Trees from Sedum Flowers

I have collected dried sedum flower heads to make trees for my N-scale layout. I will be making these trees over the next several months. Should I dip the flower heads in glcyerine to preserve them now or wait until after I have painted them.

Offhand, I’d guess dip’em in glycerine before you paint because the paint might seal them so that the glycerine wouldn’t penetrate.