Nutrient deficiencies all show in the leaves, but each nutrient leaves a different signature — and the signature, not the colour alone, is what identifies it. Two clues do most of the work: which leaves are affected (old or new) and the pattern (whole leaf, between the veins, or along the margins). Before you reach for fertiliser, though, know that in pots most apparent deficiencies are really uptake problems — the nutrient is present but the roots cannot get it.
The short answer
Old leaves affected first means a mobile nutrient (nitrogen, phosphorus, potassium, magnesium) that the plant is relocating to new growth. New leaves affected first means an immobile nutrient (iron, manganese, calcium, sulphur, boron) that cannot be moved once deposited. That single old-vs-new rule points you at the right half of the list before you look at anything else.
Deficiencies on the OLD (lower) leaves
- Nitrogen (N) — uniform pale green to yellow starting on the oldest leaves; weak, slow, spindly growth. The most common deficiency.
- Magnesium (Mg) — yellowing between the veins of older leaves while the veins stay green (interveinal chlorosis), often with reddish or brown tints.
- Potassium (K) — scorched, browning margins and tips on older leaves, sometimes with yellow mottling; weak stems.
- Phosphorus (P) — dull, dark green leaves, sometimes purple or bronze tints, and stunted growth; hardest to judge by eye.
Deficiencies on the NEW (upper) leaves
- Iron (Fe) — striking interveinal yellowing of the youngest leaves with a fine green vein network; classic on acid-lovers in alkaline soil or hard water.
- Manganese (Mn) — similar interveinal yellowing on new growth but usually with a broader green band along the veins.
- Calcium (Ca) — distorted, hooked or scorched new growth and growing tips; shows in fruit as blossom-end rot on tomatoes and peppers.
- Sulphur (S) — overall pale new growth, resembling nitrogen shortage but on the newest leaves.
How to confirm it really is a deficiency
This is the step most people skip. In containers, true soil-level shortages are less common than uptake failures that mimic them: waterlogged or rotting roots cannot absorb nutrients (see root rot and overwatering vs underwatering); the wrong soil pH locks nutrients out even when they are present (iron becomes unavailable in alkaline conditions, which is why the fix for iron chlorosis is often acidifying the soil, not adding iron); and a root-bound or exhausted mix simply has nothing left to give. Rule these out first — check soil moisture, root health and how long since repotting — before assuming the fertiliser is at fault.
What to do
If roots, water and pH are sound and the pattern still points to a shortage, feed to correct it: a balanced fertiliser resolves nitrogen and general shortages, while specific problems (magnesium, iron) respond to targeted treatments such as Epsom salts for magnesium or a chelated iron/ericaceous feed for iron chlorosis. Follow the product’s own rates — do not guess or over-apply, as excess feeding burns roots and can itself cause marginal leaf scorch that looks like potassium deficiency. Correcting soil pH is often more effective than adding more of a locked-out nutrient. See how and when to fertilize and choosing the right soil.
What not to do, and prevention
Do not treat every yellow leaf as hunger and pile on fertiliser — overfeeding is as damaging as starvation and is a common cause of scorched, salt-burned foliage. Prevent deficiencies with a good potting mix, refreshing or repotting every year or two, moderate regular feeding during the growing season only, watering that keeps roots healthy, and matching acid-loving plants to acidic mix and soft water. Remember that already-affected leaves rarely recover their colour; judge success by healthy new growth.
Plant-group exceptions
Acid-lovers (blueberry, azalea, gardenia, citrus, camellia) show iron and manganese chlorosis readily in hard water or limey soil — the answer is acidification, not more iron. Fast, hungry crops (tomatoes, squash, corn, brassicas) show nitrogen shortage quickly under heavy cropping. Tomatoes and peppers get calcium-linked blossom-end rot mainly from irregular watering that interrupts calcium uptake, not from a lack of calcium in the soil. Related: yellow leaves.
Quick pattern key
- Whole old leaves pale/yellow, weak growth → nitrogen.
- Interveinal yellowing on OLD leaves, green veins → magnesium.
- Scorched margins/tips on OLD leaves → potassium.
- Interveinal yellowing on NEW leaves, green vein network → iron (check pH/roots first).
- Distorted, hooked or scorched NEW growth; blossom-end rot on fruit → calcium (usually a watering-uptake issue).
- Dull dark or purple-tinged leaves, stunted → phosphorus.
Why the mobile/immobile rule works
The old-leaf/new-leaf split is not a memory trick — it reflects plant biology. When a nutrient is in short supply, a plant will cannibalise it from wherever it can be moved. Mobile nutrients (nitrogen, phosphorus, potassium, magnesium) are withdrawn from the old leaves and shipped to the growing tips, so the old leaves show the shortage. Immobile nutrients (iron, calcium, manganese, boron) are locked in place once deposited and cannot be relocated, so a shortage appears in the new leaves that formed after supply ran short. Reading which end of the plant is suffering therefore tells you which group of nutrients to consider before you look at anything else.
When to test rather than guess
Leaf-pattern diagnosis narrows the field, but symptoms overlap and several nutrients can be short at once. For a valuable crop or a persistent problem, a soil test removes the guesswork — and importantly reports pH, which decides whether nutrients that are present can actually be taken up. Adjusting pH into the plant’s preferred range often cures a “deficiency” without adding any fertiliser at all. See choosing the right soil.
Related plant problems
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