Tomato bottom rot is a problem that many vegetable gardeners face. What causes that ugly black rot on tomatoes?

There is nothing like biting into a lush, ripe garden tomato that you have spent months growing. Discovering those prize tomatoes with large rotten areas on them is no fun, though.

However, sometimes those luscious tomatoes develop problems. What what causes those ugly brown rotten spots on them?

The main reason for tomato end rot is the inability of the tomato plant to absorb sufficient calcium to get to the fruit.

If this tomato problem plagues you, keep reading to find out more about blossom end rot and what you can do to prevent blossom end rot and alleviate it.

Blossom end rot cause

Even though tomatoes are one of the most commonly grown vegetables, they are susceptible to issues such as yellowing leaves, and lack of ripening on the vine. Today, we will learn about another issue – tomato bottom rot.

Tomatoes affected with this problem have a spot where the blossom once was. Tomato bottom end rot starts out with a small, water soaked area on the blossom end of the fruit, opposite the stem.

It looks like a small bruise.

Slowly, the spot will enlarge and turn darker.

The flesh will become black or brown in the area of the rot – and even turn leathery looking.

Eventually, half of the fruit may be affected.

Other vegetables which can also be affected by blossom end rot, although less often, are sweet peppers, squash, cucumbers, melons and eggplant.

This problem is not a disease but is considered a disorder caused by a calcium imbalance. Normally, the problem starts on the early fruit and affects fruits that have not reached their full size.

Fruits about half normal size will show this disorder first.

If your growing season starts out wet and then becomes dry as the fruit is setting, you are likely to find your tomato plants affected by it.

Tomatoes with blossom end rot, that are left to grow on the vine, will eventually begin to rot completely so they should be picked and discarded.

Some blossom end rot is likely to happen early in the growing season, since tomato plants are under stress when initially setting fruit.

Crop rotation can be a big help in preventing all types of diseases, including tomato bottom rot.

Blossom end rot is more common in tomato plants grown in containers, since they are more likely to have problems with sufficient moisture.

Determinate tomato plants are more likely to be affected than indeterminate ones.

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Why is there a calcium deficiency in tomato plants?

There are several factors that can limit a tomato plant’s ability to absorb sufficient calcium. These factors are some common gardening mistakes:

fluctuations in moisture (either too dry or too wet)
wrong cultivars of tomatoes chosen
extra nitrogen in the soil
poor cultivation resulting in root damage
too cold a soil temperature – This can also lead to catfaced tomatoes.
a soil pH that is too high or too low
lack of calcium in your soil

Tomato bottom end rot is nature’s way of telling you that the fruit is not receiving enough calcium, even though the soil itself and the plant’s leaves might have plenty of it.

The roots of the tomato plant has to be able to carry the available calcium upward towards the fruit. This happens when the plant is watered.

If you have had a dry spell recently, or are not consistently watering your plants, calcium is not properly drawn up to the plant, and blossom end rot may set in.

Prevention and control of tomato bottom rot

Since there are several reasons for a tomato calcium deficiency that causes blossom end rot, let’s examine these factors individually and see what we can do to prevent them.

Blossom end rot – tomatoes not being watered correctly

Inconsistent watering is the main cause of tomato bottom rot.

The best way to prevent blossom end rot is to plant your tomatoes in well draining soil and to water evenly. It is important to maintain consistent levels of moisture throughout the entire growing season.

Mulching tomato plants with straw, organic leaf mulch, or grass clippings will help soil maintain even moisture.

Water near the root area, rather than on the plant themselves to ensure healthy plants. Tomatoes need 1 inch of water, per square foot, each week and more if it is especially dry.

It is better to water thoroughly once or twice a week than a little bit every day to ensure deep growing roots. Soaker hoses or drip irrigation makes watering tomatoes easier.

Too much water is also a problem. If your tomato plants become overly-wet, they won’t be able to draw up the calcium to the fruit.

Tomato plant leaf curling, and tomato blossom drop, are also problems caused by inconsistent watering techniques.

Adding compost to your soil before planting helps the soil to drain well and keeps the plants from being waterlogged.

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Some cultivars are resistant to tomato bottom rot

Some vegetable cultivars are more tolerant than others of calcium deficiencies and less likely to show blossom end rot symptoms. Tomato bottom rot is seen more frequently in large cultivars and rarely a problem in small cherry tomatoes.

I have several types of tomatoes in my garden this year. My cherry tomatoes and Roma tomatoes show no signs of rotting problem. The Park’s Popper tomatoes, on the other hand are affected.

Choose cultivars wisely and check to make sure that the ones you choose can tolerate less calcium if blossom end rot is a common problem for you.

Celebrity and Big Boy tomatoes are resistant to a number of diseases and ailments, including blossom end rot. They are a good choice.

Also, consider growing indeterminate tomatoes that produce fruit until late fall, instead of determinate tomatoes that produce it all at one time and earlier in the season.

Excess of nitrogen in the soil might cause bottom end rot

Too much nitrogen in the soil can cause lush growth of leaves at the expense of fruit development. It can also lead to blossom end rot.

Use fertilizers that have a low nitrogen content but one that is high in phosphate.

Since blossom end rot is caused by calcium not reaching the plant, it may be tempting to fertilize your plant more. But don’t be heavy handed on the fertilizer. If you feed them too much, they may be growing too fast. This can prevent the calcium from being delivered quickly enough.

Also, remember that there is likely sufficient calcium in the soil – but the plants are not absorbing enough of it.

Over-fertilizing can actually make tomato bottom rot worse. Consistent watering is almost always the solution.

If you do decide to fertilize, choose one that is formulated with more calcium and use a fertilizer that has a high middle number on the label. This will show you that the fertilizer has high phosphate and low nitrogen. (example – 4-12-4, or 5-20-5)

Soil cultivation is important in preventing blossom end rot

Take care to avoid cultivating the soil too near to the root area. A light tilling is all that is needed for controlling weeds.

Also, if the roots of your plants are crowded, this will limit their ability to draw calcium up to the fruit. Space tomato plants well to give the plants and their roots room to grow.

Be sure to stake your tomato plants when they are young to avoid damaging the roots by adding a stake later in the season. I stake my tomato plants as soon as I place them in the ground.

Soil too cold can be the cause of tomato bottom rot

Many gardeners are eager to experience the taste of early spring tomatoes. However, if you plant then too soon, your tomato plants will be growing in cold soil and this is a the perfect scenario for blossom end rot.

Plant at least two weeks after the last frost date in your area. Be sure the soil is at least 60°F before you transfer your tomato plant seedlings outdoors.

A soil thermometer will help you determine the temperature.

Soil pH problems and blossom end rot

Like most vegetables, tomatoes like a well draining soil high in organic matter with a pH of about 6.5 -7.5 (slightly acidic to neutral) since this gives the plant the best nutrient uptake.

If your soil is too either too acidic or too alkaline, this can lead to blossom end rot.

While there are some DIY ways to test soil pH, the most accurate way to do this is with a soil pH meter. Testing is even more important if you use lime as a source of added calcium.

Lack of calcium in your soil

In spite of following all of the tips above, you may still find tomatoes with blossom end rot. A lack of calcium in your soil, although not common, is a potential cause. Soil testing is the way to learn this.

This is most likely to happen if you are using older soil where the calcium levels might be depleted.

You can use soil testing kits or contact your local Department of Agriculture for help on soil testing. If soil testing shows that your soil lacks calcium, add lime, bone meal, or finely crushed egg shells to add more.

Fixing tomato bottom rot

Unfortunately, once a tomato has blossom end rot, you can’t fix it. The problem will not go away on the affected tomatoes. There is no such thing as a tomato bottom rot cure.

However, you can still save the plant and any remaining tomatoes that it produces.

Remove all of the tomatoes with bottom rot from the plant and toss them on the compost pile.

If the damaged portion of the fruit is small, you can trim it off and enjoy the rest of the tomato. It is safe to eat and it’s easy to see which part is affected.

The tomato bottom rot does not spread from plant to plant, or even among fruits on the same plant. If early tomatoes are affected, later ones may be just fine.

There is no point in using fungicides or insecticides, since this is a disorder, not a disease.

Will adding egg shells help with tomato blossom end rot?

Egg shells have lots of natural calcium. Will adding them around the plant fix tomato bottom rot?

As egg shells break down, they can, indeed, add calcium to the soil, but not until they begin decomposing, which is months away.

Also, as noted above, the problem is not normally caused by an actual lack of calcium in the soil. Rather, the calcium won’t get to the fruit.

The answer is simply to water more.

Keep the faith!

Even though the appearance of heavily damaged tomatoes can be discouraging, keep the faith!

The best cure for tomato bottom rot is preventing it in the first place. However, with careful maintenance, it can be reversed, even if you lose a few early tomatoes to it.

Pin this post for tomato bottom rot

Would you like a reminder of this post about blossom end rot on tomatoes? Just pin this image to one of your gardening boards on Pinterest so that you can easily find it later.

You can also watch our video about the disorder on YouTube.