Your Questions Answered: Black Bottomed Tomatoes

Question: I am having a problem with some tomato plants in my back yard. The plants are growing good and strong and small green tomatoes are begging to grow. I looked at the bottom of one tomato and it is turning black. Can you please tell me what is causing this. There are several tomatoes on the vines of this plant, but only one tomato has this black section on it.
- George K.

Answer: Hi George,

Your black bottomed tomato sounds a lot like blossom end rot. I don’t have a picture of it to post but a quick search will bring up countless photographic evidence for identification. The reason I am ruling out other problems is because you describe your plants as healthy. Blossom end rot appears as a blackened, sunken spot on the bottom of green or ripening fruit. The plant itself rarely shows any signs of a problem. In fact some stricken fruit is found growing on plants that are exceptionally leafy and health. This particular brand of the condition is a symptom of excessively fertilizing with a high nitrogen fertilizer. In that case, much of the plant’s energy goes into producing big, healthy leaves, leaving little else for fruit production.

Blossom end rot is a very common condition said to be caused by a calcium deficiency, however in general the problem is not caused by a lack of calcium in the soil but inconsistent watering, drought, and uneven soil moisture making it difficult for the plant to draw nutrients up through the roots.

From your description it sounds like your tomatoes are growing in-ground however this problem is especially common for container grown plants since containers dry out quickly and can be difficult to keep consistently watered.

The good news is that the problem is easily fixed — future tomatoes grown on the same plant aren’t doomed to be diseased if you follow the advice below.

General Tips to Avoid Blossom End Rot

  • Amend poor soil by adding lots of organic matter like compost. This will provide better nutrition for the plants and make for soil that holds moisture well.
  • Water tomatoes deeply, but less frequently. This means give them A LOT of water when you do water rather than watering regularly but in small quantities.
  • Water more often once your plants start to produce fruit, continuing to water deeply each time. Tomatoes are a watery fruit, your plant will need lots to grow healthy fruit.

When Excessive Nitrogen is the Problem

  • Cut back on high nitrogen fertilizers like fish emulsion.
  • Add kelp meal or liquid seaweed to ergular waterings. You can even spray the blossoms with this mix when they first open.

Tips for Container Gardeners

  • When growing in a container, grow only one tomato plant per pot.
  • Choose a container that is appropriately-sized for the plant. Small busing and dwarf tomato plants will do in a hanging basket but most tomatoes have very deep and ample roots requiring lots of space. Garbage bins are the way to go.
  • Grow tomatoes in plastic pots when possible. Plastic retains water much better than terracotta, a difference that will become much more noticeable at the peak of summer drought.
Gayla Trail
Gayla is a writer, photographer, and former graphic designer with a background in the Fine Arts, cultural criticism, and ecology. She is the author, photographer, and designer of best-selling books on gardening, cooking, and preserving.

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11 thoughts on “Your Questions Answered: Black Bottomed Tomatoes

  1. I cured mine by something my grandfather use to do. I ground up egg shells in a jar and filled it with water overnight. Then dump the water and shells around the base of the plant. The calcium from the shells leeches into the soil every time it rains. Walla, no more end rot (over time).

    If you are vegan, you can ask your local organic farm to save eggs they can’t sell in time for consumption for you. They are usually free range and organic so you supporting the harmful practices of factory egg layer eggs.

    I have sea shells laying in my pots which seems to help on multiple levels, replenishing calcium as they break down plus when I am forced to use the hose I have something to aim it at so it doesn’t disturb the roots.

    Shell Greenier

    http://Shellberry.etsy.com
    Shellberry, an Urban Homesteading Co.
    http://www.WereAllMadHere.com
    Artifacts of the Madness

  2. I’m so glad this got posted – I’ve been having a similar problem with my yellow squash. I assume the same goes for other plants, not just tomatoes? I water regularly (and we’ve had a wonderfully wet spring) and my dirt has been gardened well and is nice and black. (All my tomatoes and other plants are just loving it.) The plants are growing so well – the leaves and blossoms are nice and big, but the weird thing is that I’ve already harvested 3 *huge* and delicious squash, the rotting black ones show up randomly. Any suggestions for something like this?

    Thanks a bushel!
    Amanda

  3. Blossom end rot, is caused by a lack of Calcium, itself due to lack of water.

    Basically it is too hot for the plant and rapid transpiration means it can’t get enough water (containing Calcium) up from it roots. Covering with fleece will help. It will reduce water loss and also growth – the later will make the fruit tastier.

  4. I’ve heard that planting the seedlings deep, well up to the first set of leaves, helps promote a healthy root system better able to get water. Since I’ve done so, there’s been very little blossom end rot.

  5. I have eliminated this problem with my tomato plants by being extremely consistent about watering. Also watering deeply, at the base of the plant only (not touching the leaves) has just about eliminated the spread of blight.

  6. Gack! Thanks for a VERY timely article.

    This never happened to me before except for a volunteer tomato growing in a blighted bed last year… but this year, it’s everywhere; all my full-sized tomatoes in containers are affected (not in the ground, or the cherries)!

    I’m worried that I mixed in a lot of worm castings and I have tremendous gorgeous foliage… and the thickest, sturdiest trunks you could imagine. It may also have been because of all the rain we had this spring.0

    Anyway, I thought the jumbo size of the plants would bode well for the quality of the fruit, so imagine my horror to discover the ends rotting today… :-(((

    Will attempt to water consistently and also spray kelp meal liquid directly on the blossoms.

  7. Is it wrong that when I read this, I sang, “Black Bottomed Maters make this rocking world go round!”?
    Yes?

    Right.

  8. One quick question: is it better in terms of potential future good-fruit production to pull off the BBMs (black-bottomed maters!) when the end rot first appears or let them go all the way, so to speak?

    I have been pulling mine off, because they’re so sad to look at, and bc there’s no point letting them ripen all the way. Will this damage the plant in some way?

    Tks!

  9. Jennifer: Remove them. They will grow a bit but the rot will spread. Better to allow the plant to put that energy into healthy fruit.

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