The Salvia guaranitica ‘Black and Blue’ is a highly sought-after plant recognized for its striking appearance. This cultivar features deep cobalt-blue flowers emerging from nearly black calyces, creating a vivid contrast. It is a fast-growing plant that provides excellent vertical interest and attracts hummingbirds throughout the summer and fall. Its perennial status depends greatly on the local climate, which is the primary source of confusion for gardeners.
Understanding Its Perennial Status
The classification of ‘Black and Blue’ Salvia is best described as a tender perennial. This means its ability to return year after year depends on winter temperature minimums. A tender perennial functions as a perennial in mild climates but cannot withstand sustained deep freezing in colder regions. It has a root system built to survive mild winters, but not severe, prolonged freezes.
This plant is reliably winter hardy in United States Department of Agriculture (USDA) Hardiness Zones 8 through 10. In these zones, it typically dies back to the ground and regrows vigorously in the spring. Gardeners in Zone 7 are on the border; survival is not guaranteed, though the plant sometimes returns after a mild winter. In Zone 6 and colder, the plant is typically treated as an annual. Its status as a perennial or annual is determined by the specific geographical location and winter severity.
Standard Growing Needs
‘Black and Blue’ Salvia thrives best when situated in a location that receives full sun, though it can tolerate light afternoon shade. Full sun encourages prolific flowering and helps maintain a sturdy, upright growth habit. If the plant receives too much shade, the stems may become elongated and weak, causing them to flop over.
The plant prefers well-drained soil rich in organic matter, such as loam. While it appreciates consistent moisture, especially when establishing itself, soggy conditions must be avoided to prevent root rot. Once established, it tolerates periods of drought, though supplemental watering during dry spells supports continuous blooming. To maximize flower production, spent flower spikes should be removed (deadheading), which signals the plant to produce more blooms from mid-summer until the first frost.
Strategies for Winter Survival
Gardeners in marginal areas, particularly Zone 7, can increase the plant’s chances of survival by applying a thick layer of organic mulch. After the plant dies back from the first hard frost, stems should be cut down to about six inches above the crown. A heavy covering of organic material, such as straw, shredded leaves, or wood chips, should be placed over the root zone to a depth of four to six inches. Keep the mulch from directly covering the central crown, as this can trap excess moisture and lead to rot.
For those in Zone 6 and colder who want to save their plant, the most reliable method is lifting it for indoor dormant storage. Before the ground freezes, the entire plant should be dug up, preserving the main root ball. The top growth should then be cut back dramatically, leaving only a few inches of stem above the soil line. The root ball can be potted into a container, or if the plant is large, the root system can be carefully divided into smaller sections.
The potted plant needs to be moved to a cool, dark, and non-freezing location, such as an unheated garage or cool basement. The ideal storage temperature is just above freezing (35 to 45 degrees Fahrenheit), which encourages dormancy. During this period, the plant requires very little water, perhaps only a light watering once a month to prevent the root ball from completely desiccating. Container-grown plants can be moved indoors, trimmed back, and treated similarly, allowing the gardener to replant a mature specimen the following spring.