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Nutrient deficiencies

If plants fail to thrive, despite adequate soil preparation, watering and mulching, it may be a sign of a nutrient deficiency. Fruit and vegetables are particularly vulnerable, as are containerised plants and those growing in very acid or alkaline soils. Yellow or reddish coloured leaves, stunted growth and poor flowering are all common symptoms of nitrogen, magnesium or potassium deficiency.

Quick facts Plants affected All plants 

Main causes Very acid or alkaline, or thin sandy soils; poor growing conditions
Timing Usually spring or summer

What are nutrient deficiencies?

Some garden soils and potting composts suffer from a lack of nutrient content, leading to deficiency symptoms in the plants growing in them.

Plants can also suffer deficiencies where the growing conditions are poor and the plants are unable to take up nutrients present in the soil. Very acid or alkaline conditions, dryness and waterlogging can all make it difficult for plants to take up soil nutrients.

Nutrient deficiencies cause symptoms such as leaf yellowing or browning, sometimes in distinctive patterns. This may be accompanied by stunted growth and poor flowering or fruiting.

Symptoms, cause and remedy

Nitrogen deficiency

Symptoms: Spindly yellow plants or yellow leaves, sometimes with pink tints.
Cause: Nitrogen promotes green, leafy growth and deficiency results in yellowing and stunted growth. Nitrogen is very soluble, so is easily washed out of the soil in winter rains, leaving the soil deficient in spring, just when plants are putting on new growth. Nitrogen deficiency is a common cause of yellow leaves in spring.
Remedy: In the long term, mulching with organic matter (such as well rotted garden compost or manure) provides a steady trickle of nitrogen to stabilise levels. In the short term, applying high nitrogen fertilisers such as sulphate of ammonia or poultry manure pellets will remedy the problem.

Potassium deficiency

Symptoms: Yellow or purple leaf-tints with browning at the leaf edge and poor flowering or fruiting.
Cause: Potassium is needed for controlling both water uptake and the process allowing plants to harness energy from the sun (photosynthesis). Potassium promotes flowering, fruiting and general hardiness. Shortages are more likely on light, sandy or chalky soils where potassium is easily washed away. Clay soils, by contrast, hold potassium within their structure.
Remedy: Apply high potassium fertilisers such as sulphate of potash, tomato feed or certain organic potassium sources derived from sugar beet processing.

Phosphorus deficiency

Symptoms: Slow growth and dull yellow foliage.
Cause: Phosphorus is needed for healthy roots and shoot growth. Soil shortages of phosphorus are rare, but may occur in areas with high rainfall and heavy clay soil.
Remedy: Apply fertilisers such as superphosphate or bone meal.

Magnesium deficiency

Symptoms: Yellowing between the leaf veins, sometimes with reddish brown tints and early leaf fall. Magnesium deficiency is common in tomatoes, apples, grape vines, raspberries, roses and rhododendrons.
Cause: Magnesium is needed for healthy leaves and for plants to harness energy from the sun (photosynthesis). Soil shortages of magnesium are more common on light, sandy soils. Over-use of high-potassium fertilisers (such as tomato feed) can cause magnesium deficiency, as plants take up potassium in preference to magnesium.