You might try growing some from seed if you are worried about chemicals. These are some easy to start from seed flowers and plants my ducks like. Each duck is different and your experience could be different from mine with these plants.
Zinnias - they get pretty tall, the ducks nibble at the leaves and leave the flowers alone.
Borage - hairy coarse leaves that taste like cucumber. Blue flowers also taste great, but ducks strip the plant bare of leaves leaving the flowers for me to nibble on.
Johnny jump-ups and pansy - They browse on this when they are in the mood.
Dianthus - They eat the leaves, but never strip the plant bare.
Chard - Rainbow varieties are very colorful
Lettuce - Super easy to grow but gone in an instant unless you have a lot of it and a way to protect it until its larger. So many varieties, colors and textures.
Nasturtium - My ducks don't eat these, maybe too peppery. They are safe to eat if they wanted too...
Not from seed but you might consider
Mini roses - grows well in a pot, they eat the buds and flowers. Don't spray with chemicals.
Blueberry bushes - very pretty shrubs in a variety of shapes and sizes, grows well in a pot of half peat moss and half potting mix.