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You waited all year for summer to come so you could plant tomatoes. Then, you waited all summer for your tomatoes to start coming in. And now that they finally have, something's wrong: There are yucky dark patches on the bottom of your tomatoes. Womp-womp.
This ailment, known as blossom end rot, is a pretty common disorder affecting tomato plants—but did you do something wrong to cause this? Can blossom end rot be reversed? And is there a way to prevent it?
To learn more about blossom end rot on tomatoes, Parade consulted with two gardening experts: Siobhan Shaw, Co-Founder ofthe nonprofit Growing To Give and Founder and Editor of The Gardening Network, and Sarah Carter, Vice President, Goizueta Gardens and Living Collections at Atlanta History Center.
According to Shaw, "blossom end rot is one of the most disappointing things a new tomato grower can find."
But despite this, both experts concur that if your tomatoes are currently suffering from blossom end rot, there's still hope of rescuing your garden.
"The good news is that [blossom end rot] is not a contagious disease and can be prevented," Carter tells Parade.
"Future tomatoes on the plant are often perfectly healthy once growing conditions improve," adds Shaw.
Keep reading for everything you need to know!
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What Is Blossom End Rot on Tomatoes?
"Blossom end rot is a common physiological disorder that affects the fruits of tomato plants," Carter explains to Parade.
"It is called 'blossom end' because it develops where the flower was before dropping off when the fertilized ovary formed into a fruit at the bottom of the tomato," she continues. "The 'rot' refers to the circular, dark, sunken, leathery patch caused by the disorder, which can develop from a small spot to halfway up the tomato."
Per Shaw, the first sign of blossom end rot on a tomato is a "dark, leathery spot on the blossom end or bottom of the fruit. It usually starts as a small water-soaked area that grows into a sunken brown or black patch."
Why Is Blossom End Rot on Tomatoes Bad?
"Blossom end rot ruins the quality of the fruit and makes it disappointing to harvest after weeks of waiting. Once that dark spot develops, the damaged tissue won’t heal or return to normal," explains Shaw.
"Tomatoes are disfigured when affected by blossom end rot, with the affected parts becoming unappealing and inedible," adds Carter. "The individual fruits cannot recover."
In some cases, you can still use part of a tomato that has blossom end rot. However, "in severe cases may also allow secondary rot to develop, making the tomato unusable. It’s a hair-pulling setback, especially for first-time gardeners," says Shaw. (More on all that below.)
What Causes Blossom End Rot on Tomatoes?
Blossom end rot on tomatoes "all comes down to calcium," per Shaw. Specifically, a lack of calcium during the tomato's development causes the plant to develop blossom end rot.
"Blossom end rot happens when developing tomatoes don’t receive enough calcium as they’re growing," Shaw explains.
But what causes the low calcium in the first place? According to Carter, inconsistent watering is the No. 1 cause of low calcium.
"Calcium travels entirely in water, from uptake by the roots, pulled through the stems by the rapidly growing leafy parts of the plants, and lastly, to the developing fruits," she explains. "Fruits are already at the branch tips and end of the line, so a lack of water can mean no calcium arrives to the far end of the fruits."
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Carter notes that blossom end rot is most commonly observed early in the tomato growing season, since the roots are not yet fully developed at this point. "Any lack of water at this critical point can cause blossom end rot, even if there is plenty of calcium in the soil (and there usually is plenty of calcium)," she says.
"Sometimes the soil is actually low in calcium, but more often the calcium is there and the plant can’t absorb it because of inconsistent watering, drought stress, or damaged roots," adds Shaw.
How to Fix Blossom End Rot on Tomatoes
Blossom end rot cannot be reversed—but you may still be able to salvage affected tomatoes as well as your tomato plants.
"Unfortunately, once a tomato develops blossom end rot, there’s no way to repair that fruit. The damaged area won’t heal," says Shaw. "The best approach is to remove the affected fruit if it’s badly damaged, or cut away the rotten portion if the rest is still usable."
She advises using the sound parts of the tomato to make things like salsa and marinara sauce—as long as no secondary rot has developed. Secondary rot manifests as soft gray mold, per the University of New Hampshire.
Once you've removed all of the damaged tomatoes, your plant should be able to grow more healthy tomatoes—as long as you remedy the calcium issue.
"Focus on correcting the underlying problem by maintaining even soil moisture and making sure the soil has adequate calcium." says Shaw. "Future tomatoes on the plant are often perfectly healthy once growing conditions improve."
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"Once you have noticed the problem, your best bet is to ensure consistent watering of the tomato plants," adds Carter, who recommends evenly watering 1 to 2 inches per week.
Additionally, she suggests putting a layer of mulch on the soil, as it will help reduce weeds as well as keep soil temperature and moisture more consistent.
How to Prevent Blossom End Rot on New Tomato Plants
Before starting a tomato garden, both experts recommend testing your soil's calcium levels. In fact, Carter notes that your county's extension office may offer this service to residents.
If your soil turns out to have a calcium deficiency, Carter suggests treating it with agricultural lime. She also says to avoid over-fertilizing or fertilizing when soil is dry, and she notes that you should always" plant in a sunny location with fertile, well-drained soil high in organic matter."
Once you've planted your tomatoes, shift your energy to proper watering.
"The most important thing is to build healthy soil before planting and keep watering consistent throughout the growing season," adds Shaw. "Once the soil and watering are in balance, future tomatoes are much less likely to develop blossom end rot."
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Sources:
- Siobhan Shaw, Co-Founder ofthe nonprofit Growing To Give and Founder and Editor of The Gardening Network
- Sarah Carter, Vice President, Goizueta Gardens and Living Collections at Atlanta History Center
- Growing Vegetables: Managing Blossom End-Rot. University of New Hampshire.
