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Few things are more heartbreaking than watching your beautiful, almost-ripe tomatoes develop gross, dark, sunken spots on the bottom.
You’ve waited WEEKS. You’ve babied these plants. And now—right before harvest—they’re rotting from the bottom up.
That’s blossom end rot, and it’s one of the most common (and most frustrating) tomato problems. But here’s the good news: It’s preventable and fixable.
Let me explain what it is, why it happens, and exactly how to stop it.
## What Is Blossom End Rot?
Blossom end rot (BER) is a dark, leathery, sunken spot that forms on the bottom (blossom end) of tomatoes, peppers, and squash.
It starts small: A water-soaked spot on the blossom end
It grows: The spot turns tan, then brown, then black
It becomes leathery: The tissue dies and becomes sunken and dry
Secondary rot: Fungus or bacteria often invade the dead tissue, causing full fruit rot
Important: Blossom end rot is NOT a disease. It’s a physiological disorder caused by calcium deficiency in the developing fruit.
## What Causes Blossom End Rot?
Here’s where it gets interesting: It’s RARELY because your soil lacks calcium.
Most soils have plenty of calcium. The problem is that the plant can’t deliver calcium to the fruit fast enough.
Why?
Because calcium travels through the plant in water. When water uptake is inconsistent, calcium can’t reach the developing fruit. The cells at the blossom end literally collapse from calcium deficiency.
### The #1 Cause: Inconsistent Watering
This is the culprit 90% of the time.
What happens:
– You water deeply one week
– Forget for a few days, soil dries out
– Water again
– Repeat this cycle
Result: The plant can’t uptake calcium consistently, and developing fruit suffers.
Tomatoes that go through wet-dry cycles are HIGHLY prone to BER.
### Other Causes:
1. Overwatering
Constantly soggy soil suffocates roots, preventing calcium uptake.
2. Root damage
Damaged roots can’t uptake water and calcium effectively.
3. Excessive nitrogen
Too much nitrogen causes rapid growth that outpaces calcium delivery.
4. Soil pH too low or too high
Calcium availability is reduced if pH is below 6.0 or above 7.5.
5. High salts in soil
Competes with calcium uptake.
6. Rapid fruit growth during hot weather
Fruit grows so fast that calcium can’t keep up.
7. Actual calcium deficiency in soil
This is RARE, but possible in sandy, acidic, or heavily leached soils.
## How to Fix Blossom End Rot (Once It Starts)
Bad news: You can’t fix fruit that already has BER. The damage is done. Remove affected fruit and focus on preventing it in future fruit.
Good news: New fruit forming on the same plant WON’T necessarily get BER if you address the underlying cause.
What to do:
### 1. Remove Affected Fruit
Pick off tomatoes with BER. They won’t recover, and leaving them on the plant wastes energy.
Can you eat them? Yes! Cut off the bad spot and eat the rest. It’s not dangerous, just ugly.
### 2. Water Consistently (THE MOST IMPORTANT STEP)
This is your #1 fix.
How to water properly:
– Water deeply, 1-2 times per week (or more in hot weather)
– Keep soil consistently moist (not wet, not dry)
– Stick your finger 2 inches into soil—if dry, water. If damp, wait.
– Use drip irrigation or soaker hoses for even moisture
– Avoid “wet Monday, dry Thursday, soaked Saturday” cycles
Mulch heavily: 2-3 inches of straw, leaves, or wood chips keeps moisture consistent.
### 3. Add Calcium (If Needed)
If you’ve been watering consistently and still see BER, add calcium.
How to add calcium:
Option 1: Lime (raises pH)
– Use if soil pH is below 6.5
– Work into soil around plants
– Takes weeks to become available
Option 2: Gypsum (doesn’t raise pH)
– Use if soil pH is already 6.5-7.0
– Adds calcium + sulfur
– Work into soil, water in well
Option 3: Calcium spray (fast-acting)
– Spray leaves and fruit with calcium chloride solution
– Provides immediate calcium boost
– Repeat weekly during fruiting
Option 4: Crushed eggshells
– Slow-release calcium
– Work into soil (takes months to break down)
– More preventative than curative
Option 5: Bone meal
– Adds calcium + phosphorus
– Work into soil at planting or side-dress
How much: Follow package directions. Don’t just dump random amounts—you can create nutrient imbalances.
### 4. Check and Adjust pH
Test your soil pH. Tomatoes prefer 6.0-6.8.
If pH is too low (acidic): Add lime
If pH is too high (alkaline): Add sulfur or acidic compost
### 5. Stop Over-Fertilizing
If you’ve been feeding heavily (especially with nitrogen), stop. Let the plant balance out.
Excess nitrogen causes rapid leafy growth that outcompetes fruit for calcium.
### 6. Don’t Damage Roots
Avoid deep cultivation near plants. Be gentle when weeding. Damaged roots = poor water/calcium uptake.
## How to Prevent Blossom End Rot
Prevention is way easier than treatment.
### 1. Water Consistently
Can’t stress this enough. Even, consistent moisture is the #1 prevention strategy.
– Mulch heavily
– Water deeply but infrequently
– Use drip irrigation or soaker hoses
– Check soil moisture daily during hot weather
### 2. Prepare Soil Before Planting
Test soil pH and adjust to 6.0-6.8
Add calcium at planting:
– Work lime or gypsum into planting holes
– Mix in bone meal
– Add compost (contains trace calcium)
### 3. Choose Resistant Varieties
Some tomatoes are more prone to BER than others.
More susceptible:
– Large paste tomatoes (Roma, San Marzano)
– Large slicers (Beefsteak types)
– Early fruit on any variety
More resistant:
– Cherry tomatoes
– Small to medium varieties
– Disease-resistant hybrids often have better calcium uptake
### 4. Don’t Over-Fertilize
Follow fertilizer directions. More isn’t better.
Use balanced fertilizer early, then lower nitrogen formula during fruiting.
### 5. Mulch Heavily
I’ll say it again: Mulch is your best friend.
2-3 inches of organic mulch:
– Keeps soil moisture even
– Regulates soil temperature
– Prevents moisture fluctuations
### 6. Avoid Overhead Watering
Water at soil level. Overhead watering (sprinklers) is inconsistent and promotes disease.
### 7. Plant at the Right Time
Planting too early (in cold soil) stresses plants and can lead to BER on early fruit.
Wait until soil is warm and nights are consistently above 50°F.
## Why Does BER Affect Some Fruit But Not Others?
You might notice BER on your first fruits but not later ones. Why?
Early season stress: Plants are adjusting to outdoor conditions, roots aren’t fully established, watering might be inconsistent early on.
Hot weather: Rapid growth during heat waves outpaces calcium delivery.
Once conditions stabilize (established roots, consistent care, moderate temps), BER often stops appearing on new fruit.
## Common Myths About Blossom End Rot
Myth #1: It’s a fungus or disease
Nope! It’s a physiological disorder (calcium deficiency in fruit). Not contagious.
Myth #2: You need to add calcium
Maybe, but probably not. Most soils have enough calcium. The issue is usually water uptake.
Myth #3: Epsom salt fixes it
No. Epsom salt is magnesium sulfate. It doesn’t contain calcium. This myth needs to die.
Myth #4: Baking soda helps
No. Baking soda doesn’t add calcium and can harm plants.
Myth #5: Eggshells placed around plants cure it
Eggshells take MONTHS to break down and release calcium. They’re preventative at best, not a quick fix.
Myth #6: It only affects certain varieties
Any variety can get BER if conditions are right (or wrong). Some are just more susceptible.
## BER on Different Tomato Types
Large slicers and paste tomatoes: Most susceptible. Large fruit requires more calcium.
Cherry tomatoes: Less susceptible. Smaller fruit requires less calcium.
First fruits of the season: Most at risk. Plants are still establishing roots.
Late season fruit: Usually fine once plants are established and conditions stabilize.
## What If You’ve Done Everything and Still Get BER?
Sometimes BER happens even with perfect care. Don’t beat yourself up.
Possible reasons:
– Extreme heat wave (rapid fruit growth)
– Your specific soil chemistry
– Variety is just prone to it
– Weird weather patterns
What to do:
– Keep doing what you’re doing (consistent water, adequate calcium)
– Remove affected fruit so plant focuses on new fruit
– Next year, try different varieties
– Consider growing in containers with fresh soil
## The Bottom Line
Blossom end rot looks scary, but it’s fixable.
The 3-step fix:
1. Water consistently (this is 90% of the solution)
2. Mulch heavily (helps maintain consistent moisture)
3. Add calcium if needed (gypsum or lime, depending on pH)
Prevention checklist:
✅ Consistent watering (most important!)
✅ Mulch 2-3 inches deep
✅ Test and adjust soil pH to 6.0-6.8
✅ Add calcium at planting (bone meal, lime, or gypsum)
✅ Don’t over-fertilize with nitrogen
✅ Avoid root damage
✅ Choose less susceptible varieties
Most gardeners see BER early in the season and then it disappears as conditions stabilize. Don’t panic. Adjust your care, and new fruit will be fine.
And remember: even if you lose a few tomatoes to BER, you’ll still have plenty left. Tomatoes are prolific!
Now go check your soil moisture! 🍅
