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.
Possible causes
• Insufficient or incorrect fertilization
• The cultivation is on soil that fixes calcium.
• Excessive ‘table salt’(sodium) in the root environment.
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 fertilizers can cause magnesium deficiency, as plants take up potassium in preference to magnesium.
Possible causes
• A very wet, cold and/or acidic root environment.
• High levels of potassium, ammonium and/or calcium (for example a lot of lime in the tap water or lime rich, clay ground) compared with the magnesium levels.
• Limited root system and a heavy load on the plants.
• High EC in the medium, inhibited evaporation.
Manganese and iron are important for allowing plants to harness the energy of the sun (photosynthesis). Soil shortages are rare, but manganese and iron can be unavailable to plant roots in alkaline conditions. Ericaceous (acid-loving) plants are particularly vulnerable when growing in alkaline soils or potting composts.
Possible causes
• Poorly drained soils
• Plants where pH is high
• Can be due to leaching in the acid soils and to insolubility in the alkaline soils.
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.
Possible causes
• Conditions where the pH is too high (>pH7) in the growing medium. Under these circumstance the plants can barely absorb phosphorous at all and insoluble phosphorus compounds form in the soil.
• If the growing medium is rich in iron or zinc or if it is too acidic.
• Because of soil fixation.
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.
Possible causes
• Conditions where the pH is too high (>pH7) in the growing medium. Under these circumstance the plants can barely absorb phosphorous at all and insoluble phosphorus compounds form in the soil.
• If the growing medium is rich in iron or zinc or if it is too acidic.
• Because of soil fixation.
