How to read cannabis deficiency symptoms (and what they actually tell you)
A working cannabis nutrient deficiency chart begins with two readings the plant is already giving you: where on the plant the symptom shows, and what the runoff pH says. Most growers reach for a supplement before answering either. Most home grows do not actually need more nutrients. They need a calibrated pH pen and a closer read of the canopy.
Before you add anything to your soil or reservoir, check pH. Cannabis nutrient lockout from incorrect pH is the most common cause of deficiency-shaped symptoms, even when your nutrients are correctly balanced. Soil should be 6.0–7.0. Hydro and coco should be 5.5–6.5. Outside this range, the nutrients are still in the pot but the root cannot pull them in.
Then look at where the problem starts. Mobile nutrients like nitrogen, magnesium, phosphorus, and potassium move from old leaves to new growth, so deficiency symptoms appear on lower fan leaves first. Immobile nutrients like calcium, iron, sulfur, zinc, and boron stay where they were placed, so deficiency shows up in newer leaves that came in after the deficiency started. The leaf gives you two visual signals to read alongside that location: chlorosis (yellow tissue between green veins) and necrosis (brown, dead tissue along tips, edges, or in spots). That single distinction between mobile and immobile bisects the diagnosis space cleanly.
A short cannabis nutrient deficiency chart for the patterns that get confused most often. You may see this kind of reference called a cannabis deficiency leaf chart, marijuana deficiency chart, or weed plant deficiency chart; the diagnostic logic is the same:
| Symptom | Likely cause | Lookalike to rule out |
|---|
| Yellow on old/lower leaves | Nitrogen deficiency | pH lockout, late-flower drawdown |
| Yellow between veins, old leaves | Magnesium deficiency | Spider mite stippling |
| Yellow between veins, new leaves | Iron or manganese deficiency | pH lockout above 6.5 |
| Brown crispy leaf tips | Potassium deficiency | Nutrient burn (high runoff EC) |
| Twisted, brittle new growth | Calcium or zinc deficiency | Broad mites, heat stress |
| Purple or red stems | Phosphorus deficiency (with leaf damage) | Genetic strain trait, cold roots |
The picker above takes those signals and ranks the matches. Stippling that reads as magnesium might also be early spider mite damage; the cannabis pest identifier covers the lookalikes the picker flags as pest causes.
A 2-minute deficiency check before you correct
The point of a quick check is to rule out the cheap explanations before you mix more nutrients. Two minutes once you spot a symptom is enough.
- Read pH-out from the runoff. Soil should be 6.0–7.0; coco/hydro 5.5–6.5. Outside this range, fix pH first and recheck in 24 hours.
- Read EC (or PPM, if your pen reads in parts per million) from the runoff. Above feed-in plus 0.4 mS/cm means salt buildup; flush before you add anything.
- Look at the top of the plant. Crisp, dark-green new growth means the plant is fed; the symptoms are probably mobility-driven (old-leaf deficiencies, expected).
- Look at the bottom of the plant. Uniform yellowing on the lowest fan leaves can be normal in late flower, but mid-veg yellowing is a flag.
- Use a 10x loupe on a stippled leaf. Spider mites and broad mites mimic deficiencies well enough to fool a tired grower at lights-on.
Once those four readings are clear, the picker’s match becomes high-confidence and the fix is simple. Most “deficiencies” stop being deficiencies the moment runoff pH comes back into range.
The usual suspects in cannabis nutrient deficiencies
Eleven conditions cover roughly nine out of ten home-grow nutrient problems. The picker above carries the deep ID and stage-safe fix notes for each. The short context below explains where each one shows up and the symptom that gives it away first.
Why are my cannabis leaves pale or washed out? (nitrogen)
If your plant goes from green to pale green or light yellow overall, especially on older growth, suspect a cannabis nitrogen deficiency. Nitrogen is a mobile nutrient used heavily during the vegetative stage, and the plant scavenges it from old leaves to feed new growth. Look for slowed growth, uniform yellowing of older leaves, and smaller plant size. Reduce nitrogen during the flowering phase to support healthy bud development; some yellowing late in the grow is normal, but mid-veg yellowing is a warning.
Why do my cannabis plants have purple or red stems? (phosphorus)
Red or purple stems can be a natural trait of some strains. If you also see slow growth, dark-green or dying lower leaves, or brown patches, look at phosphorus. It is critical for root strength in early veg and for bud formation in early flower. Phosphorus is mobile, so symptoms begin in older leaves: lower leaves turn dark green, yellow, or get brown patches, with red or purple stems and progressive yellowing as flowering advances.
Why are my leaf tips turning brown or burnt? (potassium)
Brown, crispy leaf tips often indicate a potassium deficiency. Potassium controls how cannabis plants move water and handle environmental stress. Without enough of it, the plant cannot manage moisture effectively, which dries out the leaf tips. You will also see yellowing at the leaf edges, stunted growth, and poor bud development. These signs usually appear during mid to late veg or early flowering, especially when the nutrient mix is too nitrogen-heavy. Crispy tips alone can also be nutrient burn. Check runoff EC before deciding which it is.
Why are my new leaves twisting or curling up? (calcium)
When new growth curls upward, you are usually seeing a cannabis calcium deficiency. Calcium is immobile, so symptoms show up in new growth first. It strengthens cell walls and is essential for healthy structure. Look for browning or spotting on new leaves, upward-curling edges, and weak stems or stunted shoots. Calcium issues are common in coco or hydro setups when not appropriately supplemented.
Why are leaves yellow between the veins? (magnesium and iron)
Yellow between green veins is called interveinal chlorosis, and it has a few possible causes depending on where the chlorosis starts.
On older leaves: likely a cannabis magnesium deficiency (mobile nutrient). The leaf looks like a green skeleton with yellow webbing. Untreated, the chlorosis spreads outward to engulf the leaf.
On newer leaves: likely iron deficiency (immobile). New top leaves come in pale yellow with green veins, and progress toward a bleached white if untreated. Iron deficiency is a pH problem 90% of the time. Reach for the pH meter before the iron supplement.
Manganese deficiency presents similarly to iron, with the addition of brown or tan necrotic spots. All three look alike, so location and pattern are key to the right diagnosis.
Why are my buds small or weak? (sulfur and potassium)
If your plant looks healthy but your buds are small, airy, or underdeveloped, check potassium and sulfur first. Sulfur is part of every terpene and oil pathway, so its deficiency hits aroma and resin alongside bud size. Symptoms of sulfur deficiency: yellow new growth (not old leaves), weak buds, low aroma, reduced oil and terpene production. Sulfur is partially mobile, so signs may appear in newer or middle growth.
Copper and boron deficiencies can also affect bud structure and density. Copper is rare in cannabis home grows but presents as darkened leaves with pale white or yellow tips and incomplete bud formation. Boron is also rare and shows as brittle stems, distorted new growth, and poor flowering, often paired with calcium deficiency.
Why are my leaves deformed or miniature? (zinc)
If your leaves look small, twisted, or oddly narrow, suspect a zinc deficiency. Zinc is essential for cell division and growth. Look for short internodes (tight spacing between branches), small narrow leaves, and yellowing in new growth. Zinc is immobile, so symptoms appear in newer leaves. Like iron, zinc locks out above pH 6.5 in coco and hydro. Test pH first; supplement second.
When everything looks like a deficiency at once: pH lockout
If the picker surfaces multiple deficiencies for the same plant, the cause is almost always pH lockout. The nutrients are present, but the root cannot pull them in at the current pH. Iron, zinc, and manganese lock out first as pH rises above 6.5; calcium, magnesium, and phosphorus lock out as pH drops below 6.0.
The fix is the same in either direction: correct pH-in (5.8 in coco/hydro, 6.2–6.8 in soil), water-to-runoff at the corrected pH, and recheck in 24 hours. A 0.5-point drift in runoff pH is the early warning before symptoms even appear, which is why measuring runoff pH every feed in coco and hydro is the cheapest preventive habit you can build.
Why a fed plant still burns at the tips: nutrient burn
Brown leaf tips that curl down, paired with leaves clawing (the entire leaf bending down like a hawk’s talon), are the calling card of nutrient burn. Where most of this chart deals with deficiency, nutrient burn is the toxicity end of the deficiency-and-toxicity spectrum. New growth still comes in dark green and glossy because the plant has plenty of nutrients in the root zone. Excess salts there burn the tips and lock out other nutrients secondarily, which is why advanced burn looks like potassium deficiency.
Runoff EC (or PPM) tells you what the plant actually absorbed. Flush with pH-corrected plain water at 1.5–2x pot volume until runoff reads at half the feed-in level, then resume at half the previous strength.
How to fix nutrient deficiencies in cannabis
The picker covers stage-specific fixes per record, but the order of operations is the same across the board.
- Check pH first. Soil 6.0–7.0. Hydro or coco 5.5–6.5. Outside this range is lockout.
- Check runoff EC. Above feed-in EC means salt buildup; flush before correcting anything.
- Use complete cannabis-specific nutrients. A complete base already balances macronutrients (NPK: nitrogen, phosphorus, potassium), secondaries (calcium, magnesium, sulfur), and most micronutrients (iron, zinc, manganese, boron, copper).
- Follow stage-specific ratios. Veg 3-1-1 (high N), early flower 1-3-2 (high P), late flower 0-3-3 (low N, high PK).
- Run Cal-Mag in coco and hydro. Coco binds calcium against the root and reverse-osmosis water arrives without it. Cal-Mag every feed, every grow.
- Flush if you over-fed. Excess of one nutrient blocks others. A pH-corrected water flush at 1.5–2x pot volume resets the salt level.
Why your medium matters
The same plant in three different mediums has three different deficiency profiles.
In soil, the medium buffers pH and stores secondary nutrients across the first 4–6 weeks. Quality soil mixes rarely run out of calcium, magnesium, or sulfur during that window. After week six the buffer depletes and supplementation becomes necessary. The most common soil deficiency is nitrogen, and the most common soil “deficiency” is actually pH lockout below 6.0.
Coco binds calcium and magnesium against the root, so Cal-Mag stops being a supplement and becomes the default feed: every feed, every grow. The first time growing in coco guide covers the buffering routine and the pH-in target that keeps coco from going stale. Coco growers also see overwatering masquerade as deficiency. Droopy leaves with yellowing can be a watering issue first, and the overwatering in coco guide walks through the diagnostic.
Hydro has no buffer at all. pH drift in a reservoir locks iron out before any other nutrient, and a single skipped Cal-Mag dose during heavy feed weeks shows up on the canopy in 48 hours. Hydro growers should check pH twice daily during heavy feed and never let the reservoir drift more than 0.3 points without a correction.
Environment also primes uptake. Transpiration pulls calcium and magnesium up the xylem; kill transpiration and you get Cal-Mag deficiency symptoms that look nothing like a feed problem. The cannabis VPD chart covers the temperature and humidity targets that keep transpiration moving and uptake on schedule.
FAQs
Why are my cannabis leaves turning yellow?
Yellowing on old/lower leaves is usually nitrogen deficiency. Yellowing on new growth is usually sulfur, iron, or pH lockout. Yellow between green veins on old leaves is magnesium; on new leaves it’s iron or manganese. Check pH first. Most yellowing is lockout, not actual deficiency.
How do I fix yellow leaves on cannabis?
Test runoff pH and runoff EC before adding anything. If pH is out of range (below 6.0 or above 7.0 in soil; below 5.5 or above 6.5 in coco and hydro), correct pH and flush. If pH is in range, identify which leaves are yellow first. Old-leaf yellowing means nitrogen, magnesium, phosphorus, or potassium. New-growth yellowing means sulfur, iron, calcium, or zinc. Match the picker output above to a stage-safe fix.
How do I tell calcium from magnesium deficiency?
Location. Calcium is immobile, so it appears on new growth (top of plant) as twisted leaves, brown spots, and weak stems. Magnesium is mobile, so it appears on old growth (bottom of plant) as interveinal yellowing (yellow between green veins). Cal-Mag supplements address both, which is why most coco and hydro growers run them together.
Is it a deficiency or pH lockout?
If multiple deficiencies seem to appear at once, it is almost always pH lockout. Test runoff pH. Soil should read 6.0–7.0; coco and hydro 5.5–6.5. If it is outside that range, fix pH and recheck in 24 hours before adding any supplement.
How do I correct cannabis nutrient lockout?
Adjust pH-in to the medium target (5.8 in coco/hydro; 6.2 in soil for low lockout, 6.8 in soil for high lockout) and water to runoff at the corrected pH. In hydro, dump and refill the reservoir with a pH-correct mix instead of trying to drift it. Recheck runoff pH and EC in 24 hours; if it has come back into range, resume normal feeding at full strength. Calibrate the pH pen monthly with fresh 7.0 and 4.0 buffers; a drifting pen is the most common cause of stealth lockout.
What’s the difference between deficiency and toxicity?
Deficiency is too little of a nutrient; toxicity is too much. Deficiency starts with chlorosis (yellowing, often in a specific leaf-position pattern). Toxicity starts with necrosis at the leaf tips and edges, plus leaf clawing, and runoff EC reads high. The fix is opposite: deficiency wants a feed correction; toxicity wants a flush. The picker treats nutrient burn as the toxicity counterpart in this cannabis deficiency and toxicity chart.
Can pests look like nutrient deficiencies?
Yes, and frequently. Spider mite stippling reads as magnesium deficiency. Broad mites cause twisted new growth that looks like calcium or zinc. Pale upper leaves can be russet mites. The cannabis pest identifier covers the lookalikes; check it before any spray.
What does cal-mag deficiency look like in coco?
Calcium deficiency presents as twisted new growth with brown spots; magnesium as interveinal yellowing on old leaves. Both are common in coco because coco binds calcium and magnesium against the root. The fix is Cal-Mag at full label strength, every feed, every grow.
Should I flush before harvest?
A short flush in late flower (a single water-only feed at 1.5x pot volume) helps drop residual salts, but heavy multi-day flushes stress the plant and contribute to late-flower deficiency symptoms. Drop EC by 25% in the final week instead of cutting nutrients entirely.
What to do next
Most home deficiencies trace back to two upstream issues: a pH pen that has not been calibrated this month, and an under-supplemented coco or hydro feed. The nutrients primer covers what each nutrient actually does in the plant, which is the missing context that turns symptom-matching into diagnosis. If you are setting up your first run, 13 mistakes that ruin a first cannabis grow covers the nutrient and pH patterns that cause most beginner deficiencies.
Don’t chase symptoms without checking the root cause. Many deficiencies look alike, and sometimes the cause isn’t a deficiency at all but a pH issue, poor watering habits, or heat stress. Keep a grow journal, monitor your inputs, and trust the runoff numbers over the bottle. Treat this cannabis nutrient deficiency guide as a bookmarkable cannabis nutrient deficiency app: the picker above stays loaded, so pull it up the next time something on a leaf looks wrong, narrow with the chips, and confirm with a pH meter before you correct.
