Nutrient deficiencies are indicated with unusual leaf colours or patterns, which should be used to diagnose the cause

in heavy clay soil and areas with very high rainfall. Phosphorus deficiency can be remedied with fertilisers such as superphospate or blood and bone.

Deficiencies in minor or trace elements

Acidic, sandy and coarse soils often contain less calcium, which helps to form the cell wall structure. Bitter pit and water core disorders in apples are associated with calcium deficiency and erratic watering. Calcium can be applied using lime, superphosphate and gypsum but remember that it is quickly leached out in heavy rain.

New Zealand soils are notably short in the trace element boron, so this deficiency is more commonly seen here. Boron is required for healthy plant cell formation, and a shortfall can be seen in, for example, pears with dimples on the skin with brown patches in the flesh underneath. Boron is usually applied as a foliar spray (meaning a liquid solution of fertiliser sprayed onto the tree itself, absorbed through the leaves). Yates Health Tonic Trace Element Chelate contains a range of trace elements including boron, and can be applied as a foliar feed to all plants except stonefruit (where it can be applied as a root drench).

Magnesium is required for healthy leaves and for plants to photosynthesise properly. Deficiencies are more common on light, sandy soils and where potassium-rich fertilisers are used (as plants prefer to take up potassium over magnesium). Symptoms are a yellowing between the leaf veins, with some reddishbrown tinges. Fruit trees that are known to be sensitive to magnesium deficiency include apples, grapes and raspberries.