7 Tips to Stop Blossom End Rot and Save the Harvest
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While annoying, blossom end rot (BER) is treatable and preventable. Caught early, your odds of a successful tomato crop are still good. In this post, I’ll talk about blossom end rot causes, prevention and control; plus several photos to help you ID the problem and common mistakes to avoid.
There’s nothing worse than waiting for your first big, beautiful tomato to ripen – only to flip it over and find a black rotten spot on the bottom. (Black tomatoes = tasty, black bottomed tomatoes = not tasty.)
Your black bottomed tomato has blossom end rot.
What causes blossom end rot?
Blossom end rot is caused by the tomato plant not being able to get enough calcium to the developing fruit.
This calcium deficiency is not caused by a plant disease like a fungus or bacteria. (Fungicides and insecticide won’t help.)
Blossom end rot may occur in tomatoes, peppers, melons, eggplants, squash and cucumbers. Some describe it as a “water soaked spot”, but to me, it simply looks black or mushy and rotten.
Why don’t the plants get enough calcium to the fruit?
This can be due to a number of factors, including:
- Moisture – Too little or too much – We’ve had dry conditions this summer. Even with mulch, I have lost some tomatoes to blossom end rot. Last week I heard from two different local friends who had problems with rotten, black bottoms on their tomatoes.
- Too much Nitrogen – Dump a load of fresh manure on your tomatoes, and you may be rewarded with lots of green growth and black bottomed fruit. The nitrogen salts may make the calcium in the soil less available to the tomatoes.
- Soil too Cold at Planting – More of an issue for northern gardeners, cold soil can interfere with nutrient uptake to the plant.
- Root damage due to cultivation – Aggressive digging around your plants (for weed control, for instance) may damage the roots. This would also interfere with nutrient uptake.
- Soil pH too high or too low – Either extreme of pH can make it difficult for your tomatoes to thrive
- Susceptible varieties – Certain tomatoes varieties are more prone to blossom end rot than others.
Does Blossom End Rot Spread?
Blossom end rot does not spread from plant to plant, but plants growing near each other may all be affected, since they share similar growing conditions.
Are tomatoes with BER safe to eat?
If the rot spot isn’t too big, you can trim off the damage and eat the rest of the tomato. Make sure to trim well away from the spot, because the rotten taste can spread beyond the visible damage. (Ask me how I know…)
The tomato below is too far gone to salvage.
How Do You Prevent Blossom End Rot?
Once you see a black or dark brown spot at the blossom end of tomato fruits, they’re a goner. You cannot “heal” a damaged tomato.
Prevention and control measures are where you need to focus to salvage the rest of your tomato season. Here are steps you can take to limit and control blossom end rot on tomatoes and other crops.
1. Maintain steady levels of moisture to your plants.
I use straw mulch to help maintain even soil moisture levels. If rains fail, make sure to give your plants a good soaking 1 to 2 times a week. Stick your fingers in the dirt around the tomato and make sure it’s soaked several inches down.
You can also try water cones or soaker hoses to deliver a slow, steady supply of water. If stuck with heavy rains, trench drainage away from your tomatoes (if possible).
You may also encourage new roots above the sodden ground by heaping compost around the base of the tomato plant. (Roots can drown if the soil is too wet.)
Pot grown plants in particular may be more prone to blossom end rot, due to difficulty keeping the soil moist enough. Try self-watering containers or watering spikes in your container.
2. Use a Balanced Fertilizer.
Aged manure or compost is great, as tomatoes are heavy feeders – just don’t use too much fresh stuff. There are also good organic fertilizers available to help give your plants a jump start.
For detailed planting instructions, see “How to Grow Tomatoes Organically“.
3. Make sure your soil is warm enough, but not too hot.
Tomato seeds need soil temps of at least 60°F (15.6°C) to germinate. Transplants can go into soil above 55°F (13°C), but growth will be slow.
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A general rule of thumb is to wait for nighttime temperatures to be above 55°F. You can easily test your soil temps with a soil thermometer.
To raise soil temperature, you can cover your planting area with black or red plastic – or be patient. In summer heat, organic mulch can keep roots from overheating.
4. Avoid working too close to the roots of the tomato plant.
Pull weeds when you need to, but don’t attack the ground close to the tomato with your hoe. Mulching helps limit the need for cultivation.
5. Check your soil pH before planting.
A soil pH around 6.2 to 6.8 is best for tomatoes. If you need to do a soil test, you can visit “Soil Testing – 5 Easy Tests for Your Yard and Garden” for more information.
Adjust with additional calcium through liming the garden bed to raise the pH.
Lowering pH is best done over time through the use of organic mulches and compost. Leaf compost is particularly effective. (You can use this meter to test both pH and moisture levels.)
6. Add calcium to your soil.
I work in crushed eggshells at planting time. If you don’t have eggshells, try a few cheap calcium antacid tablets.
A handful of garden lime or gypsum also works. Spread a sprinkling of lime onto the soil surface, work in gently, cover with mulch, and water well.
There are also rot stop sprays that can be applied to the tomato foliage.
7. Choose tomato varieties that are less susceptible to blossom end rot.
This is a little tricky, and is a good reason to keep a garden journal. I’ve seen in my own garden that some varieties are much more likely to develop rot than others.
In my garden this year, those varieties more prone to blossom end rot included San Marzano, Orange Banana and Better Boy.
Meanwhile, the rest of the crop was largely unaffected.
Amish Paste, Opalka, Blue Beauty, Stupice, Glacier, Black Cherry, Mortgage Lifter, Arkansas Traveler, Tigerella were among those without a problem.
A more scientific study was conducted by the University of Illinois. They found these varieties to have a low incidence of blossom end rot, with losses of less than 10% in severe years:
- Celebrity
- Fresh Pack
- Jet Star
- Manapal
- Mountain Pride
- Pik Red
- Sunny
- Winter
And these varieties had a loss of 15 to 30% or more in severe years:
- Big Boy
- Castle King
- Fantastic
- Independence
- Supersonic
- Surprise
- Whopper
- Wonder Boy
Does Epsom Salt Help Blossom End Rot?
Although commonly recommended as a “cure-all” for tomato plant, Epsom salt is not a good choice for stopping blossom end rot. It might even make the problem worse.
Epsom salt is magnesium sulfate. It contains no calcium. Magnesium and calcium ions vie for the same spots in the soil and plants, so extra magnesium may make exacerbate a calcium deficiency. It’s better to use the options above to make calcium more available.
Note – a little extra magnesium at blossom time can help with fruit set. Just don’t go overboard.
Can overwatering cause blossom end rot?
You betcha. Either too much water or not enough water (or rapid swings between the two conditions) can trigger BER. Use the methods listed above to help maintain even soil moisture.
I’d love to hear your experience with which varieties are more or less prone to be affected by blossom end rot in your area. If I missed any tips that work for you, or if you have any questions, please share those, too.
More Tomato Growing Tips
You may also enjoy:
- Grow Tomatoes from Seed – Save Money, Get More Varieties
- 4 Reasons your Tomatoes Aren’t Ripening
- 5+ Terrific Tomato Trellis Ideas
Originally published in 2016, last updated in 2019.
What is baking soda for?
What use of baking soda are you referring to?
Dealing with Blossom End Rot in Nevada. Not sure why. Moisture is an issue, but I can’t add less!! Gardening feels almost impossible here since I go camping nearly every weekend in the summer, and the lack of water over the weekend makes the tomatoes look like they got hit by a train. I have tried everything from deep mulch and deep watering before I leave (enough to leave a puddle). I water aggressively every day or the tomatoes wilt by 9 a.m. and the leaves dry up.
Nitrogen should not be an issue since I have just used a little compost based soil amendment.
Are you growing in a container or directly in the ground? Have you added plenty of calcium to the soil?
Have you tried a drip watering system? You can set up a simple system for each plant by inverting a large jug near the plant (or multiple jags, if needed) with the bottom cut off. Fill the jug as needed, and let it slowly feed into the soil. Depending on the situation, you might leave the lid on the jug and punch a few holes in it for a slow feed, or take the lid off if it has a narrow opening, like a 2 liter soda bottle.
Gardner Scott
8:21 Coconut Coir contains a very high level of potassium – which inhibits the uptake of calcium by most plants.
There were a few other studies on Coir vs. Peat moss. I grow in containers (my soil is rock hard in Arizona) I had bottom rot big time on my tomatoes when I used soil with Coconut Coir (although the plant looked nice)- last year I changed to no manure / no coir – planted in soil with peat moss – and I have had NO bottom rot for two years now.
That is interesting. Thank you. I had not seen this information before.
Gardening is therapy for me. Its just enjoyable. I never did much research until recently on the internet. Even though I find the information helpful some of it is just too scientific for me. It takes the pleasure of gardening and makes it a chore. So I’m going to take Craig’s advice and try DG tabs before buying expensive fertilizer and other treatments. Let you know if it cures the black rot here in SC!
To prevent Blossom End Rot all you need to do is add 3-4 cheap Dollar General antacid tablets, (750-1000mg), to the tomato hole when you plant. Also, add 3 more tablets as soon as small tomatoes are noticed! (Just poke a hole with your finger near the stalk, place tablet and cover hole). A professor at Clemson University told me this process wouldn’t work – “tomatoes require different kind of calcium”. He was full of “manure”…….I’ve been doing this for 10+ years…..NO Blossom End Rot!!! (Prior to using the antacid tablets, had BER on almost all my tomatoes, (all heirloom, ole-timey types). Oyster shells, egg shells, calcium spray, etc. DID NOT WORK. Cheap “rolaids” is the BEST WAY TO PREVENT BLOSSOM END ROT!!!
I have Roma’s bought from Lowe’s. I used a 10-10-10. Weeks before planting. ( I used raised beds due to heavy clay soil). At planting time I put epsom salt( tablespoonish). Crushed eggshells , Gypsum. And bone meal. And lightly incorporated a 4-4-4 fert. Getting blossom rot. Mainly on First to turn red.. toss. On utube saw guyI used a powdered milk and small amount of soil acidifier or white vinegar. My main problem is my house water test at 8.5., soil is generally 7.5 to 7. Tested rain water from collection barrels. It tested at 8 ph. I know calicum needs a co- binder for plant uptake. Side not tried beets they poofed I know they like boron. Used dog hair but… back to point. I think my water it way to height in ph at 8.5 sorry about mess of a letter. Tired.
It sounds like you should have plenty of calcium in the soil from the various amendments, so getting it to the plants does seem to be the bottleneck.
You mention a lot of different things, but what about plain compost and mycorrhizal fungi? Healthy compost normally contains a lot of bacteria and other microbes, that help to break down minerals in the soil to make them more available.
Mycorrhizal fungi are fungi that form symbiotic relationships with plants. They spread through the soil and break down nutrients to make them accessible to the plant, and in return, the plant shares carbohydrates to the fungi. They should naturally show up on their own over time, but tilling the soil disturbs their growth, so many gardens are lacking. You can buy the spores in granular form to jump start the population. Amazon stocks small containers that aren’t too pricey if you want to give it a try – Root Naturally Endo Mycorrhizae – 4 Oz.
Mulching the soil surface with organic material will also help maintain uniform soil moisture, and add organic material to the soil as it decomposes. Fall leaves will also help to gently acidify the soil.
All very interesting – and thank you, but I grow in a green house with growbags. I therefore ask is there anything specific to this type of growing have lost 1 plant of nine to BER
I haven’t had a lot of luck with grow bags. It’s tough to keep them evenly watered. My mom would take the entire bag and soak it in a basin every few days to wet it evenly, but that’s tough with large plants.
I’ve had mixed results. The one year I grew Brandywines (multiple plants) they were virtually a complete writeoff to BER. The Supremo tomatoes ( a paste type) are really prolific, but I typically lose 10 – 20% to BER. I’ve found that in my case the first set of tomatoes on a plant seem to be more prone, with those coming later less so. I’ve read in a couple of places that if the plant grows too fast it can’t take up enough calcium sometimes, and BER results. I use Earthboxes, and try to get the soil and lime in the box at least a few weeks before planting. I’ve tried epsom salts and calcium nitrate in the past and neither seemed to make a huge difference. I also went back to using pulverised eggshells directly in the hole 2-3 Tbsp- (I’ve got a LOT of crushed eggshell) this year and so far only have seen a couple tomatoes with BER. They’re not ripening, but at least they’re not rotting (yet).
If it’s driving you completely crazy try growing cherry tomatoes. Never had one on our Nectar tomatoes yet, or on the Maglia Rosa tomatoes I used to grow.
Thanks for sharing your experience. I’ve never had blossom end rot on cherry tomatoes, either.
I’ve noticed that my small, green tomatoes often have the dead blossom still stuck to their bottoms. On the off-chance that that dead blossom is “seeding” the rot on the tomato, I’ve begun wiping the dead petals off of the baby tomatoes. Not disputing the well researched calcium theory here. Just tending to my plants.
Healthy fruits should be unaffected by any lingering bits of blossom. If there’s a fungal issue, then clearing off blossom residue may help.