Tomato Diseases: How To Fight Blossom-End Rot

by Matt Gibson (revised and updated)

The 30-second version: Blossom-end rot isn’t a disease and it isn’t contagious. It’s a calcium problem inside the fruit — and that’s almost always caused by uneven watering, not by a lack of calcium in your soil. Fix your watering, mulch to hold moisture steady, and stop reaching for the eggshells and Epsom salt. Here’s how.

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Do these three things today

1. Water deeply and on a consistent schedule — never let the soil swing from bone-dry to soaked. This is the single most important fix.
2. Mulch around your plants to hold soil moisture steady between waterings.
3. Stop over-fertilizing, especially with high-nitrogen feeds, which make the problem worse.

Now the details.

What Blossom-End Rot Is (and Isn’t)

When the growing season starts out rainy and then shifts to dry conditions just as fruit is setting, watch out for blossom-end rot. When tomatoes are about half their mature size, you’ll see large water-soaked areas on the bottom of the fruit that quickly enlarge and turn dark brown and leathery. Those areas are rotting, so the affected fruit has to be picked and discarded.

The spots appear at the blossom end of the fruit — the bottom, opposite the stem — which is where the condition gets its name. Despite the word “rot,” blossom-end rot is not a disease. It’s a physiological disorder caused by a calcium imbalance in the developing fruit. It shows up in tomatoes most often, but also affects peppers, eggplant, melons, and squash.

Because it isn’t caused by a virus, fungus, or bacteria, blossom-end rot does not spread from plant to plant. You don’t need to pull affected plants — just remove the bad fruit and fix the underlying conditions.

What Actually Causes It

Here’s the part most articles get wrong: the problem usually isn’t that your soil lacks calcium. Most garden soil has plenty. The problem is that the plant can’t move enough calcium into the fruit fast enough — and that’s almost always a watering problem.

Calcium travels through the plant dissolved in water. When watering is inconsistent — a dry spell followed by a soaking, or a wet spring followed by a dry fruit-set — the plant can’t deliver a steady calcium supply to the fastest-growing tissue, which is the bottom of the fruit. The tissue there breaks down, and you get the rot.

Conditions that trigger or worsen it:

• uneven watering (the big one) — drought followed by heavy watering
• heavy rainfall or overwatering
• root damage from hoeing or cultivating too close to the plant
• soil pH that’s too high or too low (aim for around 6.5)
• cold soil early in the season, which slows nutrient uptake
• soil high in salts
• fast-climbing temperatures or extreme heat
• excess nitrogen early in the plant’s life, which pushes rapid leafy growth that outpaces calcium delivery

Note that paste and Roma-type tomatoes — San Marzano, Amish Paste, Roma — are far more prone to blossom-end rot than round slicing or cherry types. If you grow paste tomatoes, watering consistency matters even more.

What Symptoms Look Like

Blossom-end rot usually shows up while the fruit is still green or ripening. It starts as a small, water-soaked, sunken area on the bottom of the fruit. That spot enlarges, sinks further, and turns dark, leathery-brown or black. Left alone, it can cover the entire lower half of the tomato, which goes flat or concave and is ruined.

Don’t Mistake It for Something Else

Several other tomato problems get misdiagnosed as blossom-end rot. Before you treat, make sure that’s what you’ve got:

• Sunscald — pale, papery, blistered patches on the side of the fruit facing the sun, usually after leaves were lost or over-pruned. Not on the bottom.
• Anthracnose — sunken, circular, water-soaked spots on ripe fruit, often with concentric rings; this one is a fungal disease and can spread.
• Fruitworm or hornworm damage — actual holes or chewed areas, often with frass (insect droppings) nearby.

If the damage is a sunken brown patch specifically on the blossom (bottom) end, it’s blossom-end rot.

How to Treat and Prevent It

You can’t save fruit that’s already affected — remove and discard it so the plant stops spending energy on it. But you can absolutely correct the conditions so future fruit comes in clean. With consistent care, plants typically recover in a few weeks, so don’t be discouraged if you don’t see results overnight.

Water consistently — this is 90% of the fix. Don’t let the soil dry out completely between waterings, and don’t swing from drought to flood. Aim for roughly one inch of water per week, delivered deeply (to about six inches) rather than in frequent light sprinklings. In hot, dry spells you may need to water more often. If you get heavy rain, make sure beds drain well so roots aren’t waterlogged.

Mulch. A layer of organic mulch is one of the most effective things you can do, because it buffers soil moisture and keeps it from spiking and crashing. (See our Guide to Using Mulch the Right Way.)

Protect the roots. Avoid hoeing, chopping, or cultivating close to the plant — damaged feeder roots can’t take up water and calcium. Staking young plants helps keep them stable.

Go easy on nitrogen. Don’t over-fertilize during early fruiting, when blossom-end rot is most likely. Use a fertilizer that’s low in nitrogen and high in phosphorus, such as a 4-12-4 or 5-20-5 blend. Avoid ammoniacal-nitrogen fertilizers, which can actually trigger flare-ups; nitrate-based nitrogen is gentler.

Get the soil right before planting. Test your soil and keep the pH around 6.5 (how to test your soil’s pH). If your soil is genuinely calcium-deficient, add lime (which also raises pH) or gypsum (which doesn’t) before or at planting — that’s a long-term fix, not an in-season rescue. If your soil is cold at planting time, wait for it to warm up before setting out tomatoes.

A note on the popular “cures” — most don’t work

Gardening forums are full of quick fixes for blossom-end rot. Here’s the honest rundown:

• Eggshells release calcium far too slowly to help the current crop — they take months to break down. Fine as a long-term soil amendment, useless as an emergency treatment for the rot.
• Powdered milk is often recommended as a faster calcium source. Some gardeners report success, but the evidence is thin, and if your watering is inconsistent it won’t matter how much calcium you add.
• Foliar calcium sprays are widely sold for it, but research shows very little calcium actually reaches the fruit through the leaves. Don’t count on them.
• Epsom salt makes it worse. Epsom salt is magnesium sulfate — it contains no calcium at all, and the magnesium it adds competes with calcium for uptake into the roots. Skip it.
• TUMS are sometimes suggested as a calcium tablet for the soil. You’d need an impractical amount to make a difference. Not a real solution.

The takeaway: it’s the watering, not the eggshells.

Common Questions

Can you eat a tomato with blossom-end rot? Yes — cut away the rotted portion and the rest is safe to eat. But affected tomatoes are often mealy and bland, and you shouldn’t can or preserve them.

Should I remove tomatoes with blossom-end rot? Yes. They won’t recover, and removing them lets the plant put its energy into healthy new fruit.

Does blossom-end rot affect the whole plant? No — symptoms appear only on the fruit. That said, the cause can be in the roots: an underdeveloped or damaged root system may fail to take up enough water and calcium, which then shows up as blossom-end rot in the fruit.

Does it spread between plants? No. It’s not contagious because it isn’t a pathogen. If several plants have it, that points to a shared condition — usually watering — not an infection passing between them.

Which plants get blossom-end rot? Tomatoes most commonly, plus peppers, eggplant, melons, squash and other cucurbits.

Want to learn more about how to fight tomato blossom-end rot?

North Dakota State University covers The Epsom Salt Myth

The Old Farmer’s Almanac covers Blossom-End Rot

Better Homes & Gardens covers 6 Common Tomato Troubles and How to Fix Them

Bonnie Plants covers Conquer Blossom End Rot