Fake plants behind speakers a good idea?

I once had real plants around my left speaker. A friend brought a Crown RTA over. When I looked at the output, all I saw was a comb filter effect. I said what is this? He said let us remove the plants. Afterwards, there were still problems, but the comb filter was gone.

I should say these were big leaved plants. Maybe a Boston fern would not do this. I have no plants in the room where I have my system.