Why do Tomatoes Turn Black on the Bottom on the Vine?

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Why do Tomatoes Turn Black on the Bottom on the Vine

Just about every gardener who has cultivated tomatoes has had to deal with some growing issues. Sometimes tomato vines wilt, other times they’re destroyed by insects. But why do tomatoes turn black on the bottom on the vine? That’s a surprisingly common issue when growing these fruits. Fortunately, it can be avoided with some simple measures, treated once it shows up, and prevented in future crops.

Why do Tomatoes Turn Black on the Bottom on the Vine? What’s Wrong with My Crop?

Three words: blossom end rot.

If you’re not familiar with this issue yet, let’s take a moment to delve into it.

You know how tomato plants produce abundant flowers in summertime? Those will develop into the luscious, juicy tomato fruits we all know and love so dearly. In fact, the ovule (which is the female part inside the fruit that gets pollinated) is what grows into a tomato fruit. Furthermore, the bottom of each fruit has a little spot that use to have the flower on it.

This is what’s known as the blossom end. 

When the tomato plant is stressed, or has insufficient vitamins as it’s growing, then those black rot spots will appear at the bottom of the fruits. They’ll rot right on the vine, and disappoint anyone who’s been looking forward to a healthy, delicious tomato harvest.

How and Why Does Blossom End Rot Happen?

If a tomato plant has insufficient calcium as it’s growing, it may not develop the ability to seal off the scab when that blossom naturally falls off. Think of it like the flower version of an umbilical cord.

This type of calcium deficiency is most prevalent in dry periods. You’ll find it when a tomato plant is stressed by periods of drought in between watering cycles. As a result, make sure to water your tomato plants regularly: never, ever let the soil around them get completely dry. 

If you find that your first few tomato fruits are exhibiting signs of blossom end rot, try to treat the issue before it gets severe. 

First and foremost, water the soil around your plants really, really well. Then, get a few rolls (or a big container) of calcium-based antacid tablets like Tums or Rolaids. Poke three or four holes around the base of each of your tomato plants, about an inch deep. Next, pop one of those tablets into each of the holes, and cover them over again with soil. 

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Water the plants at soil level every morning, before the sun gets too hot. Then again as the sun is setting, unless it has rained over the course of the day. The calcium tablets will dissolve over the course of about a week, so repeat this process weekly for six to eight weeks. This will ensure that enough calcium seeps into the soil to nourish your plants, and regular watering will allow the plants to drink up that calcium.

If you’re lucky, this will nip the rot before it has a chance to establish itself through all your plants.

When and if you still see some tomato fruits with rotten bottoms, pick them immediately and discard them. You can toss them into the compost pile, as this isn’t any kind of pathogen that will affect other plants, but is rather a symptom of a deficiency. It’s not contagious, but tomato plants grown in the same container or garden bed may suffer from the same deficiency.

Prevent This Issue in the Future

As mentioned, all of this is caused by irregular watering during the growing period. If you don’t water regularly, your tomato plant’s won’t get sufficient nutrient uptake. To prevent this, make sure that you work a lot of calcium into the soil before you plant your tomatoes. You can do this by adding agricultural lime to the soil.

The downside to lime is that it can increase your soil’s pH, which makes it more alkaline, rather than acidic. Tomatoes need acidic soil in order to thrive. As a result, you’ll need to also add amendments into the soil to maintain a soil pH of at least 5.5. Well-aged compost is an ideal choice, and you can also use sphagnum moss and coffee grounds to good effect.

Be sure to rotate your crops annually so you don’t plant your tomatoes in the same bed two years in a row. In fact, it’s a good idea to work on a four-year crop rotation system. This will ensure that everything you grow will have sufficient nutrients when it grows. 

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Now that you’re familiar with why blossom end rot issue occurs, you’ll be able to help others in turn! The next time someone asks “why do tomatoes turn black on the bottom on the vine?”, you can let them know exactly how to remedy their woes. And once you’re all growing happy, healthy tomato plants, you can save their seeds and share them with one another. Donate them to local community gardens too!

Not only does this ensure genetic diversity in everybody’s gardens, you can also rest assured that these varieties will grow well locally. And greater self-sufficiency benefits everyone around us!