When you're planning a summer garden and want an intense red flower, don't overlook annual salvias (Salvia splendens). Also called scarlet sage, these easy-to-grow plants grow as annuals in all U.S. Department of Agriculture plant hardiness zones, brightening borders and mixed beds with flaming red color all summer long. Annual salvias come in several cultivars that bloom nonstop when given good light and some basic care.
Salvia plants are bushy and highly ornamental, with brilliant, scarlet-red flower spikes held above the plant's foliage. Red salvia grows in full sun or partial shade, but the amount of sun the plant receives can affect its performance. Flowering is generally best in full sun, except in areas with extra-hot summers, where strong sun for the entire day can scorch the plant. In these regions, salvia does best in a spot that gets morning sun, followed by light shade in the hot afternoon hours. Salvia can also grow well when gets partial shade for the entire day, although the plant may be less bushy and flowering less profuse under these conditions.
You can grow salvias easily from seed, starting four to six weeks before your last frost date. Salvia seeds need light to germinate successfully, so sow seeds on top of moist potting soil or soil-less mix. You can use peat pots, sowing one or two seeds in each pot, or scatter the seeds in a flat or tray. Keep soil or mix evenly moist until seedlings emerge, then move the new plants into a bright, indirectly-lit spot, turning them every few days. When outdoor soil remains above about 60 degrees Fahrenheit and seedlings have several sets of leaves, you can transplant them outdoors, but harden them off for a week in a partially shaded spot first. When starting with purchased seedlings, choose sturdy plants that are multi-stemmed and have small flower buds.
Watering salvia plants regularly, especially during dry spells, can help keep flowers coming during the entire summer. While salvias need even moisture, they don't do well in wet, soggy soil, so if your soil drains poorly, add fine sand at planting to improve its drainage. You can also help keep salvia plants growing and blooming by fertilizing them monthly with a balanced, 20-20-20 formula, diluted at a rate of 1/4 teaspoon per gallon, but check the package label for additional instructions. To encourage branching and many sets of flower buds, pinch back the growing tips of salvia plants when they're about 4 inches tall. As flowers fade and dry out, cut flower stems back to keep the plant producing new buds.
Several different cultivars of annual red salvia are available at nurseries and garden centers. Examples include "Bonfire," also called "Clara Bedman," with heavy flower production on plants that generally grow to 26 inches in height, and "Carabiniere," a shorter, 10- to 12- inch tall variety that's extra-bushy and has fiery red flowers. Some plants vary their flower color a bit, including "Top Burgundy," which is an early-bloomer with dark red to burgundy flowers on 12-inch-tall plants, and "Laser Purple," with deep purple flowers that resist fading, even in strong sun.