Activity for JanisV

Opinions welcomed please! !! So I'd like to start getting my vases for my reception next Oct. .Thank gawddddd for Michaels coupon because I'm going to need a lot. But...do I get the tall thin ones and put branches or the shorter ones and fill with...

For a round table in a somewhat round room, am I going against the "rules" if I were to use the square glass center pieces? Opinions please I plan on filling each with various fall items.