Quick answer
The cannabis seedling stage lasts about 2–3 weeks. During this time, your plant develops its first true leaves, builds a root system, and prepares for vegetative growth.
If your seedling is stretching, drooping, yellowing, or growing slowly, it’s usually caused by light, watering, or environmental issues.
How long is the seedling stage?
Most cannabis plants stay in the seedling stage for 14–21 days, depending on:
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genetics
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environment
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light intensity
After this, they transition into the vegetative stage.
Week-by-week breakdown
Week 1 (Days 1–7): Sprout to first leaves
What you’ll see:
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Cotyledons (round starter leaves)
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First serrated leaves forming
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Very slow, fragile growth
What it needs:
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Light: low intensity, close distance
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Water: minimal, avoid soaking
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Humidity: around 65–70%
Common issues:
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Seedling falling over → weak light or overwatering
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No growth → low temperature or poor germination
If your seed didn’t start strong, check:
https://ilgmforum.com/t/how-to-germinate-cannabis-seeds-step-by-step/
Week 2 (Days 7–14): Root development
What you’ll see:
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2–3 sets of true leaves
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Faster growth
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Some vertical stretch
What it needs:
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Slightly stronger light
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Controlled watering (let medium dry slightly between watering)
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Light airflow to strengthen stems
Common issues:
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Stretching → light too far away or too weak
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Drooping → usually overwatering
Related:
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https://ilgmforum.com/t/why-are-my-seedlings-stretching-leggy-seedlings-fix/
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https://ilgmforum.com/t/how-often-should-i-water-cannabis-plants/
Week 3 (Days 14–21): Transition to vegetative growth
What you’ll see:
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3–5 nodes forming
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Stronger stem
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Noticeable daily growth
What it needs:
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Increased light intensity
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Optional light feeding (only if needed)
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Preparation for transplant
Common issues:
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Yellowing → early nutrient or watering imbalance
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Slow growth → root zone or environmental issues
How big should a seedling be after 2–3 weeks?
By the end of the seedling stage, most plants will:
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have 3–5 nodes
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be around 10–20 cm tall (depending on light and genetics)
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show steady daily growth
If your plant is much smaller or stretching heavily, something is off.
Watering seedlings (where most growers go wrong)
Overwatering is the most common mistake during the seedling stage.
Best approach:
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water in a small circle around the plant
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let the top layer dry slightly before watering again
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avoid soaking the entire pot early on
Full breakdown:
https://ilgmforum.com/t/overwatering-vs-underwatering-cannabis-how-to-tell/
Ideal environment for cannabis seedlings
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Temperature: 20–25°C
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Humidity: 60–70%
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Light cycle: 18/6
Dialing this in early makes a big difference later.
More details:
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https://ilgmforum.com/t/ideal-temperature-for-cannabis-plants/
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https://ilgmforum.com/t/ideal-humidity-for-cannabis-full-guide/
When to transplant seedlings
You’re ready to transplant when:
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roots are filling the container
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the plant has 3–4 nodes
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growth is speeding up
Guide:
https://ilgmforum.com/t/when-to-transplant-cannabis-seedlings/
Common seedling problems (quick overview)
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Stretching → light issue
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Drooping → overwatering
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Yellow leaves → nutrient or watering imbalance
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Slow growth → environment or root issues
If you’re dealing with stretch specifically:
https://ilgmforum.com/t/why-are-my-seedlings-stretching-leggy-seedlings-fix/
Discussion
What stage are your seedlings in right now?
If you want feedback, drop:
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your day/week (e.g. day 10)
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your light + distance
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a photo
You’ll usually get quick, practical advice from other growers.
