Uh, I think it getting wet is bad, but I'm not real sure. I normally put out sunflower seeds and keep it in a bird feeder with a roof.
I put the thistles out one time, but all the birds that they claim will only eat thistles, come over and eat the sunflower seeds.
Plus, the seeds last a lot longer than the thistles or the mixed bags with that corn looking stuff in it, they take longer to open up the seed and they don't scatter.
If money is tight, you don't have to have a feeder, you can just put some out in a bowl everyday, they will eat from it.