Health Library

Light burn happens when leaves sit too close to your grow light -- whether that's a high-powered LED or a big HPS -- and the intense PAR causes photo-oxidative damage to the tissue. The first thing you'll usually notice is the top leaves 'praying' upward or tacoing before any color change appears, and then the tissue closest to the light starts bleaching yellow-to-white while the rest of the leaf stays green. That's the key differentiator from heat stress: heat stress causes broad curling with browning edges across the canopy but no bleaching, whereas light burn is strictly proximity-based -- only the leaves physically closest to the bulb get hit. It's also different from iron deficiency, which targets new growth regardless of light distance. One easy diagnostic trick: light-burned leaves feel firm and resist plucking, while nitrogen-deficient yellow leaves wilt and practically fall off on their own.

Heat stress occurs when temperatures exceed the plant's comfort zone (above 85°F/30°C), causing leaves to curl upward like tacos or canoes as they try to reduce surface area exposed to heat. The serrated leaf tips are the first part to curl -- you'll notice them lifting before the full taco shape develops. Unlike light burn, which bleaches the tops of leaves, heat stress causes leaf edges to crisp and brown without any bleaching. Low humidity amplifies the damage because the plant loses water through its leaves faster than the roots can replace it -- a VPD imbalance that makes even moderate heat feel extreme. During flowering, heat stress can cause foxtailing (new calyxes stacking on top of each other), reduced potency, and airy buds. Heat stress often accompanies light stress, but the two are diagnostically distinct.

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.

Overwatering is one of the most common mistakes -- and it's not about how much water you give, it's about how often. Your roots need oxygen between waterings, and when the medium stays soggy, they suffocate. The telltale sign? Leaves droop downward but feel firm and heavy -- not limp and papery like underwatering. The soil stays wet for days, roots can't breathe, and root rot often follows. Water thoroughly each time, but let the medium dry out before you water again.

Underwatering causes plants to wilt as cells lose turgor pressure from lack of water. Unlike overwatering where leaves feel firm, underwatered leaves are limp, thin, and papery. The good news is underwatering is easily fixed -- plants typically recover within hours of watering. Chronic underwatering stunts growth and stresses plants, but it's generally less damaging than overwatering.

When your plant shows symptoms of several different deficiencies at the same time -- yellowing lower leaves, spots on new growth, purple stems, stunted tips -- it's almost never multiple separate problems hitting at once. What you're actually looking at is a systemic issue that's blocking the plant from absorbing multiple nutrients. The most common culprit is pH lockout: when your root zone pH drifts outside the usable window (5.5-7.0 for soil, 5.5-6.5 for coco, 5.5-6.1 for hydro), different nutrients become chemically unavailable even though they're sitting in the solution. Other root causes include damaged roots from root rot or chronic overwatering, severe salt buildup in the medium, or toxicity from one nutrient locking out several others. The key diagnostic clue is that symptoms appear in BOTH upper and lower leaves simultaneously -- single deficiencies follow mobility rules (mobile nutrients show in lower leaves, immobile in upper), but when the root system itself is compromised, everything breaks down at once. The worst mistake at this point is adding more nutrients, which piles on more salts and makes the problem worse. Fix the root cause first.