Before diagnosing ANY nutrient deficiency, check your pH. Most "deficiencies" are actually pH lockout — nutrients are present but unavailable.
of diagnosed "deficiencies" are actually pH lockout
pH lockout looks IDENTICAL to deficiencies. Don't diagnose without checking pH first.
Yellowing, spots, curling, discoloration on leaves
Water until 10-20% runoff. Test the runoff pH immediately.
Check pH of your nutrient solution BEFORE feeding.
Soil: 6.0-6.8
Hydro/Coco: 5.5-6.2
Adjust pH with pH Up/Down. Flush if severely off. Wait 3-5 days. Symptoms will improve.
If pH is in range and symptoms persist, THEN diagnose deficiency below.
Adding more nutrients to a pH-locked plant makes things WORSE. You'll overdose the plant while it still can't absorb what it needs. Check pH first. Always.
WHERE symptoms show tells you WHAT'S wrong. This is the most important diagnostic concept.
What "mobile" means: The plant CAN move these nutrients from old leaves to new growth. When deficient, it "cannibalize" older leaves to feed new growth.
What "immobile" means: The plant CANNOT move these nutrients once they're locked into tissue. Deficiency shows on NEW growth because the plant can't redistribute from old leaves.
Looks like: Yellowing/bleaching on top leaves closest to light. Fix: Raise lights, reduce intensity.
Looks like: Leaves curling upward ("taco-ing"), crispy edges. Fix: Lower temps, increase airflow.
Looks like: Droopy leaves, yellowing, slow growth. Fix: Let soil dry out, check drainage.
Looks like: Purple stems/leaves, slow growth. Fix: Increase room/root zone temp (65°F+ roots).
Detailed symptom descriptions, causes, pH lockout ranges, and Toledo-approved fixes
Lower leaves turn uniformly pale yellow, starting from the tips and progressing upward through the plant. The yellowing is EVEN across the entire leaf (not splotchy). Leaves eventually turn completely yellow, then tan/brown, and fall off. Plant growth slows dramatically. Stems may become thin and weak. In severe cases, the ENTIRE plant becomes pale green/yellow.
OLD GROWTH FIRST (bottom leaves), progresses upward. Mobile nutrient.
Underfeeding, pH too high (>7.0), cold root zone (<60°F), flushing too early
Locks out below 5.5 or above 7.5 — Most available 6.0-7.0
Any base veg nutrient: Athena Core + Grow, Fox Farm Grow Big, GH Flora Gro + Micro, Jack's 3-2-1, Advanced Nutrients Sensi Grow, Botanicare Pure Blend Pro Grow
Dark blue-green or purple leaves, especially on stems and undersides of leaves. Lower leaves may develop dark purple/brown spots. Growth becomes severely stunted — plants look small and compact. Leaves are small, thick, and dark. Flowering is delayed and yields suffer. Stems often turn purple/red (but note: some strains naturally have purple stems). Cold temps can trigger false P-deficiency appearance.
OLD GROWTH FIRST (lower leaves), but affects entire plant growth. Mobile nutrient.
pH too high (>7.0) or too low (<5.5), cold temps (<60°F), overwatering (wet roots block P)
VERY pH sensitive: locks out below 5.5 AND above 7.0 — Optimal 6.0-6.5
Bloom boosters: Athena PK, Fox Farm Tiger Bloom, GH Flora Bloom, Heavy 16 Fire, Grotek Monster Bloom, Botanicare Hydroplex
Brown, burnt-looking edges on older leaves (called "marginal necrosis"). The leaf edges turn brown and crispy while the center stays green. Leaves may curl upward at the edges. Brown spots can appear between veins. Stems become weak and brittle. Buds develop slowly and stay small. Plants are more vulnerable to heat stress and disease. Often appears in mid-to-late flower when K demand is highest.
OLD GROWTH FIRST (lower/middle leaves). Mobile nutrient. Common in flowering.
Underfeeding in flower (high K demand), salt buildup blocking uptake, pH below 5.0 or above 7.0
Locks out below 5.0 or above 7.0 — Most available 6.0-7.0
Bloom nutrients (high K): Any bloom-phase nutrient line (Fox Farm Tiger Bloom, GH Flora Bloom, Athena Bloom, Advanced Nutrients Big Bud), Botanicare Hydroplex, Grotek Monster Bloom
Brown or tan spots on NEW growth (tops of plant). New leaves come in crinkled, twisted, or cupped. Leaf tips and edges die back (necrosis). Growing tips may die completely ("tip die-back"). Stems are weak and hollow. Roots are stunted and brown. Bud development suffers — buds are loose and airy. Very common in coco coir (coco naturally binds calcium) and when using RO water (no minerals).
NEW GROWTH (top of plant). Immobile nutrient — can't move Ca from old leaves.
pH too low (<6.0 in soil, <5.5 hydro), RO water without cal-mag, coco coir (binds Ca), low humidity
Locks out below 6.0 in soil, below 5.5 in hydro — Optimal 6.2-6.8
Cal-Mag supplements: General Hydroponics CaliMagic, Botanicare Cal-Mag Plus, Athena Core (has Ca built in), Jack's Calcium Nitrate
Interveinal chlorosis on OLDER leaves — the tissue between the veins turns yellow while the veins stay green (looks like a yellow leaf with green "highways"). Starts on lower/older leaves and moves upward. Yellowing progresses from the edges inward. Leaf tips may curl upward. In severe cases, yellow areas turn brown and necrotic. Very common in coco coir. Distinguished from iron deficiency because Mg starts on OLD leaves (Fe starts on NEW leaves).
OLD GROWTH FIRST (lower leaves). Mobile nutrient. Interveinal chlorosis (yellow between veins).
pH too low (<5.8), coco coir (binds Mg), excess potassium competing for uptake, RO water
Locks out below 5.8 — Most available 6.0-7.0
Magnesium sources: Epsom salt (magnesium sulfate), Cal-Mag supplements (CaliMagic, Cal-Mag Plus), Botanicare Silica Blast (has Mg)
Uniform yellowing of NEW growth — the entire new leaf turns pale yellow/lime green (not just between veins). Looks similar to nitrogen deficiency BUT starts on NEW leaves instead of old. Stems may turn purple/red. Growth slows. Leaves are small and thin. VERY RARE — most base nutrients contain adequate sulfur. Only seen with extremely low-quality water or in advanced hydro setups using pure salts.
NEW GROWTH (semi-mobile, but shows on new leaves). Rare deficiency.
Extremely rare — usually pH related, or using incomplete base nutrients. Almost never sulfur itself.
Locks out below 5.5 or above 7.5 — Most available 6.0-7.0
Any complete base nutrient contains sulfur. If truly needed: Epsom salt (magnesium sulfate).
Bright yellow or white NEW growth with GREEN VEINS (interveinal chlorosis on new leaves). New leaves come in pale yellow, almost white in severe cases. The veins stay green while the tissue between turns yellow/white. Starts at the TOP of the plant (new growth). Leaves are thin and stunted. Distinguished from magnesium deficiency because Fe shows on NEW leaves (Mg shows on OLD leaves). Almost always caused by pH too high — iron is the FIRST nutrient to lock out as pH rises above 6.5.
NEW GROWTH FIRST (top of plant). Immobile nutrient. Interveinal chlorosis on NEW leaves.
pH TOO HIGH (>6.5 hydro, >7.0 soil) is the #1 cause. Iron is EXTREMELY pH sensitive.
FIRST nutrient to lock out as pH rises. Locks above 6.5 hydro, 7.0 soil. Optimal 5.5-6.2
Iron sources: General Hydroponics Flora Micro (contains chelated Fe), most complete base nutrients contain iron. Fix pH FIRST before adding supplements.
Interveinal chlorosis on new-to-mid leaves (veins green, tissue yellow), with tan or brown spots appearing in the yellowed areas. Looks similar to iron deficiency but with necrotic (dead brown) spots. New growth is pale. Leaves may curl or crinkle. Less common than iron deficiency but has similar causes (high pH).
NEW-MID GROWTH. Immobile nutrient. Interveinal chlorosis + brown spots.
High pH (>6.5), overwatering (wet soil blocks Mn), excess iron competing
Locks out above 6.5 — Most available 5.0-6.5
Complete base nutrients (GH Flora Micro, Athena Core, etc.) contain manganese. Fix pH first.
New leaves are small, twisted, and distorted. Interveinal chlorosis (yellow between veins) on new growth. Leaf tips and edges die back. Leaves grow in thick and crinkled. Internodal spacing decreases (nodes bunch together). Stems are thin. Growth is severely stunted. Rare but devastating when it occurs.
NEW GROWTH. Immobile nutrient. Small, twisted new leaves.
High pH (>6.5), excess phosphorus competing for uptake (too much bloom booster)
Locks out above 6.5 — Most available 5.0-6.5
Complete base nutrients contain zinc. Fix pH first, reduce excessive bloom boosters.
Wilting of new growth despite adequate watering. New leaves are dark blue-green and shiny. Leaf tips and margins turn brown. Growth is slow and stunted. Stems are weak. EXTREMELY RARE — almost never seen in normal growing. Usually only occurs with very high pH or use of reverse osmosis water with incomplete nutrients.
NEW GROWTH. Immobile nutrient. VERY RARE deficiency.
High pH (>7.0), using incomplete nutrients, extremely rare in normal growing
Locks out above 6.5 — Most available 5.0-6.5
Any complete base nutrient (GH Flora Micro, Athena, etc.) contains copper. Check pH first.
Thick, brittle, or hollow stems. Growing tips die back and turn brown. New growth is distorted, twisted, or burnt-looking. Leaves are thick and curled. Root tips die back (brown roots). Stems crack or split. Very rare deficiency. Often triggered by drought stress (not enough water).
NEW GROWTH (stems and tips). Immobile nutrient. Rare.
Drought stress (underwatering), high pH (>7.0), very rare in normal conditions
Locks out above 7.0 — Most available 5.0-7.0
Complete base nutrients contain boron. Ensure proper watering and pH.
Interveinal chlorosis on mid-plant leaves (yellow between veins). Leaf edges curl upward. Leaves may turn pink or orange in severe cases. Looks similar to nitrogen deficiency but shows on middle leaves. Rare deficiency. Unique trait: Mo is the ONLY nutrient that locks out from LOW pH (opposite of most nutrients).
MID-PLANT leaves. Semi-mobile nutrient. Rare.
LOW pH (<5.5) — opposite of most nutrients! Mo needs higher pH to be available.
Locks out BELOW 5.5 — Most available 6.0-7.0 (unique: needs HIGHER pH)
Complete base nutrients contain molybdenum. Raise pH if below 5.5.
Overfeeding is MORE common than deficiencies. Know the signs of toxicity.
Dark green, shiny leaves that "claw" downward (tips curl down like eagle talons). Leaves are thick and leathery. Growth is lush but stems are weak. Flowering is delayed. Buds don't develop properly (too much N in flower = poor yields). Leaves are brittle and snap easily.
Overfeeding veg nutrients, using veg nutes in flower, "hot" soil (Fox Farm Ocean Forest), not tapering N in late flower
Reduce nitrogen immediately. Switch to bloom nutrients (low N, high PK). Flush with plain water if severe. Lower base nutrient dosage. In flower, keep N minimal.
Brown, crispy leaf tips on ALL leaves (top, middle, bottom). Tips look burnt. Progresses to edges if severe. Leaves curl down or up at tips. EC/PPM runoff is much higher than input. Very common in flower when pushing nutrients hard.
Overfeeding (too high EC/PPM), salt buildup in medium, not enough runoff (salts accumulate)
Reduce nutrient strength by 25-50%. Flush with plain pH'd water (1-2x pot volume). Ensure 10-20% runoff with every feed. Lower EC/PPM targets. "Less is more" — slight underfeeding is safer than overfeeding.
Rare. Locks out zinc, iron, and copper. Symptoms: zinc/iron deficiency on new growth despite good pH. Cause: Excessive bloom boosters. Fix: Reduce PK supplements.
Uncommon. Locks out calcium and magnesium. Symptoms: Ca/Mg deficiency on new growth. Cause: Excessive bloom boosters. Fix: Reduce K, increase cal-mag.
Usually from pH too LOW. When pH drops below 5.0, iron, manganese, and copper become TOO available → toxicity. Symptoms: Brown spots, burnt tips, rust-colored leaves. Fix: RAISE pH to 5.8-6.2.
"Less is more" with nutrients. It's easier to add more than to fix overfeeding. Start at 50-75% of recommended dosages. Work up slowly. Monitor runoff EC/PPM. Ensure 10-20% runoff every feed to prevent salt buildup. Most "deficiencies" are either pH or overfeed/lockout.
Answer these questions to identify the problem (after checking pH first!)
⚠️ REMINDER: Check pH first! This diagnosis assumes pH is correct (5.8-6.2 hydro, 6.0-6.8 soil)
All nutrients at a glance — print this for your grow room
| Nutrient | Mobility | Key Symptom | Where Shows | pH Lockout | Common Fix | Severity |
|---|---|---|---|---|---|---|
| Nitrogen (N) | Mobile | Uniform yellowing | Old leaves | <5.5 or >7.5 | Increase base nutes | COMMON |
| Phosphorus (P) | Mobile | Purple stems, dark leaves | Old leaves | <5.5 or >7.0 | Fix pH, warm temps | COMMON |
| Potassium (K) | Mobile | Brown burnt edges | Old leaves | <5.0 or >7.0 | Bloom nutes, flush salts | COMMON |
| Calcium (Ca) | Immobile | Brown spots, crinkled new leaves | New growth | <6.0 (soil) <5.5 (hydro) | Cal-mag, raise pH | COMMON |
| Magnesium (Mg) | Mobile | Interveinal chlorosis (veins green) | Old leaves | <5.8 | Epsom salt, cal-mag | COMMON |
| Sulfur (S) | Immobile | New growth yellow (uniform) | New leaves | <5.5 or >7.5 | Check pH (rarely true S def) | RARE |
| Iron (Fe) | Immobile | Yellow new leaves, green veins | New growth | >6.5 (very sensitive) | LOWER pH immediately | COMMON |
| Manganese (Mn) | Immobile | Yellow + brown spots, new growth | New-mid leaves | >6.5 | Lower pH, drainage | UNCOMMON |
| Zinc (Zn) | Immobile | Small, twisted new leaves | New growth | >6.5 | Lower pH, reduce P | UNCOMMON |
| Copper (Cu) | Immobile | Wilting new growth | New growth | >6.5 | Check pH | RARE |
| Boron (B) | Immobile | Thick stems, distorted tips | Stems, new tips | >7.0 | pH, proper watering | RARE |
| Molybdenum (Mo) | Mobile | Mid-leaf yellowing, edges curl up | Mid-plant | <5.5 (needs HIGH pH!) | RAISE pH | RARE |
Each nutrient has an optimal pH range. Outside this range = lockout even if nutrients are present.
6.0 - 6.8
Optimal: 6.3-6.5
5.5 - 6.2
Optimal: 5.8-6.0
"If multiple deficiencies appear simultaneously, it's almost certainly pH lockout, not multiple nutrient problems."
Seeing yellowing, spots, AND burnt tips all at once? Don't add 5 different supplements. Check your pH. Fix that first. Give it 3-5 days. Most problems resolve when pH is corrected.
Bring a leaf sample to our Toledo store for FREE diagnosis from our expert growers.