Blossom End Rot in Tomatoes: Causes, Control & Prevention Tips

Blossom End Rot in Tomatoes: Causes, Control & Prevention Tips

Blossom end rot is a common condition in tomatoes that can lead to a huge loss of tomato yield to gardeners. It is often mistaken for a tomato disease that needs some treatment. However, you might be surprised to find out that is not a disease but just a physiological defect that needs to be controlled without any fungicide of bactericide.

What is Blossom End Rot in Tomatoes?

The blossom end refers to the spot at the bottom end of a fruit to which the blossom once was attached. Blossom-end rot is a defect (physiological disorder) whereby the tissue of the blossom end of the affected fruit breaks down. This problem is quite common in tomatoes though it also affects other plants.

Blossom end rot on green tomatoes
Brown water-soaked area around the blossom end of tomatoes

In tomatoes, blossom end rot starts as a small water-soaked area around the blossom end at bottom of the tomato fruit and gradually widens. Eventually, the affected area becomes leathery, sunken, and turns dark brown or black as the tissue breaks down. These unique characteristics distinguish the defect from other brown or black spots on tomatoes.

These are the typical signs of blossom end rot in tomatoes. However, sometimes an internal black rot may develop inside the fruit with little or no external sign. In such cases, the defect causes underdeveloped internal tissue. Hence, the tomatoes will weigh less than usual because they are partially hollow.

Blossom end rot sunken bottom area
The typical signs of blossom end rot in tomatoes

In many cases, the now weak and susceptible tomato may be attacked by fungi or bacteria. This usually makes the affected area dark and fuzzy. This might cause the affected area or even the entire tomato to completely rot.

Blossom end rot sunken bottom
When attacked by fungi or bacteria, the affected area may become dark and fuzzy.

Blossom end rot usually starts to affect the fruits when they are about half full size grown and still green. However, it can still set in when they are smaller or bigger. The defect then continues to develop as the fruit grows bigger, though unhealthy.

The extent to which the tomato is affected may vary from one case to another. If the defect is not adverse, the upper region of the tomato may survive to maturity and get ripe. You may not be able to tell to what degree the tomato is affected until you cut it to reveal the internal parts.

What Causes Blossom End Rot in Tomatoes

Blossom-end-rot a very common condition in tomatoes that is caused by a calcium deficiency. This especially occurs in actively growing parts of the plant such as developing tomatoes. It is the insufficiency of calcium in the tomato fruit that causes the tissue at the bottom of the tomato fruit to breakdown.

Blossom end rot on green young fruits
Blossom end rote especially attack young developing tomatoes

As a result, the bottom of the tomato typically appears as an ugly decay or sunken black spot. There are two main reasons why tomatoes may lack sufficient calcium: inadequate calcium in the soil or the inability of the plant to take up calcium from the soil.

Inadequate Calcium in the Soil

In this case, there is insufficient calcium in the soil that the plant can take up and utilize. However, although this can happen, it is a very rare occurrence since soil almost always has enough calcium. The rare case often occurs when the soil has been reused several times, especially for tomatoes that are planted in baskets or pots.

Inability to Take up Calcium from the Soil

In this case, there is sufficient calcium in the soil but the plant is unable to take it up and utilize it. There are many reasons why the plant may be unable to take up calcium from the soil as outline below.

1. Inadequate Soil Moisture

Lack of sufficient soil moisture may occur due to prolonged heatwaves, drought, or failure to water the plants. In hot climates, it might be tricky to keep to maintain enough moisture in pots with big tomato plants during summer.

Water in the soil is the medium through which plants take up nutrients from the soil. This means that insufficient water in the soil will hinder the tomato plants from taking up calcium as well as other nutrients from the soil.

As a result, the tomatoes are likely to develop blossom end rot, especially if it happens just before or during the time they begin to set fruit. This is because the water needs of the tomatoes increase as they begin to set fruit.

2. Fluctuating Soil Moisture 

Fluctuating moisture in the soil because of irregular watering or any other reason will certainly stress the plant, especially its roots. This hinders the proper uptake of nutrients by the plant.

3. Too Much Water in Soil

Cases of too much water in the soil may arise from overwatering or waterlogged soils. Too much water in the soil will stress or damage the root of the plant. This will interfere with the ability of the plant to take up nutrients.

4. Excess Nitrogen in Soil

Excess nitrogen usually arises from using fertilizers with relatively too much nitrogen component. Too much nitrogen in the soil causes an imbalance of calcium and other soil nutrients. This leads to the inadequate uptake of calcium and other nutrients by the plant.

5. Use of Too Much Fertilizer

Using too much fertilizer causes the plant to grow too fast. The rate at which the plant takes up calcium can’t match the plant’s need due to the fast growth. This leads to a relative inadequacy of calcium in the plant.

6. Damaged Roots of the Plant

Root damage can also lead to decreased moisture intake. Cultivating too close to plants or burning them with fertilizer can reduce nutrient and water uptake through the roots.

7. Overcrowded Plant Roots

Overcrowded plant roots arise from close spacing, especially when the tomatoes are planted in pots or containers. It interferes with proper nutrient uptake by the plant.

8. Too Low Soil pH Level

Too low soil pH level ties up the calcium present in the soil chemistry. This hinders the plant from taking up enough calcium, much as it may be sufficient in the soil.

9. Excess Salts in the Soil

Excess salts in the soil change the soil chemistry, which leads to a nutrient imbalance in the soil. This interferes with the plant’s nutrient uptake.

How to Control and Prevent Blossom End Rot in Tomatoes

You can stop and prevent blossom rot in tomatoes by solving the potential or underlying causes of the problem. Add calcium if insufficient or deal with the factors that stop the uptake of calcium from the soil.

Add Calcium to the Soil if Inadequate

You may need to add calcium to the soil in case tests show that it is insufficient.  A good source of calcium such as gypsum.  You can also choose to add substances such as bone meal, oyster shell, or gypsum to the soil at planting time to minimize the chances of calcium deficiency in the soil.

Another way of maintaining calcium is using a fertilizer that contains calcium at planting time. Avoid ammonium fertilizers as they tie calcium in the soil.

Adding crumbled eggshells to your garden or garden compost from time to time will help maintain the calcium levels. However, plants will be able to pick the calcium only after the eggshells start to decompose.

Lime is usually used to correct pH levels but it also contains calcium. Therefore, if the soil also has a lower pH level, you can add lime to the soil instead of pure calcium sources. However, you only add lime after carrying out pH soil tests to determine the amount of lime required to correct the pH level. Never use lime as a way of adding calcium to the soil when the pH level is fine.

Apply Calcium Foliar Spray.

Foliar applications of a 5% dilute liquid calcium or kelp can be used as a faster way to correct calcium deficiency. For best results, combine the liquid calcium with a natural surfactant to increase the adhesion of the spray. You can also use Tomato Rot Stop.

However, the foliar spray is usually quick but temporary when the tomatoes start to blossom with a calcium deficiency problem. You will still need to fix the underlying problem to get a lasting solution.

Alleviate Factors that Hinder Calcium Uptake

1. Maintain Adequate Soil Moisture

Ensure your tomatoes get enough water, especially just before or while they are fruiting.  When the weather is extremely hot and dry, water thoroughly to moisten the soil to a depth of at least 6 inches daily or as it may be appropriate. You may use watering cones (Aqua Cones) to get water down into the root zone.

You can use a drip system with a timer or improvise a dripping irrigation system. Fill plastic bags or containers with water. Use a pin to make calculated tiny holes on the bottom and set them around the plant.

2. Maintain Consistent Soil Moisture

Water your tomatoes on a consistent periodic schedule. Use drip irrigation to let your tomatoes get water without failure even when you are away. In case of weather changes, counter them with calculated watering so that your tomatoes do not face water moisture fluctuation.

3. Apply Mulch to Retain Moisture

Apply 2-4 inches of mulch to conserve and maintain even soil moisture. Mulch retains moisture by preventing the sun from heating the soil directly during hot, dry days. Go for organic mulch as it will also improve the soil content over time. You can use Shredded newspapers, wood chips, straw, compost, or grass.

4. Prevent Too Much Water

Avoid overwatering your tomatoes, especially when they are grown in pots of baskets. Dig trenches to drain the soil for water-logged gardens or to keep running water away from the tomatoes.

5. Use Fertilizers with less Nitrogen

Avoid using high nitrogen fertilizers that accelerate vegetative growth and reduce the uptake of calcium by plants. A large selection of balanced organic fertilizers is available at Planet Natural.

6. Avoid Using Too Much Fertilizer

One of the reasons you may want to use excess fertilizer is to get faster results. But, as you now know, this may not end well. Just use the recommended amounts and give your tomatoes time to grow to avoid disappointment.

7. Prevent Root Damage

Avoid deep cultivation around the plants as much as possible after fruit set, especially in dry weather. This may damage, interfere or expose the roots to dry weather. Scraping the soil lightly with a hoe is usually sufficient to control weeds in the home garden.

8. Properly Space your Tomatoes

Space your tomatoes well, especially those are planted in pots or containers, to avoid overcrowded roots.

9. Maintain Proper Soil pH Level

Maintain a soil pH of 6.5 to 7.5 so that it can release calcium for the tomatoes. Carry out tests to determine the pH of the soil, with the help of an expert if you can’t do it yourself. In case the soil pH is lower than required, you will need to add a certain amount of lime. Use the test results to determine the amount of lime to be added.

10. Grow Less Susceptible Varieties

Some varieties of tomato may be more prone to blossom-end rot than others. Keeping garden records may help you choose the least susceptible varieties for your garden.

11. Let the Soil Warm up Before Planting

In cold seasons, allow the soil to warm up to about 70 degrees F. (21° C) before planting new tomatoes.

Can Blossom End Rot Spread to Other Tomatoes?

Since blossom end rot is not a disease, it will not spread from plant to plant. The other fruits may be affected independently if they also experience a lack of adequate calcium. You might even find that the defect affects only certain parts of your garden where there is inadequate calcium.

Hence, it would be useless to use herbicides or bactericides once you have established that your tomatoes are affected by blossom end rot. Simply ensure the fruits get enough calcium and you will not have any other new cases in your garden.

Can You Use the Section That Is Not Affected?

Yes. In some cases, the blossom end rot affects only a very small and shallow section of the tomato. There will be no harm using it so long as you check that the tomato is not rotten. If not rotten, carefully cut off the affected region and use the remaining healthy one.

Blossom end rot on ripe tomatoes
You can use parts of the tomatoes if it is not so much affected

However, tomatoes with such defects may not be suitable for commercial purposes. But you can use them at home or share them with your relatives and neighbors. This would help save the tomatoes rather than throwing them away.

Which Other Plants Does Blossom End Rot Affect?

Although blossom end rot is commonly known to affect tomatoes, it can also affect other plants. Some of these other plants it is known to affect include Zucchini, squash, pepper, cucumber, melon, and eggplants. The causes and solutions to the problem in these plants are similar to those in tomatoes.

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