# Brown or burnt leaf tips on cannabis: a differential

> Crispy brown tips on otherwise healthy leaves usually mean too much salt in the root zone (EC too high, or salts building up because of low runoff or drying out), not a deficiency. Check runoff or reservoir EC against input first, then watering rhythm, then heat and low humidity, and only then K or B disorders.

- Canonical: https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.html
- Category: Diagnosis · Level: Beginner
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Seedling, 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 tips of my cannabis leaves brown and crispy?** Brown, crispy tips on otherwise dark green cannabis leaves usually mean salt burn: root-zone EC is too high, or salts are concentrating because the medium dries out or gets too little runoff. Leaf tips sit at the end of the water path, so they die first. Check runoff or [reservoir EC](https://genetixbay.com/knowledge/glossary/input-ec.md) against input first, then watering rhythm, heat and low humidity, and only then potassium or boron.

**Is brown tip burn on cannabis nutrient burn?** Brown tip burn on cannabis is most often nutrient (salt) burn, especially when 1 to 3 mm of the tip is brown on dark green, newest mature leaves. Confirm it by measuring runoff EC: runoff more than about 1.0 mS/cm above input points to [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), while runoff within about 0.5 mS/cm of input means heat, low humidity or a potassium problem is more likely.

**Why do cannabis seedlings get burnt tips?** Cannabis seedlings and fresh clones get burnt tips at feed strengths that a flowering plant would find light. Grower practice keeps seedling feed at roughly 0.4 to 0.8 mS/cm EC (200 to 400 ppm on the 500 scale). If seedling tips brown, lower the feed EC, avoid letting the medium dry hard between waterings and keep humidity up, because dry air worsens tip burn.

**How does high EC cause tip burn on cannabis?** High root-zone EC lowers the osmotic potential around cannabis roots, making water uptake harder, and salts concentrate further as the medium dries. Heat and low humidity raise [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md) and carry even more salt to the leaf tips and margins, where cells die first. Grower practice treats runoff EC more than about 1.0 mS/cm above the input EC as a sign of salt build-up.

**What is the difference between brown leaf edges and brown tips on cannabis?** Brown tips alone on dark green, newer mature cannabis leaves point to salt burn from high EC. Brown margins with a yellow band that start on the lower, older leaves point to [potassium deficiency](https://genetixbay.com/knowledge/glossary/potassium.md), which controlled trials show yellows the serrated edge before it browns. Brown edges combined with upward cupping at the top of the canopy suggest heat or [light stress](https://genetixbay.com/knowledge/glossary/light-stress.md) instead.

**How do I flush salt build-up from cannabis pots?** A [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) washes salt build-up out of the medium, not the plant, and is fine at any stage. In coco or rockwool, run 2 to 3 times the container volume of a light solution (EC about 0.4 to 0.8 mS/cm, with calcium and magnesium, pH 5.8 to 6.0) in passes until runoff EC is within about 0.5 mS/cm of input. In soil, use pH-adjusted plain water at pH 6.3 to 6.8.

**Short answer.** Brown, crispy tips on leaves that are otherwise dark green is classic salt (nutrient) burn: the root zone is too concentrated, so water is pulled out of the leaf margins first. Measure runoff or reservoir EC and compare it with what you are feeding. If EC is fine, look at watering rhythm (pots drying out concentrates salts), heat and very low humidity, and only then at potassium or boron disorders.

## What's happening

Leaf tips and margins are the end of the water path. Anything that limits water supply or concentrates salts there kills those cells first. High root-zone EC lowers the osmotic potential around roots; in drying media the salts concentrate further. Heat and low RH raise transpiration demand and deliver more salts to the tip. True K deficiency starts on *lower* leaves with yellowing of the serrated margin before browning [1]; in DWC flowering trials K deficiency caused scorching of fan-leaf tips and margins and dark lesions on [sugar leaves](https://genetixbay.com/knowledge/glossary/sugar-leaf.md) [2]. Boron *toxicity* caused marginal yellowing then browning on lower leaves [1].

## How to recognise it

| Pattern | Most likely | Also consider |
|---|---|---|
| Tips only, 1–3 mm brown, leaves dark green, newest mature leaves | Mild salt/nutrient burn (EC high) | Feed too strong for seedlings |
| Tips plus dark, glossy leaves curling down at tips ("claw") | Excess N plus high EC | See [clawing](https://genetixbay.com/knowledge/diagnosis/clawing-leaves.md) |
| Brown margins with yellow band, lower leaves first | Potassium deficiency [1] | Salt build-up, Mn/B toxicity |
| Brown edges plus upward cupping at top of canopy | Heat or light stress | Low RH, see [taco](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md) |
| Brown tips across many plants after a dry spell | Drought plus salt concentration | Irrigation failure |
| Brown spots in the leaf body, not just tips | Not tip burn: see [rust spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md) | Ca, P, leaf septoria |

## Numbers that matter

| Parameter | Target | Notes |
|---|---|---|
| Seedling feed EC | ~0.4–0.8 mS/cm (200–400 ppm500) | Grower practice |
| Veg feed EC | ~1.0–1.8 mS/cm (500–900 ppm500; 700–1260 ppm700) | Grower practice; DWC trial used 1.8 dS/m [2] |
| Flower feed EC | ~1.6–2.4 mS/cm (800–1200 ppm500) | Grower practice |
| [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) vs input | within ~0.5 mS/cm | Grower practice; > 1.0 above input = build-up |
| Runoff volume (coco/rockwool, [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md)) | 10–30% of irrigation | Grower practice |
| RH, veg | ~55–70% | Grower practice; very low RH worsens tip burn |
| Air temperature | [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) declined above ~30 °C (86 °F) in one cultivar | [5] |

## What to check first

1. **Runoff/reservoir EC** versus input EC. The single most useful reading.
2. **Feed strength vs stage.** Seedlings and fresh clones burn at EC that a flowering plant would find light.
3. **Watering rhythm.** Coco or rockwool allowed to dry hard between irrigations concentrates salts; small sips with no runoff build salts.
4. **Climate.** [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) and RH at the canopy. Hot, dry rooms produce tip burn at moderate EC.
5. **pH.** Rarely the direct cause of tip burn, but out-of-range pH changes which salts accumulate; targets are 5.5–6.0 in hydro and 5.5–6.5 in soilless media [4].
6. **Pattern by leaf age** to separate K deficiency (old leaves, yellow band first) from burn (newest mature leaves, tips first).

## How to fix it

- **Hydro:** dilute or replace the reservoir to a lower EC (drop 0.2–0.4 mS/cm). Top up evaporation losses with plain pH-adjusted water, not full-strength feed.
- **Coco/rockwool:** do a **root-zone flush**: run about 2–3× the container volume of a light solution (EC ~0.4–0.8 mS/cm, with Ca and Mg, pH ~5.8–6.0) through in several passes until runoff EC is within ~0.5 mS/cm of the flush input. Then go back to normal feed with consistent runoff. Plain water strips Ca and Mg from coco.
- **Soil:** root-zone flush with 2–3× the pot volume of pH-adjusted plain water (pH ~6.3–6.8), slowly and in passes, then check runoff EC and resume normal feeding once the top few cm dry. Do not drown a pot that is already wet.

This root-zone flush treats the medium, not the plant, and is fine at any stage (see [the root-zone flush](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). It is not a pre-harvest flush, which is a *Myth* that costs yield and resin.
- **Climate:** raise RH towards the stage target, lower leaf temperature, reduce light intensity if leaves are hot.
- **True K deficiency (confirmed by pattern and normal EC):** increase K in the feed modestly. Bevan et al. found flowering yield in soilless cannabis was relatively insensitive across moderate K rates, so big K additions are rarely justified [3].

## How to confirm it worked

- New leaves develop without brown tips (5–10 days).
- Runoff EC trends toward input EC over 2–3 irrigations.
- Existing burnt tips stay burnt; they do not spread inward if fixed.

## Common mistakes

- Reading the brown tip as hunger and feeding harder.
- Topping up a hydro reservoir with full-strength nutrient; EC creeps up as water evaporates.
- Ignoring runoff in coco. No runoff = salts with nowhere to go.
- Cutting off every crispy tip; harmless, but pointless.

## Evidence

- [Salt stress](https://genetixbay.com/knowledge/glossary/sodium.md) causing marginal and tip necrosis is *Established* horticultural physiology. Specific cannabis EC limits are *Grower practice*.
- K deficiency and B toxicity patterns in cannabis are *Established* in controlled trials [1][2].
- Heat effects on cannabis photosynthesis are *Supported* [5].

## 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. Bevan L, Jones M, Zheng Y., 2021. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103
4. Velechovský J, et al., 2024. Frontiers in Plant Science 15:1322824. https://doi.org/10.3389/fpls.2024.1322824
5. Chandra S, Lata H, Khan IA, ElSohly MA., 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x