What are the most common causes of brown tips and leaf edges?
Brown tips and edges are not a single-cause symptom — they are the leaf's response to several types of stress that damage cells along the leaf margin. The four most common causes are: salt burn (EC too high), cationic antagonism where excess potassium blocks calcium uptake, VPD running too high which forces stomata to close and creates water stress, and salt buildup in the substrate from insufficient flushing. Before making any changes, you need to figure out which one you're dealing with.
How do you tell salt burn from other causes?
Salt burn starts at the tips of older leaves and moves toward the edges. The damage is symmetrical: if a leaf has brown tips on both sides of the apex, salts are the main suspect. On the other hand, if the damage is asymmetrical, appears as irregular spots, or spreads quickly toward the interior of the leaf, you may be looking at fungal issues, light burn, or active calcium deficiency.
- Symmetrical tips on older leaves → salt burn, EC too high
- Brown edges moving inward → check Ca and K before drawing conclusions
- Damage on new growth → more likely Ca deficiency or light burn
- Symptoms throughout the whole plant at once → possible nutrient lockout from pH, not a simple deficiency
What does excess potassium do and how do you spot it?
Potassium, calcium, and magnesium compete for the same uptake sites on the root membrane. When K runs too high, it displaces Ca²⁺ and Mg²⁺: the plant shows cal-mag deficiency symptoms even though those nutrients are present in solution. Bevan, Jones & Zheng (2021) documented this antagonism in hydroponic cannabis and found that excess K during flowering is one of the most common grower errors. The red flag is K above roughly 175 ppm combined with calcium deficiency symptoms on new growth.
What is the diagnostic protocol before changing anything?
- 1. Measure your feed solution EC. If it's above the target range for your growth stage, that alone is enough to explain the tip burn.
- 2. Measure runoff EC. If runoff EC is higher than your feed EC, there is salt buildup in the substrate.
- 3. Check pH. Outside the 5.5–6.5 range, Ca and Mg get locked out even with a correct EC (Veazie et al. 2025).
- 4. Identify which leaves are affected. Older leaves point to salt burn or high K; new growth points to active calcium deficiency.
- 5. Do not add nutrients until you complete this diagnosis. Raising EC will make the burn worse.
How do you correct salt burn, step by step?
Once you confirm high EC or salt accumulation, the fix is to lower the concentration and flush the substrate:
- Drop your feed EC to the low end of your stage's target range: 0.8–1.2 mS/cm in veg, 1.2–1.8 mS/cm in early bloom.
- In soil or coco, flush with plain water at EC 0.0–0.4 and correct pH until runoff comes down to your target.
- In hydro, do a partial or full reservoir change.
- Once EC is corrected, wait 4–7 days before assessing whether new symptoms stop appearing. Tissue that is already damaged will not recover.
Does excess fertilizer always burn? How do you prevent it?
Salt burn happens when the ion concentration in solution exceeds what the plant can handle. Dialing in your feed rate to match growth stage and plant size — without systematic overfeeding — is the practice that keeps EC from climbing above verified ranges. It is not a guarantee, because EC also shifts with evapotranspiration and substrate temperature, but keeping your solution within peer-reviewed ranges is the most reliable starting point.
When can high VPD mimic salt burn?
A VPD above 1.6 kPa forces stomata to close to conserve water. Transpiration stops, mass-flow nutrient delivery shuts down, and the leaf margins — last in line for water — die back from the outside in. The visual result looks a lot like salt burn: brown edges, crispy tips, leaves curling upward. The key difference: if EC is in range and runoff EC is also normal, check temperature and relative humidity before touching your feed solution.
