Blossom-End Rot in the Home Garden

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It’s always a great feeling to be able to pick that first ripe tomato off the vine in summer. You’ve put lots of time and effort into creating the perfect garden for tomatoes to grow. That’s why it can be majorly discouraging when you notice the bottom ends of the tomatoes (and possibly other plants) are rotting! Why is that?

When you see tomatoes, peppers, or even watermelons that have decaying bottoms, the first thing to come to most people’s mind is some sort of disease. In fact, blossom-end rot usually comes from an imbalance of plant-available calcium in the soil, making it a physiological disorder of the plant. Blossom-end rot most commonly affects tomatoes, but it isn’t uncommon to see peppers, squash, cucumbers, watermelon, and other cucurbits affected.

How can I determine that it is blossom-end rot and not something else causing the disorder?

Blossom-end rot always occurs on the blossom end of the fruit, hence the name. If the disorder is elsewhere on the fruit this could be indicative of another disease-causing agent. Sometimes sunscald is mistaken for blossom-end rot. With sunscald, the discoloration will be more yellowish to white in color and can occur anywhere on the fruit. Again, think about where exactly the disorder is occurring.

green tomato on vine with a decaying bottom

An unripe, green tomato suffers from blossom-end rot caused by a calcium deficiency in the soil.

What should I do?

If you notice that a plant has some fruits that are affected by blossom-end rot, go ahead and pick off these fruits and dispose of them. Picking the bad fruit will cause it to be less likely to happen to new and developing fruit. Most of the time, only a small portion of the fruits will be affected, so this really isn’t a big loss in a home garden. Seeing symptoms of blossom-end rot lets you know your soil is calcium deficient, so pull out your most recent soil test or consider sending off samples. It’s a free service!

When looking at the soil test, check whether any lime was recommended for the garden. Lime is primarily used to raise the pH of the soil, but also contains calcium, usually in the form of calcium carbonate, which disassociates in the soil to become plant-available calcium. Lime takes a long time relative to fertilizer to take effect, so think about when you applied it. Was it during planting or many months prior?

If you applied lime according to the soil test only shortly before planting, then your soil is probably deficient in calcium due to low pH. The best remedy would be to lime your soil according to the soil test report in the fall or during the resting period for the soil in your garden. Doing so allows the lime to react in the soil and take effect before the next planting season.

If you did apply lime according to the soil test but are still experiencing calcium deficiencies, then you could have soil with naturally low levels of calcium. Pay attention to the pH on the soil test report. If it is within the 6.0-6.5 range, then no lime is needed. Adding additional lime will only continue to push pH higher, causing other issues. So, if pH is within the correct range but you’re still experiencing issues with calcium (blossom-end rot), then you may consider using gypsum. Gypsum is used to increase the levels of calcium without increasing the pH of the soil. Use gypsum at a rate of 1-2 pounds per 100 square feet in your garden. As with lime, gypsum needs time to take effect in the soil. It is best applied months in advance.