They need specific weights: 7.5, 5, 2.5, and 1 pounds (I think). It doesn't matter what you put on there as long as it has the specific weight. I can't remember which one I'm looking at in that screenshot, but you should at least know what weight it requires now.
In that case filling up a vase with thrash from your inventory until it reaches the set weight hsould do the trick as well.
Nice
