What?

The past couple of weeks of hot weather with sudden heavy showers has resulted in a veritable forest growing under my bird feeders (see extra). The barrel contains a little soil and several large stones and does grow a few weeds but not normally this size. The mixed seed is supposed to be 'non grow' but there are also sunflower hearts so I wonder if these are sunflowers?
I am going to pull them up anyway but may leave just one to see what it is.