Work out which leaves are affected first before you reach for any fertiliser: that one detail does more diagnostic work than the colour or pattern of the damage. If older, lower leaves go pale or yellow while the newest growth looks fine, the cause is a nutrient the plant can move around internally (nitrogen, phosphorus, potassium, magnesium). If the newest leaves are hit while the old ones stay green, suspect a nutrient the plant can't relocate (iron, boron, zinc, calcium), or an environmental stress such as wind, frost or waterlogging.
Quick answer
Nutrients a plant can relocate (nitrogen, phosphorus, potassium, magnesium) show a shortage on the older leaves first, because the plant strips them from old growth to protect new growth. Nutrients it can't relocate (iron, boron, zinc, calcium) show in whatever is growing now, so the newest leaves are hit first. Match the pattern below, then check old against new before treating anything.
The tables cover ten nutrient deficiencies that most often show as leaf symptoms in the garden, and five non-nutrient stresses that get mistaken for them, followed by detail on the pairs that are easiest to confuse.
Before you diagnose
Growing conditions, including drought, waterlogging, light deprivation or poor establishment, can resemble deficiencies. If a plant fails to thrive despite good soil preparation, watering and mulchingA layer of material spread over the soil around plants to suppress weeds, retain moisture, and improve soil structure as it breaks down. Full definition →, a nutrient deficiency becomes the more likely explanation. A cheap home soil pH test kit is worth using before treating anything, since extreme pH, acid or alkaline, reduces nutrient availability whatever the soil holds, and iron and boron problems in particular are often a pH lockout rather than a true absence of the nutrient. That matters in Scotland, where a meaningful share of soil is on the acid side (see "The Scotland soil question" below).
A feed doesn't repair leaf tissue that has already yellowed, browned or distorted; it only corrects what grows next. Don't judge a fix by watching damaged leaves recover, since they won't. Watch the newest growth over the following weeks instead.
Nutrient deficiency table
| Symptom | Which leaves first | Nutrient | What to do |
|---|---|---|---|
| Pale yellow, spindly, stunted growth, sometimes with pink tints | Older leaves, spreading to younger foliage as it worsens | Nitrogen (N) | General-purpose liquid feed or a nitrogen-rich fertiliser such as poultry manure pellets; mulch with organic matter for the longer term |
| Stunted growth with purple discolouration, eventually turning dull yellow | Older leaves (most visible in seedlings, rarely seen once plants are mature) | Phosphorus (P) | General-purpose liquid fertiliser in containers; improve drainage in open ground and hold off planting tender crops until soil has warmed |
| Yellow or purple-red tints with browning starting at the leaf edges | Mature/older leaves | Potassium (K) | Potassium-rich feed such as comfrey pellets or a seaweed-based fertiliser |
| Yellowing between the leaf veins, sometimes reddish-brown; leaves eventually brown, develop dead patches and drop early | Older leaves | Magnesium (Mg) | Magnesium sulphate (Epsom salts) at about 30g per square metre long term, or a foliar spray of 20g Epsom salts per litre, applied 2-3 times a fortnight apart on dull days |
| Rarely a distinct leaf symptom; shows far more reliably as a fruit or root-vegetable quality problem | New growth, since calcium can't be relocated from older tissue | Calcium (Ca) | Keep soil evenly moist, avoid overfeeding potassium, improve ventilation under glass |
| Thinly documented as a garden symptom; where described, general pale yellowing similar to nitrogen deficiency | Not well established | Sulfur (S) | Improve soil organic matter and overall fertility rather than chasing a specific sulfur product |
| Yellowing between leaf veins, sometimes with dead spots between veins or at leaf tips | Newest/youngest leaves | Iron (Fe) | Ericaceous compost and rainwater (not tap) for lime-hating plants in containers; chelated iron feed |
| Stunted growth with browning; tip dieback on lettuce, brown cracks in celery stalks | Newer growth | Boron (B) | Test soil pH and avoid liming alkaline soils; treat with fritted trace elements containing boron before planting |
| Yellow or purplish leaves; new growth stunted, delayed, small or narrow | New growth | Zinc (Zn) | A chelated micronutrient feed formulated for zinc |
| Yellowing between leaf veins, sometimes with leaf edge browning | Older/more mature leaves | Manganese (Mn) | Chelated manganese feed; ericaceous compost for lime-hating plants in containers |
One more nutrient is worth knowing if you grow brassicasThe cabbage family: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, swede, turnip and more, sharing the same pests, diseases and rotation rules. Full definition →: molybdenum. It locks out in acid soil, and the result has its own name, whiptail: narrow, elongated, twisted young leaves. If the soil pH is below about 6.3, liming to raise it is the fix, or fritted trace elements containing molybdenum before sowing, rather than a search for a molybdenum-specific product.
Magnesium against iron: the mechanism matters more than the colour
Magnesium can be relocated inside the plant, so when it is short the plant pulls it from older leaves to protect new growth, and the damage shows as older leaves browning with dead patches and dropping early. Iron can't be relocated once it is built into leaf tissue, so a shortage shows only in what is growing now: the youngest leaves come in yellow while the oldest stay green. Both produce the same headline symptom, interveinal yellowing with the veins staying green, which is why they get confused. Feeding Epsom salts to a plant with an iron problem, or the reverse, won't help.
Iron shortage is often a lime-induced lockout rather than a true absence of iron. It shows on lime-hating (ericaceous) plants such as rhododendrons and camellias grown in alkaline soil or watered from the tap, where iron is present but unavailable. Acid-loving plants need ericaceous compost and acid soils to take up iron and manganese, so the same plants struggle the moment they are limed, potted in ordinary compost or watered from a hard-water tap. Manganese deficiency looks almost identical in colour and pattern but shows on older leaves rather than the newest, so the two sit on opposite sides of the old and new divide.
Other pairs worth flagging
Nitrogen and potassium deficiency both start on older leaves and both cause yellowing, but potassium adds browning that starts at the leaf margins, while nitrogen's yellowing is more general across the leaf and comes with spindly, stunted growth. Phosphorus deficiency's purple discolouration is the most distinctive symptom in the group, but it is mostly seen in young seedlings and young plants such as tomatoes in cool conditions, so a purple-tinged mature plant is more likely something else. Sulfur deficiency's resemblance to nitrogen deficiency is not well established, so treat a plant that looks nitrogen-deficient as a nitrogen problem first.
Calcium's most familiar form is a fruit problem, not a leaf one. The table covers distorted new growth and tip dieback, a different mechanism from blossom end rot, where calcium is usually present in the soil but fails to reach the fruit because of an inconsistent water supply.
The Scotland soil question
Scotland's soils are on the whole more acidic and more leached than most of the rest of the UK. A large share of the country sits on podzols (23.7% of the land), which form where a cool, wet climate washes minerals and nutrients out of the topsoil and over acid rock, leaving the surface layer acidic and nutrient-poor. Acidic, leached, free-drainingSoil that lets water pass through quickly rather than pooling, so roots aren't sitting in wet ground after rain. Full definition → soil is the profile associated with magnesium and boron leaching risk in general soil-science terms, a reasonable starting expectation for parts of Scotland.
| Finding | Figure | What it means |
|---|---|---|
| Soil acidity on Scottish farmland | Almost half of 273 samples had a pH below 5.8, against a recommended 6.0-6.2 for mineral soils | The acidity itself is real and widespread, not a one-off |
| Magnesium status on the same soil | 99% of samples at moderate status or greater | Acidity isn't translating into widespread magnesium shortage on Scottish farmland |
| Phosphorus status on the same soil | One-third of samples low or very low | Phosphorus shortage is more likely than magnesium on Scottish farmland, though it shows rarely on mature plants |
| Boron status on Scottish soil | No Scottish survey figures | Worth watching on light, acidic ground, but not a confirmed Scottish finding either way |
The figures come from a survey of 273 soil samples from 20 Scottish farms (2016 to 2018), so they describe farmland rather than gardens. Containers and raised beds change the picture regardless of native soil. Compost in a pot drains and is watered far more often than open ground, so nutrients leach out faster, which is why a liquid feed suits containers better than a granular one (see fertiliser types). A gardener on naturally rich ground growing everything in raised beds or pots faces more of the leaching risk than the soil type alone suggests.
Environmental leaf stress table
These five aren't nutrient problems, but they produce leaf damage that gets mistaken for one, especially yellowing, browning and stunted growth. They describe established outdoor plants; a seedling or young transplant showing similar symptoms soon after planting out is more likely suffering transplant shock (see hardening off seedlings).
| Symptom | Cause | Fix |
|---|---|---|
| Yellowing/decay between veins, soft brown patches, dark areas along the midrib; roots blue-black, may smell sour; wilting despite wet soil | Overwatering / waterlogging | Improve drainage, let soil dry between waterings, remove badly damaged growth |
| Scorched or crisp brown patches, worst after foliar feedingA liquid fertiliser applied directly onto a plant's leaves rather than the soil, absorbed faster than a root feed. Full definition → in strong sun | Nutrient burn (over-fertilising, or feeding in bright sun) | Apply fertiliser at the labelled rate, water it in, avoid foliar feeding in direct sun |
| Brown, desiccated leaf edges, worst on the windward or most exposed side | Wind scorch | Temporary windbreak, mulch to reduce moisture loss, fleeceA lightweight, breathable fabric laid or draped over plants to trap a little warmth and keep off frost, wind and some flying pests. Full definition → small or tender plants |
| Leaves losing water faster than it's replaced; brown patches after a hot spell | Light/sun scorch | Choose plants suited to the site's light levels; keep up watering, feeding and mulching |
| Pale brown scorched patches between veins on tender young growth; blackened, water-soaked leaves on tender perennials | Frost damage | Wait until frost risk has passed before pruning out damaged growth |
Wind scorch deserves more weight on an exposed coastal or upland Scottish plot. Coastal gales carry salt as well as speed, which adds its own drying effect, and a windbreak that filters 50 to 60% of the wind, or fleece over small plants in winter, earns its keep faster there than in a sheltered urban garden.
Telling these apart from deficiencies
Wind scorch and light scorch both give brown, crisped leaf margins that can look like potassium deficiency. The giveaway is pattern: scorch is worst on the exposed or sun-facing side and appears suddenly after a spell of specific weather, while a nutrient deficiency develops more gradually and evenly regardless of which way the plant faces. Overwatering's interveinal yellowing can resemble magnesium or iron deficiency, but waterlogging comes with wet, smelly, discoloured roots and visibly saturated soil, so check the roots and soil before reaching for Epsom salts. Once you have identified a real nutrient shortage, see fertiliser types for what each feed contains and which one addresses which shortage.
Common questions
My tomato's older leaves are yellowing between the veins with a slightly reddish tint. Is that magnesium?
That pattern (interveinal yellowing with reddish-brown tints, on older leaves) matches magnesium deficiency. Epsom salts, either watered in or used as a foliar spray, is the standard fix.
Why are my newest leaves yellow while the old leaves look fine?
That points away from magnesium and toward iron, boron or zinc, which show in new growth because the plant can’t relocate them from older tissue. Iron deficiency is common on lime-hating plants such as rhododendrons growing in soil, or watered with water, that is too alkaline for them.
Is blossom end rot on my tomatoes the same as calcium deficiency in the soil?
Not usually. It is typically caused by an inconsistent water supply interrupting how calcium reaches the fruit, rather than a shortage of calcium in the soil.
Could Scotland's soil be why my plants seem short of magnesium or boron?
Scotland's soils are more acidic and more leached than much of the rest of the UK, so it is the right general direction to suspect. A Scottish farm soil survey found magnesium levels generally adequate despite the acidity, and there are no Scottish figures for boron, so treat it as a plausible risk on light, free-draining acidic ground, or in a pot or raised bed, rather than a confirmed local problem.
My plant's leaves are yellow and the soil is constantly wet. Is that a nitrogen deficiency?
Check the roots first. Waterlogged roots turning blue-black or smelling sour point to overwatering rather than a nutrient shortage, and feeding a waterlogged plant more won’t fix it. Improving drainage will.
Sources
Show the 9 sources
- RHS: Nutrient deficiencies: Nitrogen, phosphorus, potassium, magnesium, calcium, iron, manganese and boron symptoms and remedies, molybdenum/whiptail, and the general deficiency-vs-growing-conditions caveat. No dedicated sulfur section; doesn't cover zinc
- RHS: Wind scorch: Cause, symptoms and remedy for wind scorch
- RHS: Weather damage: Sun/light scorch and general wind-damage symptoms
- RHS: Frost damage: Frost symptom descriptions and recovery advice
- RHS: Waterlogging and flooding: Overwatering/waterlogging leaf and root symptoms and remedy
- RHS: Fertilisers (garden jobs): General caution on overuse causing plant damage
- UC IPM: Nutrient Deficiencies (Vegetables): Nitrogen, phosphorus, potassium and iron leaf-onset patterns, and zinc symptoms (plant physiology only, not UK or Scotland specific)
- SRUC: Acidic soils could be affecting production on many Scottish farms: 273 samples from 20 farms 2016-2018: almost half below pH 5.8, recommended 6.0-6.2, 99% moderate magnesium or better, one-third low phosphorus
- gov.scot: The Scottish Soil Framework, Chapter 3: Podzol coverage, leaching, and acidity across Scottish soils generally