Use a general purpose potting soil to re-plant your delphinium. Be sure to pot it in a container with drain holes. When re-potting anything make sure to place the plant at the same level as it was in the previous pot — this gives the roots room to grow. Water your plant immediately after you re-pot it. You should water the plant when the soil becomes slightly dry. Fertilize about two weeks after you plant it with a light solution of plant fertilizer.

You may want to find out if the variety of delphinium you have is perennial, biennial or annual. If it is perennial or biennial may want to plant it outside. You will need to know if it is hardy in your zone before you plant it outside.