Key takeaways
- Seedlings need bright light immediately, not a windowsill.
- Use a light, sterile seed-starting mix, not garden soil.
- Keep the mix evenly moist but never waterlogged.
- Harden off before moving seedlings outside.
What seedlings need
A seed needs moisture, warmth, and — the moment it germinates — strong light. Most home failures are leggy seedlings that stretched because they were on a dim windowsill. A grow light close to the seedlings, run 12 to 16 hours a day, prevents the pale, weak, bent stems that never recover.
Setting up
Fill small containers with a light, sterile seed-starting mix and moisten it before sowing. Sow at the depth the seed packet states — a common rule is twice the seed's diameter. Cover the container with a clear lid or plastic until germination, then remove it.
Light, warmth, and water
Place the tray under a grow light set a few centimeters above the seedlings, raising it as they grow. Most seeds germinate best at warm room temperature, around 20 to 24 degrees C. Water from below or with a gentle mist, keeping the mix evenly moist without soaking it.
Thinning and potting on
Once seedlings have their first true leaves, thin to the strongest plant per cell and pot on when roots fill the container. Use a small pot with drainage and a general mix, and keep them under the light — the light is the difference between stocky seedlings and leggy ones.
Hardening off
Before seedlings move outdoors, harden them off: over 7 to 10 days, gradually introduce them to outdoor conditions, starting with a shaded, sheltered spot for an hour or two and building up. Skip this and sun and wind can kill a perfectly healthy tray overnight.
Common mistakes
Too little light, soggy mix, sowing too deep, and skipping the hardening step are the usual failures. Damping off — seedlings collapsing at the soil line — usually follows cold, wet, crowded conditions, so use fresh mix, avoid overwatering, and keep air moving.
Frequently asked questions
Do seeds need light to germinate?
Some seeds need light, some need darkness — follow the packet. But every seedling needs strong light immediately after germination to grow stocky instead of leggy.
How close should a grow light be to seedlings?
Close enough to prevent stretching — commonly a few centimeters above the tray, raised as they grow. Follow the fixture's guidance and watch for bleaching.
What is damping off and how do I prevent it?
It is a seedling disease that collapses stems at the soil line, usually in cold, wet, crowded conditions. Use fresh sterile mix, water carefully, and keep air moving.
When should I start seeds indoors?
Follow the packet's weeks-before-last-frost date for your area. Starting too early produces big, root-bound seedlings; too late delays the harvest.
Propagation results vary with plant health, season, light, and humidity. Use this guide as a starting point and adjust to what your plant shows you; when a cutting fails or a plant is unhealthy, address the underlying condition before trying again.
