A seedling is a young plant that develops from a germinating seed, an early and delicate stage in its life cycle. Initially, these young plants rely on stored energy from the seed, then transition to photosynthesis as their first true leaves develop. Nurturing seedlings through this vulnerable period is important for their future health and productivity.
Essential Seedling Care
Providing adequate light is important for healthy seedling development. Most vegetable seedlings benefit from 12 to 16 hours of bright light daily, often requiring supplemental grow lights, as window light is usually insufficient. Positioning these lights just 1-2 inches above the seedlings helps prevent stretching and promotes sturdy growth. Consistent moisture is also important, but overwatering can be detrimental. Bottom watering is often recommended to ensure even moisture and prevent disease.
The growing medium plays a significant role. A sterile, well-draining, and light seed-starting mix is ideal for preventing issues and promoting root development. Maintaining appropriate temperature and humidity levels supports growth. Seedlings generally thrive in temperatures between 65-85°F (18-29°C) with humidity levels around 65-85%. Air circulation is equally important, as a gentle breeze from a small fan strengthens stems and reduces fungal problems by preventing stagnant, humid conditions.
Common Seedling Problems
Seedlings often exhibit “legginess,” characterized by tall, thin, and stretched stems, due to insufficient light. To correct this, increase light intensity or duration, ensuring light sources are close to the foliage. Overcrowding can also contribute to legginess; thinning them out provides adequate space and airflow. Another common issue is “damping-off,” a fungal disease causing seedlings to collapse at the soil line. It is exacerbated by cool, wet conditions, high humidity, and poor air circulation.
Preventing damping-off involves using sterilized pots and fresh, sterile seed-starting mix, avoiding garden soil. Proper watering techniques, such as bottom watering and allowing the soil surface to dry slightly between waterings, also deter fungal growth. Young seedlings usually have enough nutrients from their seed and starting mix, but prolonged deficiency can occur if they remain in small cells too long. Pests like fungus gnats thrive in overly moist conditions; allowing the soil to dry slightly can help manage them; sticky traps can also be used.
Transplanting Seedlings
Knowing when to transplant seedlings is important for their continued growth. Seedlings are typically ready when they have developed at least two to four sets of “true leaves,” which are distinct from the initial seed leaves (cotyledons). A healthy root system, visible through drainage holes, also indicates readiness. Before moving seedlings outdoors, a process called “hardening off” is necessary to acclimate them to harsher outdoor conditions like sun, wind, and fluctuating temperatures.
This acclimation involves gradually exposing seedlings to outdoor elements over 7-14 days, starting with short periods in a sheltered, shaded location and progressively increasing exposure to direct sun and wind. Transplanting should be done gently to minimize shock, ideally on an overcast day or in the early morning. Handle seedlings by their leaves, not their delicate stems. Plant them at the same depth they grew in their original container, though some, like tomatoes, can be buried deeper. After transplanting, immediate and thorough watering helps settle the soil around the roots and eliminate air pockets.