You can pot it up until the fall. Remember, tree peonies don't like wet roots and they are cold weather plants. The colder the winter, the better the bloom. I would let it sit outside in the full sun in the pot and see what happens. Don't expect any major growth soon because you have disturbed the plant's cycle. Remember also that growing and nurturing tree peonies takes a long time to see results. You must be patient. In the fall, place it in the ground at a well drained site. Fertilize when planted, once in the spring when new growth starts and after blooming. Use a low nitrogen fertilizer like Neptunes Harvest (called simply Fish Fertilizer at Lowe's and Home Depot). Good luck.
