# Mobile vs immobile nutrients: reading old vs new leaves

> Mobile nutrients (N, P, K, Mg, and also Cl, Mo, Ni) can be moved from old leaves to new ones through the phloem, so their shortages show on the oldest, lowest leaves first. Immobile nutrients (Ca, B, Fe, Mn, Cu, Zn, and partly S) stay where they were first deposited, so shortages show on new growth. It is the first fork in any deficiency diagnosis, with a few cannabis-specific exceptions.

- Canonical: https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.html
- Category: Nutrients · Level: Beginner
- Evidence: Established · Status: Draft: awaiting expert review
- Stage: Any stage · Systems: Any system
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Which nutrients are mobile in cannabis?** The mobile nutrients in cannabis are nitrogen, phosphorus, potassium and magnesium, plus chloride, nickel and, moderately, molybdenum. The plant can reload them into the phloem and move them from old leaves to new growth, so their shortages show first on the oldest, lowest leaves. Calcium, boron, iron, manganese, copper and zinc are immobile or low-mobility, and sulfur is intermediate.

**Why do deficiencies show on bottom leaves or top leaves?** Cannabis deficiencies show on bottom or top leaves depending on nutrient mobility. Mobile nutrients such as nitrogen, phosphorus, potassium and magnesium are stripped from old leaves to feed new growth, so lower leaves suffer first. Immobile nutrients such as calcium, boron and iron stay where first deposited, so new growth depends on daily root supply and shows shortages first.

**Yellow new growth vs yellow old leaves, what does it mean?** Yellow old leaves on cannabis point toward a shortage of a mobile nutrient: nitrogen, magnesium, potassium or phosphorus. Yellow new growth points toward an immobile nutrient: iron, manganese, zinc, calcium, boron, copper or sulfur. Before adding anything, rule out root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) and root health, because most new-growth symptoms in a properly fed plant are pH or root failures.

**Is calcium mobile or immobile?** Calcium is immobile in cannabis: it barely enters the phloem, so the plant cannot move it from old leaves to new ones, and symptoms usually start at [growing tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) and new leaves. There is a cannabis-specific exception, though. In a [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) flowering trial, withholding calcium produced spotting on lower [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) first, so spots on old leaves do not rule calcium out.

**How do I tell nitrogen from iron deficiency?** Nitrogen deficiency in cannabis starts on the oldest, lowest leaves and yellows the whole leaf, climbing up the plant, because nitrogen is mobile. Iron deficiency starts on the newest, expanding leaves and yellows between green veins, because iron is immobile. Check root-zone pH before treating iron, and remember old-leaf fading near harvest is normal remobilisation.

**Short answer.** Some nutrients can be pulled out of old leaves and sent to new growth through the phloem; others stay where they were first laid down [1]. Shortages of **mobile** nutrients (N, P, K, Mg) show first on the oldest, lowest leaves. Shortages of **immobile** nutrients (Ca, B, Fe, Mn, Cu, Zn, and partly S) show first on new growth [1][4]. Where the symptom starts is the first fork in diagnosis. Cannabis has a few exceptions, below.

## What's happening

Water and dissolved nutrients rise from the roots in the **xylem**, pulled by [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md). Everything reaches leaves that way first. What differs is whether the plant can reload a nutrient into the **phloem** (the sugar-transport system) and send it to growing tips [1].

- **Mobile:** N, P, K, Mg, Cl, Mo (moderate), Ni [1][5]. When supply falls, the plant strips them from old leaves. Old leaves yellow; new leaves look normal for a while.
- **Immobile:** Ca and B (barely enter phloem in most species), Fe, Mn, Cu, Zn (low mobility) [1][4]. New growth depends on what the roots deliver *today*. New leaves suffer; old leaves stay green.
- **Intermediate:** S. Mobility depends on N status; symptoms tend to appear mid-canopy and on newer leaves [1][2].

## How it shows in cannabis

| Nutrient | Mobility | Where symptoms started in cannabis trials |
|---|---|---|
| N | Mobile | Lower leaves, climbing up [2][3] |
| P | Mobile | Lower, older leaves (olive or brown spots) [2][3] |
| K | Mobile | Margins of lower leaves [2]; [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) in DWC flower [3] |
| Mg | Mobile | Lower leaves, interveinal [2][3] |
| S | Intermediate | Middle of plant, then new leaves [2]; upper sugar leaves [3] |
| Ca | Immobile | Growing tips and new leaves [2]; **but lower fan leaves in DWC flower** [3] |
| Fe | Immobile | New, expanding leaves [2] |
| Mn | Low | Upper and central leaves [2] |
| Zn | Low | Newer leaves, margins [2] |
| Cu | Low | New leaves, distortion and limpness [2] |
| B | Immobile | Growing tips, new leaves, root tips [2] |
| Mo | Moderate | No visible symptoms in 9 weeks [2] |

## Decision steps

1. **Where did it start?** Oldest leaves → think N, Mg, K, P. New leaves → think Fe, Mn, Zn, Ca, B, Cu, S.
2. **What pattern?** Whole leaf (N, S), between veins (Mg old, Fe/Mn new), margins (K old, Zn new), spots (P, Ca), distortion (Ca, B, Cu).
3. **Then rule out the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) and pH** before any nutrient: most immobile-nutrient symptoms in a properly fed plant are pH or root failures [4]. See [how to diagnose any problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md).

## Common mistakes

- Treating mobility as absolute. The Ca result in DWC [3] shows spotting on lower leaves can still be Ca.
- Forgetting that pests ([broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md), [thrips](https://genetixbay.com/knowledge/glossary/thrips.md)) and [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) also hit new growth first.
- Diagnosing late flower: plants remobilise N, P, K and Mg into flowers by design, so old-leaf fading near harvest is normal.

## Evidence

- Phloem mobility classes: *Established* [1].
- Cannabis symptom locations matching the classic pattern: *Established* for most elements [2][3], with the Ca exception noted [3].

## Sources

1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9
2. Cockson P, et al. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432
3. Llewellyn D, et al. 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422
4. Lopez RG, Mickelbart MV, Pasian C. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf
5. White PJ, Broadley MR. 2001. Annals of Botany 88(6):967-988. https://doi.org/10.1006/anbo.2001.1540