Salvia guaranitica ‘Black and Blue’ is a popular, heat-tolerant perennial known for its striking floral display, providing continuous color from mid-summer until the first frost. This cultivar features tubular, deep cobalt-blue flowers emerging from jet-black calyxes. Understanding its specific needs and maintenance schedule will ensure vigorous growth and abundant blooms. This guide outlines the necessary steps for successfully growing and maintaining this anise-scented sage.
Description and Site Selection
The Salvia guaranitica ‘Black and Blue’ forms an upright, shrubby clump, typically reaching 3 to 5 feet high and spreading 2 to 3 feet wide. Its flowers, featuring black bases and deep blue corollas, attract hummingbirds and butterflies. While it behaves as a tender perennial in USDA Hardiness Zones 7 through 10, gardeners in colder regions often cultivate it as an annual.
Choosing the correct location is important for maximizing flowering potential. Full sun exposure (at least six hours of direct sunlight daily) promotes prolific blooming and prevents stems from becoming weak or “leggy.” Although it can tolerate partial shade, too little light diminishes the plant’s density and flower count.
The plant requires well-draining soil to prevent root rot. While it tolerates average garden soil, amending the planting area with organic material, like compost, is recommended to support vigorous growth. A neutral soil pH is suitable, and ensuring the site is not prone to waterlogging contributes to the plant’s long-term health.
Planting and Initial Establishment
Timing the planting correctly is crucial. These plants are sensitive to cold and should only be placed outdoors after the threat of the last spring frost has passed. Planting too early risks damage to the root system and new foliage, slowing establishment.
Dig a hole twice as wide as the root ball but no deeper. Gently loosen any tightly bound roots before planting, ensuring the top of the root ball remains level with the surrounding soil. Allow 2 to 3 feet between plants to ensure good air circulation, which helps deter fungal diseases.
Backfill the hole with soil, gently firming it around the base to secure the plant and remove air pockets. A thorough initial watering is necessary to settle the soil around the roots. During the first few weeks, maintaining consistent moisture encourages a strong, deep root system, which is foundational for later drought tolerance.
Ongoing Maintenance and Pruning
Once established, watering needs shift from constant moisture to deeper, less frequent applications. The plant becomes drought-tolerant, but performance is best when supplemental water is provided during extended dry spells. Watering deeply encourages roots to grow downward, making the plant more resilient to heat.
To support the extended bloom cycle, regular feeding is beneficial, but avoid over-fertilizing as excessive nitrogen promotes foliage over flowers. Apply a balanced, slow-release fertilizer (such as 10-10-10) in early spring. During peak blooming, switching to a formulation with a slightly higher phosphorus ratio encourages the production of new flower spikes.
Routine pruning, known as deadheading, is important for continuous flowering and prevents the plant from putting energy into seed production. Remove spent flower spikes to the nearest set of healthy leaves or buds to encourage new growth and subsequent blooms. The plant can also be lightly pinched back during early summer to reduce height and promote a denser, bushier shape.
Pest and disease issues are generally minimal. Powdery mildew can occasionally appear in humid conditions or when air circulation is poor, managed by ensuring proper spacing and avoiding overhead watering. Spider mites may also target the foliage, controlled with a strong spray of water or an application of insecticidal soap.
Preparing for Dormancy and Propagation
In mild climates (USDA Zones 8-10), where winter temperatures rarely drop below 20 degrees Fahrenheit, the salvia can be left in the ground as a perennial. Leave the foliage and stems standing through winter, as this provides insulation and protection for the crown. In late winter or early spring, cut the old woody stems back to 6 to 12 inches above the ground before new growth begins.
For gardeners in colder regions (Zones 7 and below), the plant is best treated as an annual or overwintered indoors. To save the plant, cut it back, lift it from the garden, pot it, and move it to a bright, cool indoor location before the first hard frost. Propagation using stem cuttings taken in late summer or early fall is a reliable preservation method.
Softwood cuttings, taken from the tips of non-flowering stems, are ideal for propagation. Take a cutting approximately four inches long just below a leaf node, removing all but the top two sets of leaves. The cutting can then be placed into a well-draining rooting medium or a glass of water, where roots typically form within a few weeks, creating a new plant to be grown indoors until spring.