Mum plants can be transplanted into the garden as long as the ground is not frozen. Enjoy the potted plant indoors until it is done blooming than cut off the flowers and the stems. Remove the plant from the pot and plant it into well worked soil that you have loosened up with a shovel or spade. Add some compost if your soil is dry or sandy. Mums like at least half a day of sun. Next year your mum plant should flower again. As for the lilac, I am not sure why one is not doing well - perhaps you can send a photo or give me more details on what the foliage is looking like. Keep growing, Marianne Binetti