Before planting flowers, trees, bushes, etc. it would be a good idea to check to see if the plants are toxic to poultry. I think (?) most animals will instinctively avoid things that are poisonous to them, but if someone is going to free range their flock, it might still be a good idea to check...
Our chickens loved to roam in the garden once we were done harvesting so we made sure to not use chemicals when we gardened.
Also, recently there was a distraught post from someone about their chicken getting into rat poison that had been set out. So important to keep poisons out of any place...