Whole plant pale or lime green

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. PossibleGeneral underfeeding (whole feed too weak)

   NutrientDeal with it this weekRead: Building a cannabis feed by stage: ppm targets per element and how to hit them

   Fix: Raise the whole feed in steps of about 0.2-0.3 mS/cm toward the stage target (veg 1.2-1.8, flower 1.6-2.2 mS/cm in coco and hydro). Stop any 'flush': plain water for weeks starves the plant, and pre-harvest flushing is a myth that costs yield.

   Recovery: Colour deepens and growth speeds up within a week; runoff EC tracks input.

   How to confirm it

   • 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.
   • 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.

2. PossibleNitrogen deficiency

   NutrientDeal with it this weekRead: Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets

   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.

   How to confirm it

   • 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.
   • 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.
   • 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.
   • 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.
   • 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.

3. 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.

4. Less likelyTwospotted spider mites

   PestAct within a day or twoRead: Spider mites on cannabis: life tables, ID and IPM

   Fix: Act now: they breed fastest hot and dry. Remove the worst leaves into a sealed bag, cool the room and raise RH a little (in veg), release predatory mites (Phytoseiulus persimilis for hot spots, Neoseiulus californicus as a preventive) before numbers explode. Soaps or horticultural oils only in veg, never on buds. Quarantine new clones.

   Recovery: No new stippling on new leaves and no live mites at 10-20x after 7-14 days.

   How to confirm it

   • Magnifier check of leaf undersides and new growth. Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
   • Tap a branch over white paper. Hold white paper under a branch or bud and tap it sharply 3-4 times. Watch the paper for 30 seconds: moving specks are mites or thrips (smear them; spider mites leave red-brown or green streaks), larger fliers are whiteflies. A quick whole-room screen before the magnifier.

5. Less likelyCold root zone (below about 16 °C / 61 °F)

   Root zoneDeal with it this weekRead: Temperature by stage: day, night and root-zone targets

   Fix: Raise root-zone temperature to 18-22 °C (64-72 °F): lift pots off cold floors onto insulation, warm the room at night, use an aquarium heater in reservoirs (with a thermostat), water with room-temperature solution.

   Recovery: Growth resumes and new leaves green within a week.

   How to confirm it

   • Measure reservoir and root-zone temperature at the end of the light period. Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows.
   • 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 likelyNot enough light

   LightLow urgencyRead: Stretchy, leggy cannabis: a differential

   Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat.

   Recovery: New internodes shorten within a week; denser buds on the following weeks of growth.

   How to confirm it

   • 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.

7. Less likelyRoot-bound in a pot too small

   Root zoneDeal with it this weekRead: Cannabis root problems: the master decision tree

   Fix: Up-pot photoperiods into a container about 2-3x larger, loosening circling roots gently. Autoflowers: don't transplant; increase watering and feeding frequency instead. Small pots can still grow big plants with high-frequency fertigation (several feeds a day).

   Recovery: New white roots in the fresh medium within 5-7 days; daily wilting stops.

   How to confirm it

   • 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.
   • 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.

8. Less likelySulfur deficiency

   NutrientLow urgencyRead: Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources

   Fix: Rare unless a feed is built only from nitrates and chlorides. Supply about 50-120 mg/L S as sulfate, e.g. via magnesium sulfate or potassium sulfate at normal rates.

   Recovery: New leaves emerge green within 7-10 days.

   How to confirm it

   • 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.
   • 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.
   • 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.

Look for

Uniform light-green canopy, no vein pattern, no spots; compare with a healthy plant of the same cultivar..