# Yellow new growth on cannabis: a differential

> Yellowing at the top of the plant points to an immobile nutrient (Fe, S, Mn, Zn, Cu, B, Ca) that the roots are failing to deliver, and the usual cause is high root-zone pH or a wet, cold or damaged root zone rather than a lack of fertiliser. Rule out light bleaching, broad/russet mites and viroid stunting before adding micronutrients.

- Canonical: https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.html
- Category: Diagnosis · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Flower · 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

**Why are the new leaves on my cannabis yellow?** Yellow new leaves on cannabis mean the plant is short of an [immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), such as iron, sulfur, manganese, zinc, copper, boron or calcium, that it cannot move from old leaves. In most grows the feed contains these, so the real cause is failed uptake: root-zone pH too high or roots that are wet, cold or damaged. Rule out [light bleaching](https://genetixbay.com/knowledge/glossary/light-stress.md) and mites first.

**Why is the top of my cannabis plant yellow but the bottom green?** A cannabis plant yellow at the top and green at the bottom has an uptake problem with immobile nutrients. Controlled trials show [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md) yellows new leaves between the veins while lower foliage stays dark green. First check whether only the tops nearest the light are pale (bleaching), then root-zone pH, which should stay within 5.5 to 6.5 in coco or rockwool.

**Is yellow new growth on cannabis iron deficiency?** Yellow new growth on cannabis is iron deficiency when the yellowing is interveinal with sharply green veins at the top only, but in coco and hydro it is usually pH-induced rather than a true shortage. Iron and manganese availability falls above about pH 6.5. Correct root-zone pH first; adding iron to a pH 7 pot precipitates and does nothing.

**Why are the tops of my cannabis bleached white under an LED?** Bleached white tops directly under an LED, with the lower canopy fine, are light and heat bleaching, not a nutrient problem. It starts as pale, then white, leaves and bracts at the very top. Raise the fixture 10 to 15 cm or dim it, keep [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) below about 30 °C (86 °F), and measure PPFD. Bleached tissue will not recover.

**What causes twisted yellow new growth on cannabis?** Twisted, shiny, glassy or bronzed yellow new growth on cannabis is most often broad or [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md), which are nearly invisible without a 20x or stronger lens, according to extension sources. Calcium or boron deficiency can also distort new leaflets and kill tips. Inspect the [growing tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) with a lens before spraying micronutrients, because mites move fast and keep feeding.

**Short answer.** If the top is yellow and the bottom is green, the plant is short of something it cannot move from old leaves: iron, sulfur, manganese, zinc, copper, boron or calcium. In most grow rooms the fertiliser contains all of these; what has failed is uptake, usually because root-zone pH is too high or the roots are wet, cold or damaged. Before you buy micronutrients, rule out light bleaching (tops nearest the light), broad or russet mites (twisted, shiny, glassy new growth) and viroid infection (stunted, pale, brittle plants).

## What's happening

Immobile elements must arrive fresh through the roots to every new leaf. Any interruption shows first at the growing tips. In cannabis trials, Fe deficiency produced interveinal chlorosis on new and expanding leaves while lower foliage stayed dark green [1]; Mn deficiency produced bright yellow netted interveinal chlorosis on upper and central foliage in sand culture [1] but no visible symptoms in DWC [2]; Zn deficiency produced marginal yellowing of new leaves turning to tan necrosis [1]; S deficiency gave general paling with the base of leaflets most yellow, intensifying on new leaves [1], and in DWC flowering plants it yellowed upper [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) first [2]; Ca and B deficiency distorted new growth, narrow leaflet bases and dying tips [1].

Iron and manganese availability falls as pH rises above ~6.5 in soilless media [3], which is why "iron deficiency" in coco or hydro is so often a pH problem.

## How to recognise it

| Pattern on new growth | Most likely | Also consider |
|---|---|---|
| Interveinal yellow, veins sharply green, top only | Iron (often pH-induced) | Mn; cold, wet roots |
| Netted yellow between veins, small tan specks | Manganese | Fe; pH high |
| Pale overall, leaflet base yellowest, top half | Sulfur | N if spreading from bottom too |
| Yellow margins on new leaves, then tan edges | Zinc | Heat/light stress |
| Distorted, narrow, crinkled leaflets; dying tips | Calcium or boron | Broad/russet mites, herbicide drift, HLVd |
| White/bleached tops directly under light, lower canopy fine | Light/heat bleaching | Not a nutrient at all |
| Twisted, shiny, glassy, bronzed new growth; leaves cupping | Broad or russet mites [5] | Ca/B deficiency |
| Whole plant stunted, small pale leaves, [short internodes](https://genetixbay.com/knowledge/glossary/node-stacking.md), brittle stems | Hop latent viroid [6] | Root rot, root aphids |

## Numbers that matter

| Parameter | Target | Notes |
|---|---|---|
| pH, hydro | 5.5–6.0 | [3] |
| pH, coco/rockwool | 5.5–6.5 | Above 6.5, Fe and Mn availability falls [3] |
| Leaf Fe, healthy | ~100–150 mg/kg | Survey range in [1]; deficient plants 60 mg/kg |
| Leaf Mn, healthy | ~41–93 mg/kg | [1] |
| Leaf Zn, healthy | ~24–52 mg/kg | [1] |
| Leaf S, healthy | ~0.17–0.41% | Survey 0.17–0.26%; controls 0.41% [1] |
| Canopy PPFD | flower ~900–1500 µmol/m²/s | Yield rose linearly to 1800 in one trial [4], but bleaching occurs on some cultivars at high PPFD |
| Canopy leaf temperature | < ~30 °C (86 °F) | Grower practice |

## What to check first

1. **Light.** Are the yellow/white tops only the ones closest to the fixture? Measure PPFD or raise the light 10–15 cm. Bleaching starts as pale, then white, leaves and bracts at the very top.
2. **pH at the root zone.** Runoff or reservoir, calibrated meter. A pH of 6.8 in coco is a likely Fe/Mn lockout.
3. **Root zone.** Cold (< 18 °C / 64 °F), waterlogged, or rotting roots. New growth suffers first when roots are compromised.
4. **Hand lens on new growth.** 20× or better. Broad mites are nearly invisible to the eye [5]; look for shine, bronzing and twisted tips.
5. **Whole-plant pattern.** One plant stunted and pale in a room of healthy ones (same feed) suggests a pathogen or viroid; test if it is a mother or a clone source.
6. **Feed check.** Is it a complete fertiliser with micronutrients? [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) with an incomplete base nutrient can genuinely lack S or micros.

## How to fix it

- **Light:** raise or dim to reduce top-of-canopy PPFD and leaf temperature. Bleached tissue will not recover.
- **pH:** bring the root zone back into range. In coco, irrigate to 20–30% runoff with correctly pH'd solution; in hydro, change the reservoir. Fe and Mn uptake typically recovers in days.
- **Root zone:** warm it, aerate it, water less often. See [drooping](https://genetixbay.com/knowledge/diagnosis/drooping-overwatering-vs-underwatering.md) and [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md).
- **True micronutrient shortage (rare with complete feeds):** use a chelated micronutrient product at label rate. A [chelated iron](https://genetixbay.com/knowledge/glossary/iron-chelate.md) [foliar spray](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) can green new growth in veg within days; do not spray flowers.
- **Sulfur:** most complete feeds supply it via sulfate salts (e.g. [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md)). Check your base nutrient label.
- **Mites:** see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md). Do not delay; they move fast.
- **Suspected viroid:** isolate, test (RT-PCR on roots and leaves), and remove positives from propagation. See [HLVd](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md).

## How to confirm it worked

- The next pair of leaves at each tip emerges green, within 5–10 days.
- The yellowing does not spread to further new growth.
- With mites, new growth stops twisting within 1–2 weeks of control.

## Common mistakes

- Adding iron to a pH 7 coco pot. It precipitates and the plant still can't use it.
- Mistaking light bleaching for nitrogen or iron shortage.
- Spraying micronutrients on a plant with broad mites while the mites keep feeding.
- Overdosing boron or zinc "just in case"; boron toxicity in cannabis caused marginal yellowing and necrosis of lower leaves [1].

## Evidence

- Upper-leaf symptoms of Fe, Mn, S, Zn, Ca and B deficiency in cannabis are *Established* in sand culture [1], with partial confirmation in DWC [2]. The Mn result differs between studies: *Contested* how often Mn deficiency is visible.
- pH-induced Fe/Mn unavailability is *Established* in horticulture and *Supported* for cannabis [3].
- Light bleaching thresholds are *Grower practice*; yield responses to high PPFD are *Supported* [4].
- Broad mite and HLVd symptoms are *Supported* by extension sources [5][6].

## Sources

1. Cockson P, et al., 2019. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432
2. Llewellyn D, Golem S, Jones AMP, Zheng Y., 2023. Plants 12(3):422. https://doi.org/10.3390/plants12030422
3. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824
4. Rodriguez-Morrison V, Llewellyn D, Zheng Y., 2021. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020
5. UConn IPM. Managing Broad Mites on Greenhouse Crops. https://ipm.cahnr.uconn.edu/ipm-managing-broad-mites-on-greenhouse-crops
6. Pacific Northwest Plant Disease Management Handbook. Hemp (Cannabis sativa)-Viroid Diseases. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-viroid-diseases