I vote for the flowers. Since your having a outdoor wedding the wild flowers fit perfect into the atmosphere of a garden/outdoor wedding.

I feel flowers can be on an invitation and still be formal, mature, and have a serious tone about an upcoming wedding. I had them in my invitations when I got married for the first and last time at age 44 years. I do believe I was mature and serious about my upcoming wedding.

You go with what feels right to you, regardless of the zillion different opinions that will come your way.