Coleus is a popular ornamental plant, cherished for the striking, variegated colors of its foliage rather than its small flowers. Native to tropical regions, these plants are often grown as annuals in cooler climates, providing vibrant color in gardens and containers. Growing Coleus from seed is an economical and rewarding method that allows access to a greater variety of unique patterns. Cultivating these plants from seed to a full, decorative size involves distinct phases and specific care requirements.
Preparing for Sowing and Optimal Conditions
The journey to a vibrant Coleus begins with precise timing, typically starting indoors 8 to 10 weeks before the last expected spring frost. Use sterile seed-starting trays and a fine, well-draining seed mix to prevent pathogens. Coleus seeds are minuscule and require light to germinate.
The seeds should be surface-sown, lightly pressed onto the moistened soil mix without being covered. The ideal soil temperature for germination is between 70 and 75°F. A heating mat beneath the tray can maintain this warmth. Covering the tray with a clear dome or plastic wrap helps retain the high humidity necessary for sprouting.
The Initial Germination Timeline
Once sown, the initial sprouting phase is relatively quick. Coleus seeds typically take 7 to 14 days to germinate and push a tiny sprout above the soil line. Germination up to 21 days is possible if the temperature fluctuates.
The first leaves to appear are the cotyledons, which are small seed leaves that look very different from the mature foliage. Soon after, the first set of “true leaves” will emerge. These resemble miniature versions of the adult leaves and often display the first hints of the plant’s final coloration. Keep the soil consistently moist, but not saturated, during this early stage. Watering from the bottom can help avoid dislodging the fragile seedlings.
From Seedling to Mature Plant
The period from the development of true leaves to a plant of decorative size is the longest phase, requiring an additional 8 to 10 weeks. Once seedlings have developed two to three sets of true leaves, transplant them into individual, slightly larger containers. This gives the root systems space to expand and is the time to introduce a half-strength liquid fertilizer.
Pinching is necessary for shaping the Coleus into a bushy, full specimen. This involves removing the growing tip of the plant just above a set of leaves, encouraging the plant to branch out laterally. Pinching should begin when the plant is about six inches tall and continue periodically. Remove any flower stalks that appear to redirect energy into foliage production.
Before moving plants outdoors, they must undergo a “hardening off” period. This should only happen after all danger of frost has passed and night temperatures remain above 60°F. Hardening off involves gradually exposing them to outdoor conditions over a week or more to prevent transplant shock. From initial sowing, the total time to achieve a sizable, decorative Coleus plant ready for the garden is generally 10 to 12 weeks.