This was a new obstacle for me last year: I didn't want to use plants that the ponies would like to eat and, obviously, I also didn't want to use anything that could harm them. In the end, I decided to try using rocket (spicy salad leaf) thinking that they wouldn't like the taste but that it equally wouldn't harm them. Of course, Fat Pony had to try it.... but, I thought to myself, "well, he won't try it more than once, surely"....... Suffice to say, the Arch ended up rather bare, so it was lucky that no actual points were awarded or taken away for amount of flowers on the arch!
This year, I've decided to use plastic flowers!