Dear …
On behalf of __(Name of Organization)__, I want to thank you for the flower arrangement you sent over for our opening. The arrangement is beautiful and has made a wonderful place setting on our __(type of furniture it sat on)__. It was thoughtful of you to support us in this way during our opening. We greatly appreciate it.
I am happy to report that our opening was a resounding success. We had approximately __(number)__ of people attend. The __(food and drink/sale/etc.)__ was greatly received and all of us enjoyed visiting with our guests very much.
Again, thank you for your support through the flowers you sent. We are still enjoying the beautiful bouquet.
With thanks and best wishes,