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No one likes to spend their precious time nurturing a tomato plant, only to have the dreaded blossom end rot show up on their fruits. This common malady on tomatoes can be prevented and potentially treated in established plants, so that all of your hard work and nurturing isn’t all for naught (or rot)!

What is blossom end rot?

Blossom end rot starts at the bottom of a tomato, right where the blossom used to be. It begins as a small black spot that continues to enlarge, causing the tomato tissue to rot and the fruit to become deformed.

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Blossom end rot is a common problem in garden tomatoes and is typically caused by a calcium imbalance within the plant. However, the problem can also be caused by over-watering or under-watering, or a combination of both. So, what’s a gardener to do to keep tomatoes growing strong and healthy?

Calcium-rich soil and consistent watering are essential for preventing blossom end rot in tomatoes, but there are also a few other things gardeners can do to prevent this particular problem.

Blossom End Rot Causes and Prevention

Inconsistent watering, as mentioned above is a common culprit. Too much or too little water hinders the plant from being able to uptake calcium from the soil. 

A calcium deficiency in the soil can also be caused by too much nitrogen or damaged plant roots. This is another reason why having your garden soil tested annually is always a good idea. (See my post here about building up garden soil, which includes details on how to get your soil tested locally for free!)

How to add calcium to your garden

If you’ve been watering consistently and determined that a calcium deficiency is the reason for your blossom end rot, then consider this homemade prevention. Incorporate one-half cup of gypsum and one-half cup of Epsom salt into the soil at planting time to help prevent blossom end rot.

Some other gardeners I’ve talked to over the years also add egg shells to the area where they plan to plant tomatoes. These do take a while to break down, so begin preparing the area in the winter (if possible). Another DIY calcium tip from a fellow Master Gardener is to add a Tums to the planting hole. This gives a quick shot of calcium to the plant! Choose any flavor you want; I don’t think the plant is too picky.

Stop the rot from spreading

Tomatoes with blossom end rot will not recover, remove them from the plant and discard them. In some instances, just the first few tomatoes will be afflicted with blossom end rot. If you notice that all your tomatoes have this issue, then proceed with a course of treatment.

Unaffected green tomatoes will mature normally if the calcium deficiency is corrected.

The plant can be saved with an application of Epsom salt to the plant roots. Mix one-half cup of Epsom salt in a gallon of water and water plants as usual. Sprinkle Epsom salt around plant and work lightly into soil, being careful not to allow Epsom salts to touch plant stem. This will prevent future tomatoes from developing blossom end rot.

Apply mulch

Apply a 3-4 inch layer of organic mulch around tomato plants to help retain soil moisture. This will help with the watering issue that can lead to blossom end rot.

Applying mulch will also prevent weed growth and keep certain types of pests off of plants. Use a good quality natural mulch and avoid the dyed wood chips that can actually prevent water from getting to the roots of the plant. (See this excellent article on the best types of mulches to use in the garden.)

Other blossom end rot preventive measures

Another suggestion is to reduce fertilizer applications during early fruiting, when blossom-end rot is more likely to occur. Nitrogen content is high in most fertilizers and nitrogen increases the chances of tomato plants developing blossom end rot. If you want to use a fertilizer at this point, be sure to choose one that is specific to fruiting plants, such as Big Bloom by Fox Farm, which has no nitrogen. This will still encourage your plant to grow, but won’t give excess nitrogen that your tomato plant doesn’t need.

Also, damaged roots can hinder the ability of the plant to uptake calcium from the soil. Be careful at planting time not to damage roots and during cultivation be careful not to dig too close to plant roots. Check out my article all about how to plant tomatoes to get tips on what to do.

So here’s to a fabulous tomato harvest this year! Don’t let a rotted tomato bottom or two discourage you. Instead, check your watering practices, avoid high nitrogen fertilizers, and add calcium to your soil if needed.