Seedling stalled for over a week

Likely causes, most likely first

Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.

1. PossibleOverwatering (roots short of air)

   Root zoneDeal with it this weekRead: Drooping cannabis: overwatering vs underwatering

   Fix: Water only when the pot is clearly lighter (about half the water used), then water to 10-20% runoff. Seedlings in big pots: water a small ring near the stem only. Add air: fabric pots, 25-40% perlite, no saucer standing water. Let a soaked pot dry back before the next watering.

   Recovery: Leaves lift within a day of drying back; colour and growth recover within 5-7 days.

   How to confirm it

   • Lift the pot and check moisture at depth. Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst.
   • Look at the roots. Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
   • Smell test of roots, medium and reservoir. Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case.

2. PossibleAutoflower stunted by early stress

   EnvironmentDeal with it this weekRead: Why is my autoflower so small?

   Fix: Autos run on a countdown from germination, so lost growth never returns. Next run: sow straight into the final 11-19 L (3-5 gal) pot, never transplant, water seedlings in small rings, give 300-600+ µmol/m²/s early, train with LST only (topping never matches proper LST). This run: keep conditions steady and feed well; don't add more stress.

   Recovery: Steady weekly growth from here on; size gap to siblings stops widening.

   How to confirm it

   • Lift the pot and check moisture at depth. Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst.
   • Measure PPFD at the canopy top. Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little.

3. Less likelyFungus gnats

   PestLow urgencyRead: Fungus gnats: the watering problem with wings

   Fix: Fix the watering first: let the top 2-3 cm dry. Then Bti drenches (larvicide), Steinernema feltiae nematodes or Stratiolaelaps mites; yellow cards for adults. Larvae chew seedling and clone roots and can open the door to Pythium.

   Recovery: Card catches fall within 2-3 weeks; no larvae under potato slices.

   How to confirm it

   • Sticky cards for 1-2 weeks. Hang yellow cards at canopy height and lay one flat on the medium surface; add blue cards for thrips. Count catches every 3-4 days. Rising counts of small dark flies at the medium mean fungus gnats; slender insects mean thrips; white wedge-shaped fliers mean whiteflies; winged aphids mean a colony nearby.
   • Potato slice test for larvae in the medium. Press 2-3 raw potato slices (1 cm thick) cut side down onto the medium surface. Lift after 2-4 days and look underneath: translucent larvae with shiny black heads are fungus gnat larvae.

4. Less likelyChlorine or chloramine in tap water harming roots and soil life

   Root zoneLow urgencyRead: Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine

   Fix: Usual tap levels rarely hurt the plant directly; the concern is living soil, beneficial microbes and young roots. Chlorine gasses off in 24 h of aeration; chloramine does not. Remove chloramine with long-contact or catalytic carbon, or about 1 g of ascorbic acid per 100-400 L, or use RO.

   Recovery: Biology recovers over weeks; seedlings resume growth within a week.

   How to confirm it

   • Get a water report (or test your water). Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium.

5. Less likelyDamping-off

   DiseaseAct within a day or twoRead: Damping-off: why seedlings collapse at the soil line

   Fix: A collapsed seedling can't be saved. For the rest: clean containers, fresh mix, warm medium (22-26 °C / 72-79 °F), water lightly, good light and airflow.

   Recovery: No further collapses.

   How to confirm it

   • Lift the pot and check moisture at depth. Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst.

6. Less likelySeed coat stuck on the cotyledons (helmet head)

   Physical damageDeal with it this weekRead: What do I do if the seed shell is stuck on my seedling?

   Fix: Mist the shell to soften it and raise RH around the seedling (dome) for a few hours; if it is still stuck, ease it off gently with clean tweezers. Plant seeds about 0.5-1.5 cm (1/4-1/2 in) deep so the medium scrapes the coat off on the way up.

   Recovery: Cotyledons open within a day.

   How to confirm it

   • Check temperature and RH at canopy height with a calibrated sensor. Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.

Look for

Seedling with its pot, the medium moisture and light distance..