissible. In fact, they might have spend some of that three day detention time going over the case with the DA to see if they could make anything stick.
So I think the OP probably dodged a bullet here.
If he feels "hassled" by the cops, he should look at it from THEIR perspective. . .they did him a HUGE favor by destroying his weed and preventing him from facing a manufacturing/cultivation charge involving dozens of plants!