Pepper blossom-end rot: cause and fix

TL;DR - Quick fix

Brown, sunken, waterlogged spots on the bottom of your peppers are blossom-end rot, caused by irregular watering and calcium deficiency. This is NOT a disease - it's physiological. The pepper grows faster than calcium can be absorbed. Solution: water regularly (never too dry, never waterlogged) and add lime (limestone or gypsum).

What is blossom-end rot?

Blossom-end rot looks terrible - brown or black, mushy spots on the bottom end of your peppers. It starts small and grows into a sunken, waterlogged patch. Eventually the fruit becomes inedible.

This is NOT fungus, NOT bacteria, NOT virus. It is purely physiological - about calcium in the plant. Peppers grow faster than their root systems can absorb and transport calcium. When a certain growth moment arrives - usually during heavy fruit-setting - the bottom of the fruit cannot fill with mineral fast enough. Cells rupture. Brown material spreads.

This problem especially affects:

• Tomatoes (very sensitive)
• Peppers (sensitive)
• Eggplants (sometimes)
• Melons and pumpkins (rare)

Cause: Irregular watering

The real culprit is water. Remember: calcium travels in plant sap from root to leaf and fruit. If your plant dries out and then suddenly gets lots of water, everything skips ahead. Water is absorbed, growth accelerates, but calcium lags behind.

What happens:

1. Plant is dry (root sits without water, uptake stops)
2. You give lots of water (plant drinks greedily)
3. Growth shoots up, leaves grow fast
4. But: calcium transport is delayed
5. Young fruits get too little calcium
6. Cells die off at the bottom of the fruit

Especially pot soil is vulnerable here. Pot soil dries out fast. Garden soil can hold moisture longer - but it happens there too.

Cause: Low lime in soil

The second cause is lime-poor soil. Peppers need a lot of calcium. If your soil has only 200 mg/liter calcium (many Dutch soils), that is too low. Peppers want 400-500 mg/liter.

Dutch compost usually has LITTLE lime baked in. Potting soil is often acidic (pH 5-6). Garden soil can be the same pH. Without lime, roots cannot absorb enough calcium - even if you water regularly.

Check your soil:

• Low-lime soils are acidic (pH < 6)
• Many Dutch soils are naturally acidic (sandy soils especially)
• Peat compost (common in potting mixes) is VERY acidic and calcium-poor

How to prevent blossom-end rot

Rule 1: Water regularly and evenly

This is the most important. Not dry, not wet - moist. Check daily.

In pot soil:

• Check 5 cm deep in pot daily
• If feels dry, water (but don't flood)
• In hot summers you may need to water twice daily

In garden:

• Peppers need 20-30 mm water per week in July-August
• Distribute evenly: water 3x per week lightly better than once heavily
• Add mulch (5 cm compost) helps retain water

Rule 2: Ensure enough lime

Option A: Add lime immediately (potting soil)

• Mix before planting: 5-10 grams ground limestone per liter of potting soil
• Or: 3-5 grams gypsum per liter
• Mix thoroughly before planting

Option B: Add lime later (garden or growing plant)

• Sprinkle 100-200 grams ground limestone around your plant
• Work lightly into top 5 cm of soil
• Repeat every 4 weeks
• Or: 50-100 grams gypsum around plant, work in lightly

Option C: Foliar spray

• Works faster than root work
• Spray leaf undersides with calcium chloride (1%) or gypsum suspension (2%)
• 1x per week, early morning
• Fills small gaps quickly

Rule 3: Fix acidic soils for pH

If your soil is acidic (pH 5-5.5):

• Calcium is poorly absorbed, even if you give lots
• Add lime until pH rises to 6-6.5
• Check with pH test kit
• Wait 2 weeks after liming before planting

What to do with already-affected fruit

Bad news: fruit already rotting cannot be saved. The cells are dead. It does not look better.

Good news: you can eat most of it. Cut off the brown bottom. The inside is usually fine. Use in soup, stew, or vegetable dishes.

Step-by-step

Step 1: Fix your watering

Check your watering routine. Pot should feel moist (gently squeeze top soil). Never dry, never soggy.

Step 2: Check pH and add lime

Test your soil pH with a kit from the garden center. Below pH 6? Sprinkle limestone around your plant. Work in, water well.

Step 3: Spray leaves weekly with calcium

Take gypsum or calcium chloride (1-2%). Spray leaf undersides every 7 days, early morning. Helps the plant absorb calcium faster.

Step 4: Mulch around the plant

Lay 5 cm compost/mulch around your pepper. This regulates moisture and adds extra calcium as it breaks down.

Step 5: Harvest carefully

Check every 3 days for new fruit. Do you see red starting? Begin intense water management. The earlier, the better.

Frequently asked questions

Can I do anything if the fruit already has rot?

No. Once affected, stays affected. Cut off the red bottom and use the flesh. Or: pick the pepper green (a little earlier) and let it ripen at home. The red spot does not spread further once picked.

Is blossom-end rot contagious to other plants?

No, it is not contagious. It is physiological. Other vegetables around your pepper can also develop this problem (tomatoes especially), but not because your pepper has it - because THEY are also calcium-sensitive.

Does limewash or milk help?

Yes, a little. Limewash contains dissolved calcium. Watering 1x per week with diluted milk/limewash helps mildly. But it does not solve irregular watering. You MUST first fix watering routine.

How do I recognise calcium deficiency on leaves?

Pepper leaves rarely show visible calcium deficiency. Tomatoes do - they get small holes in young leaves. Peppers show it first on fruit (blossom-end rot). So this is your warning: calcium is running low.

Is it better to grow peppers in garden than in pots?

Yes. Garden soil (with regular moisture) is more stable for watering. Potting soil dries out MUCH faster. Plant peppers in large pots (at least 15 liters) and mulch to retain moisture. Or: plant in garden (much better).

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