Tomato Diseases: How To Fight Blossom-End Rot

by Matt Gibson

About Blossom-End Rot

When the growing season in your region starts out with lots of rainy days and then shifts to dry conditions as the fruit is setting, watch out for blossom-end rot (BER). When your tomatoes are about half of their mature size, damage may start to occur, appearing as large water-soaked areas that quickly enlarge and turn dark brown and leathery. These areas are actually rotting, so fruit must be picked and discarded.

The water-soaked spots occur at the blossom end of the fruit (or the bottom side), hence the name of the condition. Blossom-end rot is not actually a disease, but a physiological disorder that is caused by a calcium imbalance in plants. Blossom-end rot is common in tomatoes, as well as peppers, eggplant, melons, and squash.

Causes And Symptoms of Blossom-End Rot

In soils with calcium deficiency, blossom-end rot is a common issue. Low levels of calcium can be caused by depleted soils, poor drainage, and displacement due to transpiration most especially when your tomato plants are under stress. Low calcium levels in soil is not a common issue, and it’s not the only cause of blossom-end rot.

There are quite a few environmental factors that can lead to blossom-end rot issues as well, including:

• heavy rainfall or overwatering
• uneven watering (often caused by periods of drought)
• root damage from cultivation
• too high or too low soil pH levels
• cold soil
• soil that is high in salts
• fast climbing temperatures or extreme heat
• rapid plant growth due to an overabundance of nitrogen early in the plant’s life cycle

A lack of calcium uptake is still at the root of the problem. These common environmental conditions cause plants to be unable to absorb enough calcium at a fast enough pace to keep up with the growth of the plant, or cause the plants to have trouble processing the calcium that they do take up because of stress from environmental causes.

Blossom-end rot usually occurs when the fruit is green or ripening, starting with a small, water-soaked, sunken areas on the bottom of the fruit. The spot then enlarges, becomes more depressed (physically, not emotionally) or sunken, and begins to turn dark, leathery-brown or black in color.

When calcium levels are too low for healthy growth, plant tissue begins to break down, causing the rot. If spotted early enough, you can cut around the rotten part and salvage some of the tomato if desired. Eventually, the rot will cover the lower half of the developing tomato fruit which will become concave, or flat, destroying the entire tomato.

Control and Prevention of Blossom-End Rot

The only control method for blossom-end rot is to remove the entire fruit. Once the rot has set in, there is not much you can do for the particular fruit that has been affected, but if you remove it from the plant, there is a chance that a healthy fruit might grow back in its place. Apply a liquid calcium fertilizer after removing the affected fruit to improve your chances of growing healthy tomatoes moving forward.

The best method of protection against blossom-end rot is prevention. The following prevention tips will help keep blossom-end rot out of your tomato beds:

• Avoid cultivating, chopping, or hoeing near the root system of your tomato plants to keep from damaging the roots.
• Make sure not to over-fertilize during early-fruiting, when BER is most likely to strike.
• Soil test and keep soil pH around 6.5 adding lime to increase the calcium ratio. Add gypsum, bone meal, or powdered milk to the transplant hole to increase calcium intake. You can also add crushed eggshells, but keep in mind that they take a long time to break down and fortify the soil with calcium and are more of a long-term fix to increasing calcium levels in the soil.
• Commercial calcium sprays can be applied directly to plants when blossoms first appear.
• Use organic mulch, as well as manual irrigation (as needed) to maintain a consistent water supply. If you get heavy rain in your area, make sure your tomato beds have good drainage and soil dries out between waterings but continue to water when needed. Ideally, provide around one inch of moisture per week,
• Use a nitrate nitrogen fertilizer instead of ammoniacal nitrogen. Ammoniacal nitrogen can actually cause BER flare-ups.
• Stake young tomato plants when needed

Common Questions and Answers About Blossom End Rot

Can blossom end rot be stopped?

With proper treatment, it is possible to stop blossom end rot and even reverse the progression of the disease. While individual tomatoes can’t be salvaged once they’re affected, the plant itself can be nurtured back to health. Just follow these steps to stop blossom end rot in its tracks so your plants can produce many more disease-free tomatoes.

First, all affected fruits should be discarded. Then give affected tomato plants a jolt of calcium by adding powdered milk to the water you use to hydrate them. (You’ll sometimes see eggshells recommended as way to give plants calcium, but it takes time for the shells to decompose and release their calcium. The calcium in powdered milk will be available to your tomato plants immediately when you use it to water them.) Gardeners also use 4-12-4 or 5-20-5 fertilizers, or any fertilizer low in nitrogen and high in superphosphates, to prevent blossom end rot.

Finally, you should ensure your plants are getting plenty of water on a set schedule, as inconsistent watering can be the culprit behind blossom end rot. Make sure to water tomato plants daily. If you live in a particularly warm area or are going through a hot spell, you may even need to increase your watering schedule to twice per day. Water to a depth of six inches. It can take a few weeks of consistent hydration to see results, so don’t be discouraged if healing isn’t immediately apparent.

Can overwatering cause blossom end rot?

Blossom end rot can occur due to either overwatering or underwatering, as the real problem is irregular watering. It’s most likely that tomato plants afflicted with blossom end rot went through a dry spell when they weren’t watered enough, then in an attempt to correct the problem, were overwatered next. Another scenario could be when the growing season starts out especially wet, then as the plants are setting fruit, the weather turns dry. Blossom end rot is most often caused by both inconsistent watering and a lack of calcium in the soil.

To treat blossom end rot, do not permit soil to completely dry out in between waterings. Tomato plants should be watered daily to a depth of six inches—and in particularly hot regions or times of year, they may need to be watered twice per day. Gardeners can also use a layer of mulch to help soil retain water and stay more consistently moist. (You can learn more about mulching in our Guide to Using Mulch the Right Way.

To address the lack of calcium in the soil, simply add some powdered milk to the water you use to hydrate your tomatoes. Powdered milk provides calcium immediately, while the eggshells that are often recommended take time to release the calcium they hold. You can also nourish your plants with fertilizer low in nitrogen and high in superphosphates, such as 4-12-4 or 5-20-5 blends.

Can you eat a tomato with blossom end rot?

Yes, you can cut away the rotted portion of your tomatoes and eat the rest. However, many people find that tomatoes affected with blossom end rot have a mealy texture and are less flavorful than healthy tomatoes. While you can eat them fresh, tomatoes that show signs of blossom end rot should not be preserved through canning or other methods.

Does blossom end rot affect the whole plant?

In short, no—blossom end rot affects the fruit only, not the entire plant. But it’s a little more complicated than that. The signs of blossom end rot are only apparent on the fruit of the plant, but blossom end rot can be due to issues with the root system. An underdeveloped root system may fail to draw the needed water and calcium from the soil, and the lack of those nutrients can result in blossom end rot. In other words, while the roots can contribute to blossom end rot, the disease’s impact is limited to the fruit of the plant where symptoms of the disease appear.

Does Epsom salt stop blossom end rot?

Adding Epsom salt to soil does not stop blossom end rot. On the contrary, it can contribute to causing blossom end rot in your plants. Blossom end rot is caused by inconsistent watering and lack of calcium, and Epsom salt doesn’t contain calcium. It does contain magnesium sulfate, and the magnesium it adds to the soil battles against calcium ions to be drawn into the plant’s root system.

Instead of Epsom salt, use powdered milk added to the water you give your plants to boost their calcium intake, and be sure they’re getting plenty of water on a consistent basis. When you’re having trouble with blossom end rot, don’t permit the soil to dry out between waterings. In hot regions or times of year, that may mean watering your plants twice a day instead of just once. Water to a depth of six inches each time. Adding a layer of mulch may also help keep moisture more consistently available in the soil. Another preventive measure against blossom end rot is fertilizer low in nitrogen and high in superphosphates, such as a 4-12-4 or 5-20-5 fertilizer.

How do you prevent blossom end rot?

You can prevent blossom end rot by ensuring a consistent watering schedule that meets the needs of your plants and providing plenty of calcium in the soil. Water your plants to a depth of six inches daily, and when weather is especially hot, you may need to water twice per day. Using a layer of mulch can help keep moisture in the soil, reducing the likelihood of it drying out in hot or dry weather.

If your region is cold at planting time, wait for soil to warm up a bit before planting your tomatoes. Cold soil can prevent your plants from taking in sufficient nutrients. Ensure that the pH level of your soil is around 6.5. (If you aren’t sure of your soil’s pH, read our article on how to test pH levels.)

You can make sure your soil has plenty of available calcium by adding powdered milk to the water you give your plants. Powdered milk will make calcium immediately available, as opposed to the eggshells you’ll sometimes see recommended, which need time to decompose before plants can access the nutrients they hold. Nourishing plants with a 4-12-4 or 5-20-5 fertilizer, or any blend low in nitrogen and high in superphosphates, also helps prevent blossom end rot.

How do you stop blossom end rot on tomatoes?

With proper treatment, you can stop the progression of blossom end rot. Although you won’t be able to recover fruits that are affected, you can heal the plants so they can produce more healthy tomatoes throughout the season. To stop blossom end rot on tomatoes, ensure your soil has plenty of calcium to offer, and water your plants consistently.

Adding powdered milk to the water you give your plants is the best way to boost available calcium in the soil. Some gardeners recommend eggshells, but it takes time for the eggshells to decompose and release calcium into the soil, unlike the immediate availability powdered milk supplies. Another supplement to fight blossom end rot is fertilizer that’s low in nitrogen and high in superphosphates, like a 4-12-4 or 5-20-5 blend.

Water your plants to a depth of six inches, and do not permit soil to dry out between waterings. In especially hot or dry climates or times of year, this may mean watering twice a day instead of once a day. A layer of mulch on top of the soil can help lock in moisture so it’s consistently available to your plants. It can take a few weeks of proper watering to kick blossom end rot to the curb, so don’t despair when recovery takes a little time.

How do you treat blossom end rot?

Treat blossom end rot by giving plants consistent access to water and by making calcium available in the soil. You can solve a lack of calcium by adding powdered milk to the water you give your plants. Powdered milk is more efficient than eggshells at providing your plants with calcium, as eggshells must decompose to release the nutrients within them into the soil. When it comes to watering, make sure you’re watering deeply and frequently enough. You can feed your plants with a 4-12-4 or 5-20-5 fertilizer, or any blend that’s low in nitrogen and high in superphosphates.

Water your plants to a depth of six inches, and don’t let soil dry out between waterings. If it’s particularly hot in your area or you’re going through a dry or hot spell, you may need to water plants twice a day instead of once daily. You can help lock moisture into the soil with a layer of mulch. It can take a few weeks for your plants to get rid of blossom end rot, so don’t give up if you don’t see the results of your adjustments right away.

How does blossom end rot spread?

Blossom end rot does not spread between plants in the garden because it isn’t a virus, fungus, bacteria, or the result of insect infestation. Blossom end rot strikes when plants don’t have access to enough calcium in the soil and when they’ve experienced inconsistent watering. An underdeveloped root system may prevent plants from taking in enough water and calcium even if it’s present in the soil for them as well.

Because blossom end rot isn’t contagious, you don’t need to remove and discard affected plants. If you provide them with calcium and plenty of consistently available moisture, in a few weeks they will begin producing healthy fruit again. That said, you should go ahead and remove any fruits that show signs of blossom end rot so your plants won’t devote energy and resources to them. While it’s safe to eat the portions of fruits that aren’t rotted, the texture and flavor will be subpar.

Should I remove tomatoes with blossom end rot?

Yes, you should remove tomatoes that show symptoms of blossom end rot. Though they aren’t contagious and the unaffected portion is safe to eat, the fruit will be mealy and lack flavor. Removing affected fruit also prevents your plants from devoting their energy to developing damaged produce, too, encouraging the creation of healthy new fruits instead.

What can get blossom end rot?

Plants that can get blossom end rot include apples, cucumbers, eggplants, melons, peppers, squashes, and tomatoes.

What can I use for blossom end rot?

Treating blossom end rot is a matter of providing sufficient calcium and consistent water for your plants. You can give plants a quick boost of calcium by adding powdered milk to the water you give them. Powdered milk is more efficient than eggshells, which must decompose before calcium is available. Water to a depth of six inches, and don’t permit the soil to dry completely between waterings. If it’s especially hot in your region or you’re going through a hot or dry spell, you may need to water plants twice a day instead of once. A layer of mulch on top of the soil can help keep water consistently available for the plants’ roots.

You can also plant your seeds a little later in the season if the weather is cold at planting time, as cold soil can prevent roots from taking in enough water and nutrients. Avoid cultivating the soil too near your existing plants so you don’t cut through their feeder roots. Positioning your plants where they’ll get some shade can also help when it’s dry, hot, or windy in your region. You can also nourish your plants with a fertilizer high in nitrogen and low in superphosphates, like a 4-12-4 or 5-20-5 blend.

What causes blossom end rot on tomato plants?

Blossom end rot occurs when plants aren’t getting enough calcium and haven’t had consistent moisture. It may happen when the weather was wet at the start of the season, then turned dry when plants began to set fruit. Any circumstances that cause underdeveloped roots can lead to blossom end rot, as the roots may not be able to take in sufficient water or nutrients.

What does blossom end rot look like on tomatoes?

Put simply, blossom end rot creates rotten-looking patches on the bottom of tomatoes or other affected fruit. At the base of fruit where the blossom used to be, blossom end rot creates water-soaked patches that start out brown or yellow, eventually turning black and leathery in texture. The discolored area can be quite large, covering up to half of the affected fruit.

Why does blossom end rot happen?

Blossom end rot happens when plants aren’t getting enough water on a consistent basis and when they aren’t taking in enough calcium. This can happen if calcium isn’t available in the soil or if roots are underdeveloped and unable to take in sufficient moisture and nutrients. Blossom end rot can also strike if plants get too much water at the beginning of the season followed by not enough water when they begin to set fruit.

Will TUMS help blossom end rot?

The amount of TUMS that would be required to provide sufficient calcium to help with blossom end rot makes this treatment ineffective. Another commonly recommended remedy for blossom end rot is eggshells, but it takes time for the shells to break down and release their calcium so it’s accessible for plants.

However, gardeners report success fighting blossom end rot when they add powdered milk to the water they give their plants. Many times, though, the problem behind blossom end rot isn’t only a lack of calcium but also inconsistent watering. To treat blossom end rot, plants need a few weeks of consistently available sufficient moisture to turn things around.

Water your plants to a depth of six inches, and don’t let the soil dry out completely between waterings. If it’s particularly hot or dry in your area, you may need to water twice a day instead of just once. Adding mulch or positioning plants where they’ll get some shade can also help keep moisture in the soil.

Want to learn more about how to fight tomato blossom-end rot?

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