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Why Are My Tomatoes Black Inside – Causes & Fixes

Producing healthy ripened tomatoes is not an easy task. There are a variety of diseases and pests notorious for affecting the health of tomato plants. When you find what appears to be a healthy tomato to be discolored inside, you immediately wonder what it is and what caused it. So what many gardeners want to know is, why are my tomatoes black inside?

There are a few reasons a tomato may be black on the inside. Possible causes include blossom end rot, overripening, bacterial diseases, or early blight fungus.  

Read on to learn more about why your tomatoes may be black on the inside and best gardening practices to prevent disease.

4 Reasons Why Tomatoes Are Black Inside

Usually there are four main reasons why tomatoes may appear black inside.

Black Seeds = Overripe

If the flesh of the inside of your tomato is healthy and only the seeds are black, it is most likely that your tomato is overripe. This problem can happen when heat conditions are extreme, causing the inside of the tomato to ripen faster than how it appears on the outside; paying attention to weather patterns and harvesting more heavily before a heatwave can help prevent tomato seeds from turning black.

Blossom End Rot

Blossom end rot is a disease that affects tomatoes when the plant lacks sufficient calcium. The lack of calcium causes a localized rotting of the fruit, identified as blossom end rot. As blossom end rot develops, a section of the fruit sinks in and darkens, making that area of the tomato inedible.

Typically blossom end rot affects less than half of an infected tomato. The rest is still edible, so while it’s an annoyance, it does not mean your entire tomato crop has failed.

Blossom end rot can be prevented by a consistent watering schedule, mulching, knowing your soil pH levels, and fertilizing appropriately. Consistent water helps distribute calcium that most likely already exists in your soil throughout the entire tomato plant.

Mulching helps to keep nutrients and moisture in your soil, slowing evaporation. A soil test can help you find an appropriate fertilizer for your soil conditions. Soil pH between 6.5 and 7.5 is ideal for growing tomatoes.

In addition to these preventative measures, one can prevent blossom end rot by avoiding tomato varieties that are more susceptible to the disease. Cherry tomatoes are less likely to develop blossom end rot than some types of beefsteak, Roma, and pear tomatoes that are at higher risk of developing the condition.

Bacterial Disease

There are a few bacterial diseases tomato plants are prone to that can cause blackening inside a tomato. These diseases include bacterial canker, spot, and speck, all of which affect the vascular appearance within the fruit and can often be identified on other parts of the tomato plant.

There are variances in symptoms among these three diseases that can help you determine which condition may be affecting your tomatoes.

These diseases are often brought into home gardens via contaminated seeds and transplants. Knowing that the source of your tomato seeds and transplants is practicing healthy cultivation processes is vital to keeping bacterial diseases from invading your garden.

In addition to coming in on the plant or seed itself, these diseases can live on garden tools and equipment for months. Regular sanitation procedures of these supplies are essential to maintain a healthy, disease-free garden.

If you do find yourself faced with one of these bacterial diseases in your home garden, it is best to let it run its course and salvage what you can of your harvest as these diseases are untreatable.

Tomatoes that show any sign of the disease should be thrown away and not eaten or composted. Sanitize stakes and tools that came into contact with the diseased plants and plant your next year’s tomato crop in a different section of your garden.

Bacterial Canker

Bacterial canker is a fairly severe disease for tomatoes as it spreads quickly and can easily take out a whole crop. It can affect the vines, leaves, and fruit of the plant, often beginning with the wilting of its leaves. As the disease continues to spread, it can cause the stem to split, and round spots appear on the outside of the fruit. The yellow-brown spots on the outside of the fruit could mean the disease has reached the internal vascular tissue causing blackening on the inside.

Bacterial Spot

Bacterial spot first announces its presence through yellow and brown round spots on the tomato leaves. As the disease progresses, the leaves begin to brown and dry out. Once a bacterial spot begins to infect the fruit, it can cause raised mole-like areas on the outer skin that can be rough to the touch. If it reaches the inside of the tomato, it can cause blackened areas making the fruit inedible.

Bacterial Speck

Bacterial speck first appears as small black spots on the leaves of a tomato plant. These spots are often on the underside of the leaf, so they can easily go undetected initially by its cultivator. As the disease spreads, the small black spots on the tomato leaves will also spread to the skin and often the flesh of the fruit.

Early Blight Fungus

Early blight fungus is a common tomato disease in high moisture growing environments. Early blight weakens the tomato plant resulting in a smaller harvest, or in more extreme cases, death of the plant. Early blight typically appears when plants are more established, either when flowering or with ripening fruit.

It first appears on the leaves of the plant with yellow and brown spots, similar to what appears with bacterial spot disease. However, in the case of early blight, the yellow and brown circles are concentric. As the disease progresses, these affected leaves will turn brown and die off.

When early blight gets to the vines of the tomato plant, it will develop dark sores that will also display a concentric circle pattern as the lesions expand.

When the fungus spreads to the fruit of the plant, its effects can be similar to what we see in blossom end rot in that it stays in one localized area of the tomato. On the stem end of the tomato, early blight fungus will appear with another concentric circle pattern as seen on the vine and leaves. These areas darken, become tough and begin to sink into the fruit.

Early blight fungus can be prevented with a few different practices. Ensuring that plants are spaced appropriately apart from each other can help to maintain consistent airflow, controlling moisture.

If you are experiencing a high moisture weather pattern using fungicides can help, but if any signs of blight are already appearing, it is best to remove the entire plant to prevent the disease from spreading. In addition, as mentioned with bacterial diseases, knowing your seed and transplant cultivator’s practices are healthy and regular crop rotation is best practices to prevent early blight fungus.

Final Tip for A Healthy Tomato Harvest

We’ve touched on a number of diseases that can affect tomato plants, but believe it or not, there are quite a few more. While tomatoes are one of the most common home garden plants, they are also known for being some of the most challenging to grow because they are pest and disease-prone.

If you’d prefer to avoid some of these potential challenges with growing tomatoes, there are some that have a higher resistance to diseases. There are many resources available online that group tomato varieties by least and most disease-prone that can be helpful as you plan your garden.