Select peonies that are almost fully open. Cut the flowers early in the morning if using garden-fresh flowers. Using flowers that are in various stages of maturity, some fully opened, some partially closed, will create a more appealing arrangement and help it last longer.
Remove any leaves that will be below the water line as they will decay quickly and cloud the water in the vase. When ready to arrange the peonies, cut the stems another 1 to 2 inches while holding under water. Cutting stems underwater helps the water to cling to the cut end, blocking air from getting in and causing the flowers to dry out quicker.
Select a vase, or any type of container that you wish, such as a clean coffee can, glass ice cream dishes, glass soda bottles or a milk glass footed fruit bowl. Wash out the vase or container you will arrange the peonies in using hot, soapy water and rinse well.
Fill the vase or container about half full with room temperature water. Add flower food, available at a local florist, to the water and stir until dissolved.
Place the peonies in the vase or container, re-cutting as necessary to fit. Remember to re-cut the stems underwater. Place taller flowers in the center of the arrangement, adding shorter flowers around the outside edges. If needed, add more water to the vase.
Place the peony arrangements in a cool location away from heaters, wood stoves or other heat sources which will dry out the flowers quicker. Keep the arrangement out of direct sunlight to help prolong the life of the flowers and add fresh water every couple of days to keep the flowers fresher longer.