Why does my arrowhead plant have brown spots?

The 4 most likely causes

The cause of arrowhead plant brown spots usually narrows to one of the items below, ranked by how often we see each in Growli's diagnostic chats. Work down the list — most readers find their answer in the top two.

1. Low humidity (Likely)
   Arrowhead plant is native to humid environments and struggles when household humidity drops below 40%. The first sign is crispy brown leaf tips, followed by pale, curling foliage. A humidifier, a pebble tray, or grouping plants together raises local humidity meaningfully.
2. Fluoride or chlorine in tap water (Likely)
   Arrowhead plant is sensitive to the fluoride and chlorine added to most municipal water supplies. Minerals build up at the leaf tips and cause crispy brown edges or speckled spots. Switch to rainwater, filtered water, or tap water that has sat uncovered for 24 hours so the chlorine can off-gas.
3. Fungal or bacterial leaf spot (Possible)
   Brown spots with yellow halos appearing on arrowhead plant, especially after water sat on the leaves overnight, are most often fungal or bacterial leaf spot. Remove affected leaves, water only at the soil line, improve airflow, and apply a copper fungicide if it spreads.
4. Sunburn or intense direct sun (Possible)
   Bleached patches, papery brown spots, or crisped leaf surfaces on the south-facing side of arrowhead plant are sunburn. Acclimatise it more gradually after a move, or filter midday sun with a sheer curtain. Sunburn damage doesn't heal — wait for new growth.

Why arrowhead plant in particular

Grown for filtered understorey light, an arrowhead scorches pale, papery patches onto its most exposed leaves if it is moved abruptly into direct sun. A different, telltale problem for this species is bacterial leaf spot: watersoaked patches that start between the veins, yellow, then blacken and spread where warm, wet air lingers on the foliage. Sun damage sits on the sunniest leaves, while the bacterial version looks greasy at first and peppers the growth more randomly across the plant.

Normal turnover, or real trouble?

Not every mark is disease. A dry, static tan patch where a leaf was knocked, creased in transit, or brushed a cold pane simply scars and never enlarges. What deserves attention is any spot that is actively expanding, especially one ringed by a yellow halo or looking wet and greasy at its edge in warm, still, humid air, since that is spreading rather than a healed injury the leaf has already walled off.

How to diagnose in 60 seconds

Run these quick checks before you change anything — the right fix depends on what you find.

• Are the spots dry and crisp or wet and spreading? Crisp = sunburn, fluoride, or old damage; wet = active fungal or bacterial spot.
• Do the spots have a yellow halo? Halos are classic for bacterial and fungal leaf spot.
• Are they only on the sunny side of the plant? That points to sunburn.
• Are the leaf tips uniformly brown while the rest is healthy? Crispy tips on arrowhead plant usually mean low humidity or tap-water minerals.

The fix — step by step

Act by taking the leaf off, not by feeding or misting. Snip away each spotted leaf at its base with clean scissors, move the plant somewhere brighter and better ventilated, and above all keep water off the remaining foliage — wipe leaves dry if you splash them and never leave beads sitting overnight, because still moisture on the leaf is exactly what lets these spots spread across an arrowhead.

This is the recovery sequence Growli walks users through for arrowhead plant with brown spots. Work through the steps in order; skipping ahead is the most common reason a plant fails to bounce back.

1. Quarantine if you suspect disease. If spots look wet, are spreading, or have a yellow halo, move arrowhead plant away from your other plants until you have a diagnosis. Disinfect your tools between plants.
2. Remove the worst-affected leaves. Snip off heavily spotted leaves at the base. Don't compost them — bag and bin to stop spore spread. Never remove more than 30% of foliage in one go.
3. Switch to filtered or rain water. If you suspect tap-water damage, water with rainwater, distilled water, or tap water that has stood uncovered for 24 hours. Continue for 4-6 weeks before re-evaluating.
4. Improve airflow and watering technique. Water at the soil line only — never on the leaves. Space arrowhead plant so leaves are not touching neighbouring plants. A small fan in stagnant rooms makes a surprising difference.
5. Apply a treatment if needed. For active fungal spread, a copper-based fungicide applied weekly per the label is the standard remedy. For sunburn or fluoride damage, no treatment helps — just remove damaged leaves and wait for new growth.

When this can't be saved

Most cases of arrowhead plant brown spots are recoverable, but a few red flags point to a plant that has gone past the point of return. If you spot any of these, consider propagating a clean cutting and starting over.

• Spots are spreading by several per day across multiple leaves — active aggressive disease.
• The whole crown of the plant is blackening from a central point outward.
• Healthy-looking neighbouring plants are starting to show the same symptoms.

Prevention

For arrowhead plant, the single biggest preventative is matching its native rhythm: when the top half of the soil is dry, every 7-10 days, medium to bright indirect light, and a free-draining pot with a working drainage hole. Water at the soil line, not the leaves, especially in the evening when leaves can't dry before nightfall. Switch to filtered or collected rainwater for sensitive species — it pays for itself in fewer crispy edges. Improve airflow around densely planted shelves with a small clip-on fan.

Common questions

Related guides

• What's wrong with my plant? — the diagnosis apps compared
• Is arrowhead plant toxic to cats and dogs? — toxic to pets, per the ASPCA
• How often to water arrowhead plant — the watering brief
• When to repot arrowhead plant — pot size and timing
• Brown spots on plants — the full diagnostic guide across species
• What's wrong with my plant? — Growli's flagship diagnosis index
• Arrowhead plant — yellow leaves
• Arrowhead plant — curling leaves
• Arrowhead plant — drooping
• Monstera — brown spots