You don’t say what kind of salvia you are growing. Are they the common red-flowering annual plant also known as scarlet sage, or a blue-flowering annual salvia? These plants don’t stay in full bloom constantly. As older flowers die out, the plant often goes green for a while until new flower stalks develop. This is especially true with new, younger plants. Also, be sure the plants have plenty of sun. Salvia requires at least 6-8 hours of direct sunlight per day. Perennial salvias also go through cycles of bloom. Once flower stalks fade, trim off the dead blooms, and within a few weeks the plants start sending out another flush of flowers.