Cannabis Seedling Stage: Week by Week (Weeks 0–2)

3 min read

A cannabis seedling progressing from sprout with cotyledons to first true serrated leaves

The seedling stage is short, slow-looking, and oddly nerve-wracking — you’ve a tiny plant and a strong urge to do something. Knowing what’s normal each week stops you intervening when the plant is fine, which is exactly when most seedlings die. Here’s the first fortnight, week by week.

The short version:

  • Days 1–3: nothing visible — the taproot and stem work underground
  • Days 3–5: the sprout breaks the surface, often wearing the seed shell
  • Days 5–7: the round cotyledons (seed leaves) open
  • Days 7–14: the first true serrated leaves appear
  • Threats are all “too much”: water, light, nutrients, and fidgeting

Want the full breakdown? Keep scrolling.

Week 0–1: germination to sprout

After the taproot goes into a small pot of light (low-nutrient) mix about a centimetre deep, the visible action stops for a few days while the root pushes down and the stem pushes up — 2–5 days from planting, sometimes longer. The urge to dig in and check is almost physical; don’t. Days 3–5 the pale stem breaks the surface, often still wearing the seed shell like a hat (normal — it usually falls off, and if it sticks, mist it and ease it gently, never pull). Days 5–7 the two round cotyledons open — these aren’t true cannabis leaves, they’re the seed’s stored energy, and they’ll yellow and drop later, which is fine. Water with a spray bottle, keep the medium lightly damp (lift the pot), run a gentle fan, and keep the light soft and far — 60–75cm for an LED.

Week 1–2: first true leaves

Days 7–14 the first set of real, serrated cannabis leaves appears — usually a single finger, then three fingers on the next set. The plant is now photosynthesising on its own and building roots below. The environment it wants is less than you’d think: 18–24 hours of soft light, 65–70% humidity (a clear dome or cut bottle helps, removed once true leaves show or you invite damping off), 20–25°C, gentle airflow, and no nutrients — it’s feeding off the cotyledons and the soil. Start a quarter-strength feed only once the cotyledons yellow and there are two or three sets of true leaves. The whole stage’s threats are too much water (drown/damping off), too much light (scorch), too much food (burn), and too much fidgeting.

What does normal look like — and what doesn’t?

Normal: slow, steady, a new set of leaves every several days, even green, a stem that firms up with a bit of airflow. Trouble: a tall, thin seedling leaning over (stretch — light too far, lower it and support the stem); a droopy seedling in dark wet soil with a thin translucent stem base (overwatering heading to damping off — less water, more air); curling or bleaching nearest the light (too close — raise it). The single best thing you can do for a healthy-looking seedling is nothing — check it once a day and walk away. The plant doesn’t need your help in these two weeks; it needs you to stop helping.

FAQ

How long is the cannabis seedling stage? About two to three weeks — from the sprout breaking the surface to a young plant with three or four sets of true leaves, when it transitions into vegetative growth.

Should I feed a seedling? Not for the first couple of weeks. It lives off the seed’s stored energy and the soil. Begin at quarter strength only when the cotyledons yellow and a few sets of true leaves have formed.

Why is my seedling tall and thin? It’s stretching for light that’s too far or too weak. Lower the light, support the stem with soil or a stake, and it will thicken up as it gets enough light.

More like this