# Short, stubby, brown root tips: likely causes and fixes

> Short, stubby, brown root tips on cannabis is most often Nutrient burn (feed too strong), Salt build-up in the root zone or Copper toxicity (copper sprays, ionisers, pipework). How to tell them apart, the fix for each and what recovery looks like.

Also called: roots burnt, short roots, root tips brown and dead, stunted roots.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=stubby-root-tips

## Likely causes, most likely first

### Nutrient burn (feed too strong) (Possible)

- Kind: Too much of something; urgency: Low urgency
- Fix: Drop input EC by 0.3-0.5 mS/cm (or to about two-thirds strength); seedlings and clones need 0.4-1.0 mS/cm. Soil with pre-loaded nutrients usually needs plain pH-adjusted water for the first 2-4 weeks. If runoff is far above input, do a root-zone flush (see salt build-up).
- Recovery: No new tip burn on leaves that open after the change, within 5-7 days; burnt tips stay.
- Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.
- Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable.
- Article: [Brown or burnt leaf tips on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/brown-burnt-tips.md)

### Salt build-up in the root zone (Less likely)

- Kind: Root zone; urgency: Deal with it this week
- Fix: Root-zone flush: water slowly with pH-adjusted, quarter- to half-strength feed (not plain water in coco) to 20-30% runoff, about 2-3x the pot volume, until runoff EC is within ~0.3-0.5 mS/cm of input. Then water to 10-20% runoff each time. This treats the medium, not the plant; it is not a pre-harvest flush, which is a myth.
- Recovery: Runoff EC tracks input at the next 2-3 waterings; new leaves stop burning.
- Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.
- Confirm: Pour-through extraction for container pH and EC: Water normally, wait 30 minutes to 2 hours, pour enough pH-adjusted water on top to collect about 50 mL of leachate (roughly 75 mL for a 15 cm pot, 150 mL for a 4 L pot, 350 mL for 11 L), and measure pH and EC of that 50 mL. Less disruptive than full runoff and more repeatable.
- Confirm: Slurry (1:2) test of the medium: Take a sample from the root zone (not the top 2 cm), mix 1 part medium with 2 parts distilled water by volume, stir, wait 30 minutes and measure pH and EC of the liquid. Use it for soil and living soil where runoff is unreliable. Slurry EC reads lower than pour-through EC; compare like with like.
- Article: [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)

### Copper toxicity (copper sprays, ionisers, pipework) (Less likely)

- Kind: Too much of something; urgency: Deal with it this week
- Fix: Stop copper fungicides and ionisers, replace copper pipework contact; change the reservoir. Keep Cu at about 0.03-0.1 mg/L.
- Recovery: New white root tips within a week.
- Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
- Confirm: Get a water report (or test your water): Ask your water utility for the annual report or test well water: alkalinity (mg/L CaCO3), pH, EC, Ca, Mg, Na, Cl, B, and whether it uses chlorine or chloramine. Alkalinity above ~100-150 mg/L as CaCO3 pushes root-zone pH up; sodium above ~50 mg/L and chloride above ~70 mg/L are a problem; softened water is high in sodium.
- Article: [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md)

### Ammonium toxicity (too much NH4 in the feed) (Less likely)

- Kind: Too much of something; urgency: Deal with it this week
- Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH.
- Recovery: pH stops falling and new leaves lose the dark claw within a week.
- Confirm: Measure input pH and root-zone (runoff or reservoir) pH: Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
- Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
- Article: [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md)

### Boron deficiency (Less likely)

- Kind: Nutrient; urgency: Deal with it this week
- Fix: Rule out broad mites first. Supply about 0.2-0.5 mg/L B (boric acid ~1.1-2.9 mg/L, or a complete micro mix). The gap between enough and too much is narrow: never add B 'just in case' on top of a complete feed.
- Recovery: New shoots grow normally from the tip or from side buds within 10-14 days.
- Confirm: Magnifier check of leaf undersides and new growth: Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
- Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
- Confirm: Leaf tissue analysis: Send 20-30 most-recently-matured leaves (no petioles) from affected plants, and separately from healthy ones, to an agricultural lab. Compare with cannabis and hemp sufficiency ranges (for example N 3.3-4.8%, Mg 0.40-0.81%, K 1.8-2.9% dry weight in recent mature leaves). Results take 1-2 weeks; use it to confirm a chronic problem, not an emergency.
- Article: [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md)

## Note

Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.