Blossom End Rot On Watermelons

The watermelon plant belongs to the Cucurbitaceae family that produces flowers. It produces delicious fruits that are eaten worldwide and are full of nutrition. But it can be affected by various harmful diseases.

Blossom end rot is also one of them. This piece of content provides detailed information on Blossom End Rot on Watermelon. 


  • The appearance of the burned portion of the fruit of the watermelon plant. 
  • Formation of light brown spots that turn into lesions that darken and dry over time. Sunken leathery spots are also visible. 
  • Decaying of fruits at a fast rate. 

Although the disease is not contagious, the removal of infected plants is a must. 

Causes of Blossom End Rot On Watermelons

  • Water is taken into plants through their root system. It is utilized by plants and some of it evaporates. Water evaporates from the leaves of plants. This situation occurs when the sun warms up the plant surface. Water from leaves transpires and more water takes its place and thus the plant does not burn. The leaf surface is smooth, water movement from other parts to leaves is easy and quick.

On the contrary, fruits have harder skin. Thus, the movement of water is not fast as the pull of water is slow. 

Therefore, the bottom portion of the fruit deprives moisture and burns. It usually darkens or appears shriveled. Decaying also starts occurring eventually. More organisms like insects can attack easily. 

  • Imbalance in Ca levels is also a major cause of blossom rot in watermelon. Ca is immobile relatively. But due to heavy transpiration Ca be moved to leaves in high amounts making fruits deprived of them. 

Prevention of Blossom End Rot On Watermelons

Soil conditions

Proper soil conditions are so important to ensure healthy growth in plants. In case the soil fertility of your planting site is unfit, a variety of diseases and abnormalities are bound to occur. Infected plants are of no use and even distracts from a healthy crop. 

Therefore, getting your soil tested is highly recommended. It will aware you of things that your soil has more or what it lacks. Moreover, it is important to know the pH level of the soil. 

All you need to do is, take a small sample of soil and take it to the nearest lab for agricultural testing. It will provide you proper details about the nutrient level and pH level of the soil. 

This will make sure you provide only necessary nutrients and do not overdo it. 

In the case of watermelon, 6.5 on a pH scale is perfect for its growth. Anything above or below will lead to complications. 

Fall is a perfect time to test the soil before sowing watermelon seeds in the spring season.

Next, if the soil lacks in Ca, it leads to blossom end rot in watermelon. After checking soil 3 months before planting, add lime to the soil to overcome Ca deficiency. 

Get the soil tested every 3 years for proper growth. If soil is problematic then annual testing is suggested. 

Must Read: How To Do Watermelon Farming?


Keeping the soil moist at all times with proper and regular watering is a must to avoid this disease. 

The water content of soil changes and keeps fluctuating from dry to wet at times of watermelon blossoming is inadequate. This can lead to melon blossom end rot in watermelons. 

Irregular watering leads to uneven intake of Ca by watermelon plants. 

However, this disease can be caused even when there is a proper amount of Ca. if there is improper water at the time of fruit formation or blossom developing. 

To avoid disease, 1- 1.5 inch water level should be provided during fruiting periods. 

Nitrogen Content 

If nitrogen is present in limited amounts in soil, blossom end rot can occur possibly. 

The work of nitrogen is to increase the size of leaves in plants. If nitrogen is found in an improper amount, the size will be affected obviously. 

Due to this, more Ca is directed towards fruits. This leads to an imbalance in Ca amount and causes Blossom end rot. 

Watermelon rotting on Vine

Watermelons rotting on the vine are possibly visible in conditions like Blossom end rot, Belly Rot, Gummy Stem Blight, Bacterial Fruit Blotch, and Rind Necrosis. 


  • Watermelons should be planted in well-drained soil to ensure proper watering and moisture conditions. This ensures plants develop a deep and large root system to absorb healthy amounts of Ca from the soil. 
  • Mulch can also be used to retain moisture in the soil. It compresses weeds too. 2-4 inches of mulch is perfect for watermelon plants. It holds moisture in the soil by blocking evaporation. 

Watermelon Growing Problems

Growing watermelon is not a piece of cake. It comes with problems. There can be watermelon plant problems that affect fruiting and render plants useless. 

Few diseases and abnormalities are mentioned below-

  • Leaf Curling- leaves curl under and turn yellow. They get deformed and can be easily identified. Aphids are tiny, oval creatures that reside on the underside of leaves and lead to this abnormality. It releases a sticky substance known as Honeydew. It is advised to use insecticidal soap. 
  • Leave discoloration- leaves start turning yellow, pale green, or brown. Spider mites can be a possible reason behind this. Spraying water can help in getting rid of such insects. Infected leaf removal can be better as it protects the whole plant. 
  • Tunnels on leaves- Trails or tunnels are observed on leaves. It is caused by leaf miner larvae. Cultivate a garden to decrease this disease occurrence. Larvae get destroyed upon cultivation. 
  • Water-soaked blotches- leaves get infected and suffer from the appearance of water-soaked blotches. Angular leaf spots can appear which turn yellow or crisp. Pruning leaves infected by this disease can prove helpful. Do not wet foliage much as wetting leads to disease. 
  • Bitter Fruits- inadequate pollination can cause bitterness of fruit and misshapen fruits. Dry soil and high temperatures also lead to this condition. Poor soil fertility is disastrous. 


Blossom end rot is a harmful condition in plants that destroys fruit and makes them inedible. Infected fruits cannot be treated to turn them into healthy ones. But, prevention is better than cure.

Therefore, following the preventive measures mentioned above can assure you healthy and edible fruits of melon. 

Why Are Bottom of Tomatoes Turning Black: Blossom End Rot

If you are worried about why your tomatoes are rotting on the bottom then you have come to the right place. Let us discuss this issue of tomatoes turning black that many people are facing nowadays, and let us provide you the best solution to this problem.

The classic symptom of blossom-end rot is a water-soaked spot at the tomato fruit blossom ends. This relatively common issue with the garden is not a disease but rather a physiological condition induced within the plant by a calcium imbalance. It can occur in fruits such as pepper, squash, cucumber, and melon, and tomatoes.

When the growing season starts wet and then becomes dry and the fruit is set, then the ‘blossom-end’ rot is most common. Damage occurs first when fruits are around half their full size. The water-soaked areas enlarge and turn dark brown and leathery. Eventually, these areas may start to rot, so the fruit should be picked and discarded.

My tomatoes have black bottoms but why?

Several factors can restrict a plant’s ability to absorb enough calcium for correct development. These include soil moisture variations (too wet, dry), soil nitrogen abundance, cultivational damage to the root, soil pH too high, soil pH too thin, salt cold, and high soil.

How to prevent and control this problem?
  • Keep constant soil humidity levels throughout the growing season. Water once or twice a week, when the weather is dry, to damp the field to a depth of 6 inches or less.
  • Prevent Tomato Rot Avoid calcium deficiency.
  • Enable soil to warm before seeding in cold climates; cold soils restrict the intake of nutrients.
  • Keep soil pH at or close to 6.5.
  • We are using nitrogen-free and phosphorous-high fertilisers like our GSC Organic Tomato Fertilizer.
  • To get water down to the root field, use watering cones (Aqua Cones).
  • To mitigate evaporation and to maintain consistent soil moisture, add mulch, such as Red Tomato Mulch.
  • Keep your garden records: Some crop varieties are more receptive than others to blossom-end red.

Whether it’s just minute black spots in the field or if it’s even worse, it makes your tomatoes look like rotting, the name of this disease is ‘blossomed tomatoes and red’.

It’s a disease that is not caused by some kind of pathogen, despite its pretty scary name; It is caused by a lack of calcium primarily because the nutrient does not enter the fruit even though the plant has enough calcium. Only by applying calcium fertilizer to the soil, this issue can be fixed in serious cases. Preventing blossom end rot on tomatoes can give you a tough fight. 

We’re going to take a look at the root cause (no pun intended) of the problem in this post, in reality, there are three potential causes, each of which is very easy to address. Therefore, within minutes of reading this post, you can stop any additional blossom end rot in your tomatoes.

If you know for a fact that one of the following three conditions affects your tomato plant, you can skip to the related section to learn more about it:

Get to identify the cause of the issue

We’re going to take a look at the root cause (no pun intended) of the problem in this post, in reality, the three potential causes, each of which is very easy to address. Therefore, within minutes of reading this post, you will stop any additional blossom end rot.

If you know for a fact that one of the following three conditions affects your tomato plant, you can skip to the related section to learn more about it:

What is the main causes of blossom end rot in tomatoes?

This condition is induced during its growth and development by a lack of calcium that enters the fruit. For the nightshade family, calcium is an essential micronutrient that includes, among others, tomatoes, eggplants, peppers, and okra. You might also face blossom end rot on tomatoes in containers. 

Must Read: Planting and Growing Okra Step by Step

It plays an essential part in the epidermis, that is, the fruit’s surface. There is no protective covering that can be formed when the fruit does not receive its due number, and the fruit grows without this cover and thus becomes black and hard. This occurs at the bottom of the plant, as the plant develops outward from the tip in this family.


Moisture plays a vital role in creating this problem, excess or less of moisture can affect the plant and thereby cause blossom end roots.

Soil too Cold at Planting –

Cold soil will interfere with nutrient absorption to the plant, which is more of a concern for northern gardeners.

Root damage from cultivation –

The roots can be harmed by vigorous digging around your plants (for weed control, for example). It will also conflict with the taking up of nutrients.

Soil pH too high or too low –

Any extreme pH will make your tomatoes difficult to thrive

Susceptible varieties –

Some tomatoes varieties are more resistant to blossom end rot than others.

Too much Nitrogen –

Dump a load of fresh manure onto your tomatoes, and you can be rewarded with loads of green growth and black bottomed berries. The nitrogen salts can make the tomatoes less accessible to the calcium in the soil.

Also, you can try water cones or soaker hoses to offer slow, steady water supply. If caught in heavy rain, drain the trench away from the tomatoes (if possible). Fresh roots above the sodden ground may also be promoted by heaping compost around the tomato plant’s foundation. (When the soil is too saturated, roots will drown.)

Pot grown plants in particular, due to difficulty keeping the soil moist enough, may be more vulnerable to end rot in bloom. Try the self-watering containers in your jar or water the spikes.


Tomato plants love the sun and prefer temperatures above 65 ° C (18 ° C). If you plant your crop late in the season, the soil will probably drop below this temperature during the fruiting time of your plants. They are not performing at their best at lower temperatures, and their roots do not absorb nutrients very well from the soil.

For plants in a greenhouse, painting with straw or leaves will reduce the temperature, thus putting black plastic sheets around your plants will help to warm the area and preserve the heat compared to the exposed soil. This is beneficial if your plant is late and the temperature has dropped.

If you have black container plants, you can paint them white to absorb less heat or instead cover them in aluminium to reflect the sun’s rays. As in a greenhouse, you’ll want to use a mulch to hold moisture and not lose it because of the sun.

The way of watering

Watering abnormalities is the most common cause of the blue end of your tomatoes. Perfect water conditions in containers are extremely difficult. The field needs to be moist enough and not damp until a few centimeters below the soil. This helps the plant to retain water when transpiring and thereby retain nutrients in the soil so that they are able to grow and spread around the plant.

If the roots become too dry, calcium, in this situation, will not absorb nutrients. The roots do not work as they cannot respire while the soil is soaking. The roots can also start to rot in prolonged cases.

Stress from other sources

The other reason the plant should be stressed is the chemical composition of the soil, other than temperature. Overfertilization or calcium deficiency in tomato plants causes a lot of stress on the plant and roots may totally stop the lockout of absorbing nutrients so that concentrated nutrients which could destroy a plant are not absorbed.

A lack of nutrients is not the cause of blossom end rot even though it is a concern unless it is due to a very rare situation of lack of calcium in the soil. You’ll have to have your soil tested, to know for sure. Using any calcium fertiliser in small amounts does not cause any damage.

A lack of enough calcium results in weaker cell walls that can cause the fruit to crack until it is completely ripened. You can try adding calcium to tomato plants for a better blossom. 

If you are considering the addition of fertilisers, other than the above points, it is helpful to know at this stage of growth, what kind your plant should use. You should read my manual on fertilising tomatoes to learn more about this.

High nitrogen consisting fertilizers are the reasons

behind your tomatoes suffering from blossom end rot. It will take some time before you can fix this problem because calcium takes time to climb up to the entire plant system.

Does adding calcium to tomato plants help?

There are two separate tissues in plants, the xylem, and the phloem. The first is for the transport of water and nutrients, while the second is for the transport of molecules of food or energy produced during photosynthesis.

Also Read: Growing Tomato for Your favorite Cuisines

Leaves do not have xylem tissue, and calcium is an essential resource that is picked from the soil and passes through the xylem tissue and not through the phloem. This calcium would not move to the fruit if sprayed on the leaves.

Unlike the leaves, the fruit has no stomata (used during transpiration to exchange water and air) and thus has no real openings for something sprayed to get into the plant and pass through it.

More about blossom end

As Blossom end rot (BER) occurs, you can notice some dark spots on the bottom of the tomato as it grows. Gradually it starts becoming leathery and black and may even cover the entire bottom of the fruit. 

Blossom end rot is often attributed to a lack of calcium in tomatoes, either due to exhausted, poorly drained soil or simply of displacement due to transpiration, especially when plants are under stress. Technically this lack of calcium causes brown spots on blossom end rot tomatoes. For this reason, it is always recommended that you add calcium to the soil or substitute, the calcium in the plant with a foliar application will help to fix the issue. But it’s rare for calcium to be absent from soil. Instead, there may be a variety of other environmental causes of end rotting of the tomato bloom, from uneven watering due to drought, heavy rainfall, or overcare of a gardener.

It is also crucial to provide sufficient and even quantities of water for tomato plants. While keeping the soil and plant roots insulated, the addition of mulch will help maintain moisture. Although it may or may not be effective, and is a widely debated topic, it may not necessarily hurt to add crushed eggshells, limestone, or calcium carbonate to the soil, but it may not help much either.

Quick tips for a great blossom

  • Try to apply calcium to the soil before planting the plants in the field or containers, using lime or gypsum. When Blossom End Rot occurs on the fruit, Calcium nitrate, water-soluble lime, hydrated lime, and very fine lime can be applied (top-dress and light raking) to help correct potential fruit from being affected. 
  • Increase timely irrigation to establish healthy soil moisture. Apply mulch to tomatoes which will help to preserve soil moisture.
  • Do not overfeed the plants, particularly with a fertiliser high in nitrogen.
  • Use all-purpose garden foods that are lower in N and higher in potassium and phosphorus, and other nutrients, including calcium, that are required.
  • Verify the levels of its pH. –
  • The movement of calcium/water into the plant and fruit would also be influenced by cold temperatures (soil and air). Another good excuse for not planting tomatoes in the season too early! When temperatures get colder, plant them.


At some point of time in the entire life-span of the tomato plant, it does go through blossom end rot, no matter which variety of plant it is. Although when the weather condition starts changing, this disease in the plant will clear up on its own. And yet if you find a plant deteriorating due to blossom end roots disease, then simply pluck and discard it. 

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