Peonies are especially needy when it comes to staking. Properly supported, these perennials hold their beautiful fluffy blooms high and dry - not sprawled around them to be trampled and soiled. Staking is not only for appearance's sake. Many perennials are top heavy and bent stems function poorly. Cracks are entrances for rot organisms.
In the past, I've used tomato cages, (both upside down and right side up) to direct the stems of peonies upwards. Here’s a clever method of adapting these cages to provide attractive support for many different types of ornamental plants, including dahlias. Cut the legs off the cage, right beneath the smallest circle. Bend the end of each leg to make a hook. Place the modified cage upside down over the plant so that the smallest 'circle' is on top, then drive the leg-pins into the ground, placed at even intervals, to snag the bottom ring to hold it in place. You can twist-tie a label to the top ring for easy identification of each plant.
Here's another handy tip you may want to try before plants get too large. It involves the use of a large plastic lid. Cut out the centre of this lid leaving an outer border at least an inch wide. Now make four evenly spaced x shaped cuts in this border. Insert four stakes into the ground matching the spacing and pattern of the x's on the plastic lid. Slide the lid over the stakes, through the "X" cuts in the edge, adjusting it to fit around the plant. The "X" cuts lightly pinch the stake, so the lid stays in position until you move it up the stake as the plant grows.
For some tall plants, you might want to slide more than one cut lid on the stakes and adjust them independently as the plant grows.
I've seen staking arrangements that use three or four posts driven into the ground around the plant. String or coated wire completes the square or triangle and sometimes a network of crisscrossed string between these posts further aids the stems in keeping upright. This method does a great job and would be ideal if you want to harvest the blooms as cut flowers.
Personally, I prefer inconspicuous staking methods that perform the function without detracting from the beauty of the plant. Stakes should be six to twelve inches shorter than the mature plant and ideally are the same colour as the foliage.