Health Library

Nitrogen deficiency is the most common nutrient issue you'll run into. Because nitrogen is mobile, the plant pulls it from older lower leaves to feed new growth — so you'll always see symptoms starting at the bottom and working their way up. Affected leaves fade to a uniform pale yellow (tips first, spreading inward across the whole blade). Unlike magnesium deficiency, the yellowing is even across the leaf — veins and tissue all turn yellow together. It's most common during rapid veg growth when demand spikes, or when plants are root-bound or overwatered. Some yellowing of lower leaves during late flowering is completely normal as the plant redirects energy to buds — don't overcorrect it.

Potassium deficiency is one of the easier problems to identify — look for brown, crispy leaf edges on the lower leaves while the veins stay green. It's a mobile nutrient, so the plant robs older leaves first. Yellowing starts at the leaf margins and tips, then works inward toward the midrib with a blotchy, patchy pattern (not the smooth uniform fade you'd see with nitrogen). Stems and petioles may turn reddish. Plants often show increased stretching between nodes early on, then stunted growth as it worsens. K deficiency tanks disease resistance and makes plants vulnerable to drought. Common causes: pH above 8.0 in soil (7.5 in coco, 7.1 in hydro), excess calcium or nitrogen locking out K, overwatering, salt buildup, or cold root zones. Demand surges hard during flowering weeks 3–7.

Magnesium deficiency is one of the most common issues, especially in coco coir or under LED lights (LEDs produce less infrared heat, reducing transpiration and passive Mg uptake). As a mobile nutrient, the plant pulls Mg from older leaves to feed new growth — so symptoms always start at the bottom. The telltale sign is interveinal chlorosis: the tissue between veins turns yellow while the veins themselves stay dark green, creating a distinctive green-vein network overlaid on yellow tissue. The yellowing has a soft, cloudy quality and spreads inward from the leaf margins toward the central vein. It often worsens during flowering as developing buds act like a nutrient sink, pulling magnesium from leaves. Cold root zones below 64°F (18°C) also reduce Mg absorption significantly.

Molybdenum deficiency is rare but sneaky — the plant has plenty of nitrogen available, yet can't use it. Without Mo, the enzyme that converts nitrate to usable ammonium doesn't work, so symptoms mimic N deficiency even with adequate feeding. Unlike other mobile nutrients that show symptoms at the very bottom, Mo uniquely starts at mid-canopy leaves and spreads upward — this is the key way to tell it apart from nitrogen deficiency. Look for yellowing at the leaf margins (not between veins like Mg) with distinctive orange, pink, or red tints at the edges. Usually caused by acidic pH — a root zone drifting below its target (6.3 in soil, 5.8 in coco, 5.5 in hydro) — or cold root zone temperatures.

Wind burn happens when leaves take a constant direct blast from a fan -- excessive wind accelerates transpiration, meaning water evaporates from the leaf surface faster than the plant can replace it, causing localized dehydration. You'll see curling, clawing, and dry-looking foliage, but only on leaves in the direct path of airflow. Air circulation is essential, but leaves need a gentle intermittent breeze, not a nonstop jet aimed right at them. Wind burn is often confused with nitrogen toxicity because both cause clawing -- but wind burn only affects fan-exposed leaves while nitrogen toxicity affects the entire plant with dark green, waxy foliage.

Nutrient burn is one of the most common problems in cannabis growing — it's general salt toxicity from a nutrient solution that's too concentrated or from salts accumulating in the medium over time. The very tips of leaves yellow, then brown and crisp up, and unlike light burn (which hits the canopy tops) or single-element deficiencies (which target specific leaf zones), nute burn affects leaves throughout the entire plant simultaneously. It's especially common with synthetic fertilizers and in coco or hydro setups where salts build up fast. It often co-occurs with nitrogen toxicity — if you're seeing dark green clawing leaves AND burnt tips, you're likely overfeeding across the board. Seedlings in "hot" soil (fresh compost or amended super-soil) can show burn within days. A slight tip burn is actually considered acceptable by many experienced growers as a sign you're feeding near max, but any progression beyond the very tips means you need to back off. Damaged tissue won't recover — you're watching for healthy new growth as the sign things are improving.