Blossom-End Rot

How to Identify and Control Blossom-End Rot

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Blossom-End Rot

Blossom-end rot on tomato plant

Catherine Boeckmann

Here are tips on how to identify, control, and prevent blossom-end rot on your tomatoes and garden plants.

What is Blossom-End Rot?

Why are your tomatoes rotting on the bottom? Unfortunately, they probably have blossom-end rot. It is a common problem on tomatoes, eggplants, and squash caused by a low concentration of calcium in the fruit. (Calcium is needed for normal cell growth.) Blossom-end rot usually occurs when there are wide fluctuations of moisture, which reduces uptake and movement of calcium into the plant. When the demand for calcium exceeds the supply, the tissues break down.

Calcium deficiency during fruit formation can also be caused by too much nitrogen fertilizer, high salt levels in the soil, or damage to plant roots during cultivation. Be aware of these causes when caring for tomatoes in order to prevent blossom-end rot.

Some blossom-end rot is more or less normal in the first tomatoes of the season, since the plants are usually under stress during the initial fruit set. If the damaged portion is small, you can trim it off and enjoy the rest of the tomato. Hopefully the problem will ease, because after all, no one wants rotten tomatoes!

Identification

How to Identify Blossom-End Rot Damage

Usually blossom-end rot occurs when the fruit is green or ripening. It starts with a small, depressed, water-soaked area on the blossom end of the fruit. As the spot enlarges, it becomes sunken and turns black or dark leathery brown in color.

blossom-end-rot-identify.jpg

Photo Credit: North Carolina State University. Blossom-end rot appears as brown, sunken spots on your tomato.

Control and Prevention

How to Control Blossom-End Rot

  • Remove the affected fruit. There is not much that can be done. If the affected fruit is pinched off, the plant might blossom again and set normal fruit.
  • Apply a liquid calcium fertilizer after removing the affected fruit.

Prevent Blossom-End Rot

  • The key is soil preparation. Maintain a soil pH around 6.5. Lime the soil with calcium and increase the ratio of calcium ions to other competitive ions in the soil. Add crushed eggshells, gypsum, or bone meal to the transplant hole to fortify calcium intake. 
  • Maintain a more uniform moisture supply. Use mulches and/or irrigation to avoid drought stress. If it’s rainy, ensure plants have good drainage and soil dries out (but do not cease to water). Overall, plants need about once inch of moisture per week.
  • Avoid cultivating, or hoeing, near the roots of tomato plants. 
  • For fertilizer, use nitrate nitrogen instead of ammoniacal nitrogen (as the latter increases blossom-end rot).
  • Avoid over-fertilizing during early fruiting when blossom-end rot is more likely to occur.
  • Staking the plants when they’re young can also be helpful. See our video on properly staking tomatoes.

Share your advice, questions, and comments on blossom-end rot below.

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Blossom Rot / Calcium

When planting my tomatoes, I always throw a handful of crushed oyster shells in the ground with a light dirt covering and then spread them out around the stem to stop any slugs from stopping by. The calcium helps the plants and the slugs won't crawl across the sharp bits of shell.

Add powdered milk

Add powdered milk

I am fairly new to gardening, only 3 years of ground gardening and 1 year of straw bale gardening. In the book I read about straw bale gardening, "Straw Bale Gardens" by Joel Karsten, Mr. Karsten mentioned adding powdered milk (high in calcium) to the hole before planting the tomato plant. I did this and did not have any issue with bottom rot. I had a wonderful harvest of healthy tomatoes, except when the slugs starting coming. I took care of the slugs with Mr. Karsten's suggestion of putting a shallow container with some beer in it and sinking it in to the bale a little so it is easy for the slugs to crawl in but not crawl out. The slugs preferred the beer over my tomatoes, which made happy. I will definitely be planting in straw bales again next year!

hi... new to gardening this

hi... new to gardening this past year. we did pretty good until what people are calling 'late blight'. i was told once you have 'it', it stays in the soil. ???sounds like from reading this i can ammend the soil next year and will be fine??
please advise... and thank you :)

Hi Kriss, Late blight is very

Hi Kriss,
Late blight is very hard to get rid of. Please read our blog about late blight at
www.almanac.com/blog/gardening...

I have been told that crushed

I have been told that crushed tums is a good source of calcium for the garden. I have not tried it yet but plan to next year.

I keep on hearing about

I keep on hearing about blossom end rot over the years and usually end up with some of my plants. I keep getting told to increase the calcium level for the plants, but I can never find out where to get the calcium from. I have been told to mix crushed eggshells, but I live on my own, so consequently don't get many. I've asked friends, but they are all in the same situation.

If you have a calcium

If you have a calcium deficiency in your soil, it all starts with soil preparation next year. Start out by adding lime into the to 12 inches of the soil.
To know how much lime to add, it would be best if you knew your soil pH. You want a pH of 6.5 to 6.8 to free up calcium. If you do a soil test, the results will tell you the amount of lime to add. Usually, your county cooperative extension will give you a free soil test.
Adding crumbled egg shells to your compost or burying them in the garden is also a good idea over time.
Also, avoid over-fertilizing, especially with nitrogen which ties up the calcium in the soil.
It also helps to use mulch to keep the soil moisture even.
Keep the soil moist and water evenly. Using a soaker hose at the plant's base is best.
Some readers use calcium sprays as a short-term fix. You'll want to ask your garden center about a spray.

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