A mobile nutrient is an element that can be withdrawn from existing tissue and moved through the phloem to where it is needed. When supply runs short, the plant sacrifices old leaves to feed new ones, so symptoms appear on the lower canopy first. Nitrogen, phosphorus, potassium and magnesium are the classic mobile nutrients; chlorine and molybdenum are also mobile, and zinc moderately so.
In practice
Where a symptom starts is the first clue in diagnosis. Yellowing that begins at the bottom of the plant and works upward points to a mobile nutrient: even yellowing suggests nitrogen, interveinal yellowing suggests magnesium, and scorched margins suggest potassium. Some lower-leaf yellowing in late flower is normal remobilisation as the plant moves nutrients to the buds.
Don't confuse with
- Immobile nutrient: stays where it is first deposited; symptoms appear in new growth.
- Available: whether a nutrient can be taken up from the root zone is a separate question, governed mostly by pH.
The plant's living transport tissue that carries sugars, amino acids, hormones and mobile nutrients from leaves to roots, buds and other growing parts.Molybdenum (Mo) is the micronutrient needed in the smallest amount; plants need it to convert nitrate into usable nitrogen.Zinc (Zn) is a micronutrient needed for auxin production and many enzymes; deficiency gives small, twisted new leaves and shortened internodes.An immobile nutrient stays where it is first deposited, so its deficiency shows on young leaves and growing tips first: Ca, S, Fe, Mn, B, Cu.The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.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.Nitrogen (N) is the macronutrient plants use most, built into proteins, chlorophyll and nucleic acids; it drives leaf and stem growth and is fully mobile.Magnesium (Mg) is a mobile secondary nutrient at the centre of every chlorophyll molecule; deficiency causes interveinal yellowing on older leaves.Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves.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.
