Nutrient deficiencies show up in the leaves, and where the symptoms appear is the best clue. Yellowing or purpling on older, lower leaves points to a mobile nutrient such as nitrogen, phosphorus, potassium or magnesium. Symptoms on younger, upper leaves point to an immobile nutrient such as calcium, sulfur or iron. Confirm with a soil test before adding fertiliser, because many other problems look the same.
How do you read deficiency symptoms?
UConn Extension gives this rule of thumb: mobile nutrients move out of old leaves to feed new growth, so old leaves show the problem first. Immobile nutrients stay put, so new leaves show it first.
| Nutrient | Where it shows | Typical symptoms |
|---|---|---|
| Nitrogen (N) | Older leaves | Yellowing of lower leaves, slow and stunted growth, early maturity and lower yield; yellowing starts at the tip and runs along the midrib |
| Phosphorus (P) | Older leaves | Purpling of leaves and margins, stunted growth, delayed maturity |
| Potassium (K) | Older leaves | Yellowing and browning along leaf edges; upper new leaves may stay green |
| Calcium (Ca) | Younger leaves | Poor leaf expansion, curling, dead patches, misshapen fruit; blossom end rot in tomato and pepper |
| Sulfur (S) | Younger leaves | Stunted plants, thin stems; in cabbage-family crops pale young leaves, reddish undersides, cupped leaves; likelier in sandy, low-organic soils |
How do you confirm it is a deficiency?
UConn Extension says the best way to confirm a deficiency is to test your soil and plant tissue. It also warns that disease, drought, excess water, herbicide or pesticide injury, insects, salt injury and genetic problems can mimic deficiencies, and several deficiencies can occur together. Use our soil test interpreter to make sense of a lab report.
Should you add calcium when you see blossom end rot?
Not by reflex. The same guide says to check soil moisture first, since drought can limit how calcium moves through the plant. Read our blossom end rot guide for the full fix.
What should you do next?
- Check watering and drainage before blaming nutrients. See why plant leaves turn yellow.
- Get a soil test and compare it with what your crop needs.
- If nitrogen is low, see how to add nitrogen to soil.
- Work out feeding amounts with the garden fertilizer calculator.
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Frequently asked questions
Which leaves show nitrogen deficiency first?
The older, lower leaves, which turn yellow while growth slows.
Why are my leaves purple?
Purpling of leaves and margins is a classic sign of low phosphorus, but other stresses can look similar, so test first.
Can too much fertiliser cause leaf damage?
Salt injury is one of the stresses that can mimic a deficiency, according to UConn Extension.
Reviewed November 2026. Sources: UConn Home & Garden Education Center: Nutrient deficiency symptoms
