Aluminium is one of the most abundant elements found on Earth. It has been found to encourage plant growth and reduce crop yield in acid soil. However, in certain forms, such as active Al ion it can be toxic to plants. Aluminium toxicity is especially present in root tip meristem. This guide will help you understand the full picture of aluminium’s effect on plants.

Most of the research on the effects of aluminium on plant growth used high levels (toxic levels) of aluminium. Comparatively, low levels of aluminium can induce plant growth. Other benefits of low levels of aluminium include:

  • An increase in phosphorus efficiency
  • Alleviating certain toxicities such as manganese, iron, and H+
  • Promotes rhizobacteria

Plant Growth in Acid Soil

Soil acidification is most prevalent in areas where agricultural production is more abundant. Improved plant growth as a result of low doses of Aluminium has been documented in many different plant species, such as:

  • Melastoma malabathricum L
  • M. malabathricum
  • Miscanthus sinensis
  • Cowpea
  • Eucalyptus gummifera
  • And much more

The mechanism by which aluminium improves plant growth can be attributed at least in part to its improvement of nitrogen, phosphorus, and potassium uptake. Aluminium also alleviates H+, iron, and manganese deficiency in acidic soil as well as activates genes that are associated with tolerance to abiotic stress. 

Another contributing factor in plant growth is aluminium’s ability to stimulate rhizobacteria, which promotes plant growth.

Aluminium & Soil Acidity

When aluminium is added to garden soil, it lowers the soil pH in fruit and cereal crops and other acid-loving plants. Aluminium is effective in lowering the soil pH in these plants when tests show the pH is at least one point higher than normal. Excessive amounts of aluminium are toxic to plants.

Aluminium Toxicity in Soil

You can check for signs of aluminium toxicity but the only sure-fire way to know is to conduct a soil test that measures pH levels and nutrient deficiencies. Watch out for the following symptoms:

  • Short plant roots – Toxic levels of aluminium negatively affect root growth because it affects root cell division. Roots can be shortened to half the length of their non-toxic soil counterparts. A byproduct of this is that the shorter roots are less apt at withstanding drought and less efficient and intaking nutrients.
  • Low pH – When the soil solution aluminium dips below a pH of 5, it reacts with root cell wall materials and cell membranes which cause restriction in cell wall expansion and root growth.
    • Between 5 and 5.5: Slightly toxic levels of aluminium
    • Below 5: Likely contains aluminium in toxic levels
    • Above 6: No toxic levels of aluminium
  • Nutrient Deficiency – Growing plants in soil containing toxic levels of aluminium display nutrient deficiency symptoms such as stunted growth, pale colour, and failure to thrive. 

Shorter roots as a result of aluminium deficiency contribute to this as well as the tendency for phosphorus and sulphur to combine with aluminium instead of being bioavailable for plant intake.


Aluminium is a powerful element, acting as both a friend and foe to plants, depending on its dosage. If there is a sufficient amount of organic matter in topsoil, it can prevent the aminium from becoming toxic to plant roots because they remain bound. 

While it has been documented as improving plant growth, nutrients, and resistance to abiotic stress in low levels, at high levels it can be toxic and cause nutrient deficiency and short roots. At Bisley International, we sell aluminium sulphate, which acidifies soil by lowering its pH. This makes the soil an ideal home for acid-loving plants. Have any questions? Contact us today!