Growing red salvia flowers in full sun will give you the biggest flower output. Also select a location with a loamy, well-drained soil. Amend the soil with compost.
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 and take action against slugs, snails, 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. Whiteflies are notorious greenhouse pests, and, occasionally, they will make the trip from greenhouse to garden center, undiscovered.