An immobile nutrient is an element that, once built into a leaf, cannot be readily moved through the phloem to other tissue. New growth depends entirely on current supply from the roots. Calcium, sulfur, iron, manganese, boron and copper are usually classed as immobile or poorly mobile.
In practice
When new growth is pale, distorted or dying while old leaves look fine, suspect an immobile nutrient. Interveinal yellowing on the newest leaves points to iron; distorted, spotted new leaves to calcium or boron; even pale new growth to sulfur. Calcium is a special case: it moves only with water in the xylem, so low transpiration under high humidity can starve new growth even when the feed holds plenty. Because these elements depend on root uptake, pH problems often show up here first.
Don't confuse with
- Mobile nutrient: remobilised from old leaves; symptoms start low.
- Unavailable: a nutrient can be present but locked out by pH; mobility is about movement inside the plant.
Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.Manganese (Mn) is a micronutrient that splits water in photosynthesis and activates many enzymes; low pH can raise it to toxic levels.Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow.The plant's water-conducting tissue, which carries water and dissolved mineral ions upward from roots to leaves, driven mainly by transpiration.The evaporation of water from a plant, mainly through open stomata, which pulls water and dissolved nutrients up from the roots.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.A mobile nutrient is one the plant can move from older leaves to new growth, so its deficiency shows first on lower, older leaves: N, P, K, Mg, Cl, Mo.Nutrient lockout is when plants show deficiency symptoms although nutrients are present, because pH, salt build-up, ion antagonism or damaged roots stop uptake.Calcium (Ca) is an immobile secondary nutrient that builds cell walls and membranes; it travels only in the transpiration stream, so deficiency appears in new growth.Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins.A nutrient deficiency is a shortage of an essential element in the plant tissue, causing characteristic symptoms; the cause is often pH or uptake rather than an empty feed.
