Your plant's health,
explained

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.

Phosphorus deficiency looks different from most other mobile nutrient issues — instead of yellowing, you'll see leaves getting darker. The plant redirects P from older lower leaves to new growth, so symptoms always start at the bottom. Leaves turn an unusually dark green or blue-green, often with purple stems and petioles. This is caused by anthocyanin pigment building up in starving tissue. Cold root zones (below 60°F/15°C), pH issues, or overwatering are the usual triggers. During flowering, P demand surges and deficiency can be devastating — leaves closest to buds and directly under lights often show the worst discoloration.

Iron is immobile, so deficiency always shows up on the newest growth first. This makes it easy to confuse with normal new growth, which is also naturally pale green — but healthy new leaves darken within a few days and are uniformly light, while iron-deficient leaves develop a distinct interveinal pattern and don't resolve on their own. The classic sign is interveinal chlorosis — young leaves turn yellow between the veins while the veins themselves stay dark green. What makes iron unique is that it can progress to nearly white leaves if left unchecked. If you're seeing leaves that are almost bleached white with green veins, that's a near-certain indicator of iron deficiency specifically. Unlike manganese deficiency which develops tan or brown spots between the veins, iron produces no spots at all — just clean yellowing or whitening. Another unusual trait: Fe-deficient leaves can actually recover and re-green from the tips inward once you fix the issue, which is rare for nutrient deficiencies. Browning of leaf tips and edges may develop in later stages. The primary cause is almost always high pH above 6.5, which converts iron into unavailable forms — it's rarely an actual shortage in the medium. Excess zinc, manganese, or copper can also lock out iron through competition, and cold root zones, overwatering, poor drainage, or excess phosphorus all reduce iron availability.

Spider mites are tiny arachnids — not insects — that feed from the undersides of leaves by piercing individual cells and sucking out the contents. Each puncture destroys one cell's worth of chlorophyll, so the damage shows up on the leaf tops as tiny pale speckles called stippling. They thrive in hot, dry conditions and reproduce explosively — a handful of mites can become thousands in under two weeks. Two-spotted spider mites (Tetranychus urticae) are by far the most common species on cannabis. They're usually introduced on clones, clothing, or pets, and they're so small you won't notice them until the stippling gives them away. Don't confuse stippling with thrips damage — mites leave tiny dots in a scattered pattern, while thrips leave silver streaks along the veins. By the time you see webbing between branches, you're dealing with a serious colony that needs immediate action.