# Seedling leaves (cotyledons) yellowing: likely causes and fixes

> Seedling leaves (cotyledons) yellowing on cannabis is most often Seed leaves yellowing as true leaves take over (normal), Overwatering (roots short of air) or Nitrogen deficiency. How to tell them apart, the fix for each and what recovery looks like.

Also called: seed leaves yellow, round leaves turning yellow, cotyledons dying, seedling first leaves yellow.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=old&s=yellow-cotyledons

## Likely causes, most likely first

### Seed leaves yellowing as true leaves take over (normal) (Likely)

- Kind: Normal ageing; urgency: Low urgency
- Fix: Normal after 2-4 weeks once several true-leaf sets are growing. Early yellowing with wet medium is overwatering; with hot soil it may be over-strong soil.
- Recovery: True leaves keep growing green.
- Confirm: 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.
- Article: [Why are my seedling's leaves yellow or pale?](https://genetixbay.com/knowledge/answers/seedling-leaves-yellow.md)

### Overwatering (roots short of air) (Possible)

- Kind: Root zone; urgency: Deal with it this week
- 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.
- Confirm: 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.
- Confirm: 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.
- Confirm: 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.
- Article: [Drooping cannabis: overwatering vs underwatering](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md)

### Nitrogen deficiency (Less likely)

- Kind: Nutrient; urgency: Deal with it this week
- Fix: Fix roots, watering and pH first. If N is genuinely short, raise feed N by about 10-20% (not double): mineral feeds around 150-200 mg/L N in veg and early flower; one DWC flowering trial predicted a yield optimum near 194 mg/L. Coco/hydro: raise base feed EC by ~0.2 mS/cm. Soil: liquid feed at label rate. Living soil: top-dress a fast organic N source and allow 1-2 weeks. Late flower: a gradual fade is the planned N taper, not a fault.
- Recovery: Yellowing stops climbing within 5-7 days and new leaves emerge mid-green; already-yellow leaves do not recover. Runoff EC climbs back toward input.
- Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.
- Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
- Confirm: 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.
- Confirm: Watch new growth for 5-10 days after one change: Make one correction at a time, mark the top node with a twist tie and photograph the same leaves every 2-3 days. Damaged leaves never recover; judge only new growth and whether the symptom stops spreading. Mobile-nutrient symptoms stop climbing within 5-7 days; immobile ones show in new leaves within 7-10 days.
- Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency.
- Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md)

## Note

Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.