Spiderwort or Tradescandia is a tough perennial, but it does bloom best with more sun. It prefers sandy soil and does not need much fertilizer. I do see from the image you sent that your plant has buds so it will bloom soon. The flowers only last one day however but new buds should open daily. I suggest you not fertilize this plant at all and it will have more flowers. Rich soil and fertilizer makes it grow foliage over flowers. The buds should open after a few warm days but if this does not happen I suggest you move the plants to a location with more sun. For more color in your shaded planter I suggest you consider impatients, lobelia, begonias, and coleus which are all annual plants so die in the winter and mix with hosta, saxifrage, ferns, lamiums and mondo grass which are perennials that give you color from foliage rather than flowers. If you prefer shade loving shrubs that will not disappear in the winter add some dwarf sweet box (Sarcacoccoa humilis) and dwarf Lily of the Valley Shrub (Pieris japonica) and perhaps some dwarf Nandina as these shrubs are all compact and do not lose their foliage in the winter. Keep growing, MarianneBinetti