Nutrient deficiencies: visual ID by leaf symptom

Visual diagnosis of nutrient deficiencies is one of the more practical skills in horticulture -- if you understand two biological principles, you can narrow most deficiency diagnoses rapidly without laboratory.

—- title: "Nutrient deficiencies: visual ID by leaf symptom" slug: how-to-identify-nutrient-deficiencies hub: problems category: "Identification guide" description: "Diagnose nutrient deficiencies in plants by leaf color pattern and symptom location. Covers nitrogen, phosphorus, potassium, calcium, magnesium, iron, and manganese deficiencies." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-

Visual diagnosis of nutrient deficiencies is one of the more practical skills in horticulture — if you understand two biological principles, you can narrow most deficiency diagnoses rapidly without laboratory testing.

The two principles: (1) Mobility — some nutrients move within the plant from old to new growth; others don't. (2) Pattern — each nutrient causes a characteristic distribution of symptoms on the leaf (whole leaf yellowing vs. interveinal chlorosis vs. marginal burn).

The mobility framework

Per Penn State Extension, nutrients are classified as mobile or immobile within the plant:

Mobile nutrients (move from old to new growth when deficient): N, P, K, Mg, Mo. When these are deficient, the plant relocates them from older, lower leaves to new growth at the shoot tips. Symptoms appear first on older (lower) leaves.

Immobile nutrients (cannot be relocated once deposited): Ca, Fe, Mn, Cu, Zn, B. When deficient, the plant cannot supply enough to new growth from old tissue. Symptoms appear first on new (upper) leaves and young tissue.

This mobility rule is the fastest diagnostic filter.

Nitrogen deficiency (N)

Symptom: Uniform yellowing of older, lower leaves progressing upward. The entire leaf turns yellow (not just between the veins). In severe deficiency, older leaves may die and drop.

Per Penn State Extension, nitrogen deficiency is the most common soil nutrient deficiency in gardens and lawns. It causes general yellowing and pale green color on plants that should be darker green.

Associated conditions: Sandy soils with low organic matter; overwet soils where nitrogen leaches; cool spring soils where microbial N mineralization is slow.

Correction: Apply a nitrogen fertilizer appropriate to the plant type. For lawns: 1 lb actual N per 1,000 sq ft in spring. For vegetables: side-dress with ammonium sulfate or use a balanced vegetable fertilizer per product label.

Phosphorus deficiency (P)

Symptom: Per Penn State Extension, purpling of the undersides of leaves and stems — particularly visible in seedlings growing in cool, wet soil that limits phosphorus uptake. The purple color is from anthocyanin accumulation.

Associated conditions: Cold soil temperatures (below 55°F) temporarily induce phosphorus deficiency in seedlings even when soil P is adequate, because root uptake is temperature-limited. Germinating tomato and corn seedlings in cold spring conditions often show purple undersides that resolve when soil warms.

Correction: Soil test before adding phosphorus — most soils in the eastern US are not phosphorus-deficient with normal management. Cold-weather purpling in seedlings is transient and does not require amendment.

Potassium deficiency (K)

Symptom: Per Penn State Extension, potassium deficiency causes marginal (edge) scorch on older leaves — the leaf margin turns yellow, then brown and dry, while the interior of the leaf stays green. The scorched margin is well-defined.

Associated conditions: Sandy soils with high leaching; soils very high in calcium or magnesium (cation competition interferes with potassium uptake).

Correction: Apply potassium (potassium sulfate, potassium chloride) based on soil test recommendations.

Calcium deficiency (Ca)

Symptom: New growth affected first (immobile). Deformed, crumpled, or distorted new leaves; in vegetables, blossom end rot on tomatoes (dark, sunken base of fruit) is a calcium deficiency symptom in the fruit. Per Penn State Extension, blossom end rot is usually not caused by soil calcium deficiency but by irregular watering that disrupts calcium uptake.

Correction: Most soils have adequate calcium. Blossom end rot is managed with consistent soil moisture, not calcium sprays.

Magnesium deficiency (Mg)

Symptom: Per Penn State Extension, interveinal chlorosis on older leaves — the leaf veins remain green while the tissue between veins turns yellow. The yellowing is in the leaf interior, not at the margins.

Associated conditions: Sandy, acidic soils with high calcium or potassium (magnesium is displaced by competing cations); heavily leached soils.

Correction: Dolomitic limestone (provides both calcium and magnesium) or Epsom salt (magnesium sulfate) applied as a soil drench. Per Penn State Extension, Epsom salt foliar sprays are not a primary correction — soil amendment is needed.

Iron deficiency (Fe)

Symptom: Interveinal chlorosis on new (young) leaves — the veins remain dark green while the tissue between veins turns bright yellow or nearly white. New growth at the shoot tip is the most severely affected. Per Penn State Extension, this pattern is the defining feature of iron deficiency and easily confused with manganese deficiency (see below).

Cause: Iron is abundant in most soils but becomes unavailable to plants at high pH (above 6.5–7.0). Per Penn State Extension, the problem is not soil iron content but soil pH limiting iron solubility. Common on pin oak, blueberry, azalea, and rhododendron planted in high-pH soils.

Correction: Soil acidification (sulfur applications) or iron chelate (chelated iron is available to plants at higher pH). For large trees with iron chlorosis, trunk injection of iron is a short-term correction; long-term soil acidification is the durable solution.

Manganese deficiency (Mn)

Symptom: Nearly identical to iron deficiency — interveinal chlorosis on new leaves — but the yellowing tends to be less dramatic (pale yellow rather than near-white) and the green veins are not as sharply contrasted. Per Penn State Extension, laboratory testing is often needed to distinguish iron from manganese deficiency conclusively.

Associated conditions: High-pH soils (like iron); alkaline organic soils; soils where iron and manganese have both been leached.

Nutrient deficiency comparison table

Recommended gear: Best evergreen and deciduous azaleas by zone — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.

Frequently asked questions

My tomatoes have yellow leaves on the bottom and green on top. Is this nitrogen or something else? Per Penn State Extension, yellowing that starts on the lower, older leaves and progresses upward on tomatoes is consistent with nitrogen deficiency (most common), magnesium deficiency (interveinal on older leaves), or the early stages of Septoria leaf spot (which also starts on lower leaves but produces spots rather than uniform yellowing). Check whether the yellowing is uniform across the leaf (N likely) or interveinal (Mg possible). Also check for tiny dark spots (Septoria).

Can I use soil test results to diagnose nutrient deficiency? Per Penn State Extension, soil testing provides the most reliable diagnosis and prevents adding nutrients that are not needed (which can cause their own problems — excess nitrogen promotes aphids and fungal disease; excess phosphorus locks up zinc and iron). University extension services offer soil testing for $10–20 and provide amendment recommendations.

Why doesn't Epsom salt fix iron chlorosis on my pin oak? Because they're different elements. Epsom salt is magnesium sulfate — it corrects magnesium deficiency. Iron chlorosis is an iron deficiency (or more accurately, iron unavailability at high pH). Per Penn State Extension, applying Epsom salt to an iron-deficient plant will have no effect on the iron chlorosis symptoms.

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Sources:

1. Penn State Extension — Nutrient deficiencies
2. Penn State Extension — Iron chlorosis
3. Penn State Extension — Blossom end rot
4. Penn State Extension — Soil testing