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Blossom end rot is a calcium problem inside the fruit, not usually a calcium problem in your soil, and fixing your watering routine instead of dumping in eggshells is what actually clears it up within a week or two. If you’ve been staring at a black, leathery patch on the bottom of your tomatoes and wondering what you did wrong, the short answer is probably nothing serious. You just need to get water moving through that plant more evenly, and I’ll walk you through exactly how.
What Blossom End Rot Looks Like
Blossom end rot starts as a small, water-soaked spot on the bottom of a developing tomato, opposite the stem, and it darkens into a sunken, leathery brown or black patch as the fruit grows. Blossom end rot (often shortened to BER) is a physiological disorder, meaning it’s caused by a breakdown inside the plant’s own systems rather than by a fungus, bacteria, or pest. That’s good news. It won’t spread to other plants and it isn’t a disease you need to treat with anything.
You’ll usually spot it first on the earliest fruits of the season, while they’re still green and about a third to half grown. The lesion doesn’t stay small. Left alone, it can eventually take over most of the bottom half of the tomato, and the damaged skin gives bacteria and mold an easy way in, so affected fruit rots faster than healthy fruit around it.
The Real Cause of Blossom End Rot
Blossom end rot happens because calcium isn’t reaching the developing fruit fast enough, and that’s almost always a water problem, not a shortage of calcium in your soil. Calcium doesn’t move through a tomato plant the way nitrogen or potassium does. Those nutrients can relocate to wherever the plant needs them most. Calcium can’t. It only travels through the plant dissolved in water moving up through the roots, and once it’s deposited in a leaf or a stem, it stays there. It doesn’t get redistributed to the fruit later.
Fruit sits at the end of that water supply line, and it’s also the part of the plant that transpires the least, so it’s the first thing to come up short when water uptake slows down or turns uneven. If your soil dries out for even a few days during that critical fruit-growth window, or the water supply is interrupted some other way, the calcium already in your soil never makes it to where it’s needed. You can have plenty of calcium in the ground and still get blossom end rot, and honestly, most home gardens do have enough calcium already. The deficiency is in the fruit, not the soil.
Why It Seems to Show Up Out of Nowhere
Blossom end rot tends to appear right after a stretch of hot, dry weather, or after a dry spell gets broken by a heavy soak or a big rainstorm. That swing between drought stress and sudden abundance is exactly what interrupts steady calcium movement. A few other things create the same kind of interruption.
Containers dry out faster than garden soil because there’s less volume holding moisture, so container-grown tomatoes are hit harder and more often. Compacted or heavy clay soil restricts root growth, which limits how much water the plant can pull up in the first place. Waterlogged or poorly draining soil suffocates roots and stops them working properly too, so it’s not just about underwatering. Rough handling during transplanting, or aggressive cultivation too close to the root zone, can snap fine feeder roots and slow water uptake for days. And a heavy dose of nitrogen fertilizer right as fruit is setting pushes the plant into a burst of leafy growth that competes hard with the fruit for the water and calcium that’s available.
I grow several tomato varieties in raised beds and I still get caught out most summers during our first real heat wave, usually because I’m watering on the same schedule I used in cooler weather. The fix isn’t complicated once you know to look for it. You just have to catch the gap between what the weather’s doing and what your watering can is doing.
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Skip the Eggshells, Tums, and Epsom Salt
Crushed eggshells, antacid tablets, and Epsom salt don’t fix blossom end rot, and Epsom salt can actually make it worse. These are the three remedies you’ll see recommended most often, and all three miss the actual problem.
Eggshells do carry calcium, but they break down far too slowly to reach the fruit that’s rotting on your plant right now. By the time they’ve decomposed enough to release usable calcium, that season’s affected fruit is long gone. They’re genuinely good for your soil over the long haul, so keep adding them to your compost, just don’t expect them to solve this year’s problem.
Antacid tablets work on the same flawed logic. Even if the calcium they add were available fast enough, the plant still can’t move it to the fruit without consistent water.
Epsom salt is magnesium sulfate and contains no calcium at all, and adding it can actively compete with the calcium your plant already has, making uptake worse. Magnesium and calcium share the same uptake pathway into the plant, so flooding the soil with magnesium can crowd calcium out. Save your Epsom salt for your own bath after a long day in the garden. It won’t help your tomatoes.
How to Stop Blossom End Rot in a Week or Two
Water your tomatoes consistently, mulch heavily, and ease off the nitrogen, and you should see clean, healthy fruit again within 7 to 14 days. Here’s the actual routine.
Water deeply and on a regular schedule rather than little and often. Established tomato plants growing in the ground generally need about 1 to 1.5 inches of water a week, closer to 2 inches during a real heat wave, delivered in fewer, deeper sessions rather than a daily splash. A daily light sprinkle wets the surface and encourages roots to stay shallow, which is the opposite of what you want. Container plants need checking far more often, sometimes daily in hot weather, since potting mix dries out fast.
Check that your watering is actually reaching the root zone. A day or so after watering, push a trowel or your finger about 6 to 12 inches down near the root ball. If it’s dry down there, you’re not watering deeply enough no matter how wet the surface looks.
Mulch is the single biggest lever you have for evening out soil moisture. A 2 to 3 inch layer of straw, shredded leaves, or grass clippings around the base of each plant slows evaporation dramatically and keeps roots cooler, which helps them keep working during heat stress. I mulch mine the same week I plant out, not weeks later, because that early moisture buffer is what gets young plants through their first hot spell without a setback.
If you’re set up for it, drip irrigation on a timer does more than anything else to keep moisture even, since it delivers water slowly and directly to the root zone instead of relying on you remembering. Set it and check soil moisture with your trowel test occasionally to confirm it’s actually working.
Back off high-nitrogen feeding once your plants start setting fruit. Nitrogen is great for building a bushy plant early on, but pushing more leafy growth right as fruit is developing pulls water and calcium away from the tomatoes. A balanced compost top-dress is a gentler option at this stage than a strong nitrogen feed.
Pick off any fruit that’s already showing rot as soon as you spot it. The damage on that individual tomato won’t reverse, and removing it stops the plant wasting energy trying to ripen something you won’t want to eat anyway. Fruit that sets after you’ve corrected your watering should come in clean.
Tomato Varieties More Prone to Blossom End Rot
Roma, San Marzano, and other paste or plum-shaped tomato varieties are more prone to blossom end rot than round slicing types, and determinate varieties tend to be affected more than indeterminate ones. If you grow a mix of varieties and notice your paste tomatoes getting hit hard while your cherry tomatoes stay clean, that’s a real pattern, not bad luck. Paste tomatoes set a large flush of fruit all at once and grow it quickly, which puts a bigger sudden demand on the plant’s water and calcium supply than a slicing variety producing more gradually.
| More prone to BER | Generally more tolerant |
| Roma, San Marzano, and other paste types | Cherry and grape tomatoes |
| Determinate (bush) varieties | Indeterminate (vining) varieties |
| Large-fruited beefsteak types | Smaller, rounder-fruited varieties |
This doesn’t mean skip paste tomatoes. It means if you grow them every year and always seem to lose the first flush, they’re the plants to mulch first, water most consistently, and watch closest during your area’s first hot stretch.
Other Plants That Get Blossom End Rot
Peppers, eggplant, summer squash, cucumbers, and melons can all develop blossom end rot, and the cause and fix are the same as for tomatoes. Peppers are probably the next most common after tomatoes in a home garden, and if you’re seeing BER on your tomatoes during a heat wave, it’s worth checking your pepper plants too since they’re dealing with the same watering stress.
RELATED POST: Why Are There Black Spots on Your Pepper Plants?
FAQs
Can you eat tomatoes with blossom end rot?
Yes, as long as you cut away the affected portion and the rest of the tomato smells and looks normal. Blossom end rot is a physiological disorder, not a pathogen, so the unaffected flesh is safe to eat. If the lesion has already let rot or mold set into the fruit, though, don’t risk it, and compost the tomato instead.
Is blossom end rot caused by overwatering or underwatering?
It’s caused by inconsistent watering rather than strictly too much or too little. Both a dry spell that stresses the plant and a heavy soak or downpour that follows one can interrupt the steady water flow calcium needs to reach the fruit. Waterlogged, poorly draining soil can also trigger it by damaging roots and stopping water uptake altogether.
Will blossom end rot spread to my other tomatoes?
No. Blossom end rot isn’t contagious and won’t spread from one fruit or plant to another, since it isn’t caused by a fungus, bacteria, or pest. If you’re seeing it on multiple fruits or plants at once, that’s because they’re all experiencing the same watering stress, not because the problem is moving between them.
Should I get my soil tested for calcium?
It’s worth doing if blossom end rot keeps coming back even after you’ve fixed your watering, since a genuine soil calcium deficiency is possible, just uncommon. A soil test will also tell you your pH, and tomatoes take up calcium best in soil with a pH between about 6.0 and 6.8. If a test does show low calcium, garden lime worked into the soil in fall or several months ahead of planting is a better fix than anything applied mid-season.
How do I tell blossom end rot apart from other tomato problems?
Blossom end rot always starts at the blossom end, opposite the stem, as a water-soaked spot that darkens and sinks over time. That location and progression are the giveaway. Sunscald shows up on the sun-facing side of the fruit as a pale, blistered patch. Cracking radiates from the stem end, usually after a sudden heavy watering. Fungal issues like anthracnose tend to produce small, sunken, ringed spots that can appear anywhere on the fruit, often closer to ripening.
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