Health Library

Calcium deficiency shows up as brown or rust-colored spots on new growth, usually alongside distorted or crinkled young leaves. Because calcium is immobile — once it's deposited in cell walls, the plant can't move it — new growth always gets hit first. Typically that means the top of the canopy, though during flowering, symptoms can appear on lower fan leaves first as the plant prioritizes calcium toward developing buds (Gali et al. 2023). The transpiration dependence is what makes calcium tricky: even if your nutrient solution has plenty of Ca, low humidity, cold root zones, or still air can limit delivery. It's extremely common in coco coir (which naturally binds calcium), soft water areas, and RO water setups without supplementation. LED and HID growers often run into calcium issues because intense lighting drives faster growth without necessarily increasing transpiration to match. Unlike magnesium or iron deficiency which show clean interveinal yellowing, calcium produces brown spots combined with structural distortion — twisted leaves, cupped edges, and eventually hollow stems. That hollow stem symptom is unique to calcium and a reliable identifier.

Boron is immobile, so deficiency always shows up in the newest growth first. The plant can reach a decent size, but once growing tips start dying off, flowers and buds fail to develop properly. You'll see thick, twisted shoot tips, brown dead patches on young leaves, and roots that swell, shorten, and become fragile — while stems may hollow out and feel soft. Boron deficiency is uncommon but tends to strike when humidity drops below 25% or during underwatering, because boron travels exclusively in the transpiration stream — if water movement slows, boron delivery stops. High pH (above 7.0 in soil, 6.5 in coco, 6.1 in hydro), sandy soils that leach easily, and excessive flushing can also trigger it. One important differentiator from calcium: with boron, the entire leaf curls downward and stems go soft, whereas calcium deficiency causes just the margins to curl and stems turn brittle. Be very careful with supplementation — boron toxicity kicks in at levels only slightly above optimal, so the margin for error is razor-thin.

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.

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.

Root rot is caused by pathogens — primarily Pythium and Fusarium — that thrive in waterlogged, oxygen-depleted root zones. It's the end result of chronic overwatering, poor drainage, or root zone temperatures above 72F/22C. The key distinction from simple overwatering: overwatered roots are still white and firm (just sitting in too much water), while root rot roots are brown, slimy, and smell terrible. Fungus gnat larvae make things worse — they chew on roots and create entry points for Pythium, so if you're seeing gnats, check for rot too. Seedlings and freshly transplanted plants are especially vulnerable in the first three weeks — they can collapse at the soil line overnight (damping off). In hydro systems, root rot spreads through the reservoir fast and can take out an entire grow. Early intervention is critical because once the root mass is mostly brown and mushy, the plant rarely recovers.

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.