Taxonomy and Botanical Type for Red Salvia
Plant taxonomy classifies red salvia plants as Salvia splendens. Despite an official common name of "scarlet sage," many people refer to the plants simply as "red salvia," which is the usage I employ.
Indigenous to Brazil, where they grow as perennials due to the hot climate, red salvia flowers are treated as if they were annual plants in temperate zones: they are damaged by hard frosts and will not survive through cold winters.
What the Plant Looks Like
Although the scarlet varieties are the best known, Salvia splendens does come in other colors, including white, salmon, pink, purple, lavender, burgundy, and orange. Salvia splendens reaches 18-30 inches in height. Its flowers grow on spikes and are quite showy -- thus its popularity.
Growing Red Salvia: Sun and Soil Requirements, Care
To improve their looks and encourage better flowering, deadhead red salvia plants. You can do this by pinching off the flower spikes with spent blooms. Make your pinch fairly far down on their stems. Be on the lookout for snails, slugs and whitefly, all of which may bother red salvia plants. In fact, when shopping for plants at the garden center, carefully inspect the undersides of the leaves for whitefly right then and there, to avoid bringing any home with you.
Whitefly is a notorious greenhouse pest, and occasionally they will make the trip from greenhouse to garden center, undiscovered.
Most gardeners will fertilize the plants with the same balanced fertilizer that they use to fertilize their other annuals, often applying it with a hose-end sprayer while watering.
Uses for Red Salvia in Landscaping
Red salvia flowers can form a striking accent when massed together as bedding plants or lined up in a row as edging plants. They are also popular in container gardens, where they can serve as a vertical accent (surrounded, for example, with white sweet alyssum and/or silvery dusty miller).
Along with geraniums and impatiens, they are perhaps the first flowers that come to mind for many folks when using annuals to inject a splash of red into the landscape. This makes them valued by those in the USA putting together red, white, and blue flower displays for the 4th of July holiday and for Memorial Day decorations. But because scarlet plays well with other colors used in autumn themes (especially yellow, such as yellow Chrysanthemum flowers), there is still a place for them even when you flip August's page on the calendar over to September's -- as fall flowers. For this reason, I recommend pinching and deadheading them during the summer, so that, when early fall rolls around, they will still be in good enough shape to supply your landscape with vibrant color.
Red Salvia Flowers, Salvia Officinalis, and Other Plants in the Genus
You will remember that I said that "scarlet sage" is one of the common names for this plant, so let me warn beginners not to confuse the red salvia flowers that we have been discussing with Salvia officinalis.
The latter is the culinary herb better known as "sage" and was also used medicinally going back to the Greeks and Romans (hence the genus name, which comes from the Latin for "save"). A more colorful version of this plant is the Tricolor sage.
Another famous (or -- depending on your point of view -- infamous) relative is Salvia divinorum, which is a hallucinogenic drug.
What is priceless to behold is when the beginning gardener who had previously grown only annuals discovers the fact that there are types of salvia that are hardy perennials in the North. The most popular kinds, however, have not red, but bluish or purplish flowers. An example is 'May Night' salvia.