I do grow Doryanthes palmeri, which is smaller than excelsa, but more attractive to me. This has a shorter stalk (you don't need a ladder to see the flowers !) which bent over the wight of the showy red flowers. It develops a rather large clump with the years, but it could be grown in container, while I doubt excelsa will work. Also, palmeri is said to be hardier than excelsa. Formerly placed in Agavaceae (now I don't know) it is similar for the growing aspects to Hesperaloe or better Beschorneria, as the head that flower will die after flowering, but the suckers will grow on their own roots. I don't know if they should be considered geophytes, as they have just a thickened base under the soil. Better definition would be herbaceous perennials. Angelo Porcelli P.S. Alberto, glad to hear from you again