"I've seen several container grown peony plants for sale in nurseries here in the spring. Is this advisable to purchase a plant rather than bulbs. If buying the plant is okay, should I grow it in the same container over the summer and then plant in the ground in the fall? I'm leery of planting a peony plant here in April as it normally has gotten quite warm by then and think the stress of summer wouldn't be good for it."
The question of whether to purchase a plant or a bulb is answered in the previous post 2013 Questions - Purchasing Peony Plants Versus Roots. As for the question of when to plant the container peony, that depends on how well you take care of your container plants. If you are like me, and you take care of your container plants when you have time, I would recommend planting your peony in the ground as soon as you buy it. However perhaps you are very meticulous and experienced container gardener, and you tend to your containers better than your garden. Then I would say that it would be fine to wait until fall to plant your peony in the ground.
Pink Single Peony in Pot on Deck
However I would not recommend growing your peony in the container permanently. I myself purchased a peony in a nice container years ago, thinking perhaps that it would be nice to have a peony blooming on my deck every year. Even with special care (peonies are my favorite flower after all), it continued to decline each year until it died. I'm quite sure that the peonies for sale in beautiful containers each spring are not grown to blooming size that way. They are most likely grown in super ideal conditions in the ground until they are full of buds and then stuffed into a beautiful pot, which may look nice on the outside, but it makes a sad home for a peony! Peonies actually grow very large roots underground which are needed to fuel those huge blossoms each spring. Zone 8 is actually a good zone for growing peonies. I would just make sure to plant the peony crown and eyes even with the soil level. You may want to check out my post 2012 How to Plant an Herbaceous Peony for pointers! Good luck!!!