Unwanted trees- Is there anyway I can get rid of these trees forever?

Are you pulling the tree starts up by the roots? If not, dig them up roots and all.

Oh Peggy I am so sorry to hear this. It sounds to me like your "tree" sprouts are growing from underground rhizomes (perhaps with spreading roots?), and you may have to transplant those beautiful lillies somewhere else until you deal with digging out the rhizomes and roots :( That is a lot of hard work and not the solution you want to hear, I am sure, but that is what it sounds like to me and how I would deal with it. Once you have the area cleaned up/cleared out, then you could move your lillies back to their home spot and not have to worry about "tree sprouts" again. I wish I could give you a happier and easier answer than this, but I can't think of one :( So sorry.

I have cut them off and brushed on weed killer on only the cut, it may take more than one application, but it even killed wild grape that is hard to kill. Just use a small junky, cheap nylon artist brush so that you don't get it on your Lilly's.

Try drilling a hole in the base of trunk and pour weed killer into hole.It should slowly kill the roots off.

Buy Tordon RTU ( farm stores carry it). Cut off tree at ground level; amply squirt on Tordon -- it won't grow back!