Tomato Blossom End Rot

tomato blossom end rot

Blossom end rot is fairly easy to identify because of the dry sunken decay of the blossom end of the fruit. The rot begins with a small water soaked area on the blossom end. A lesion develops and is followed by the leathery rotten area. Eventually it will cover the lower half of the tomato which will become flat or concave destroying the entire tomato.

Causes and Symptoms

A calcium deficiency is the most often cause of blossom end rot in tomatoes. The root cause of this deficiency is thought to be fluctuations of heat and cold weather and excessive rainfall. When these occur at the same time, calcium becomes unavailable to the plant.

Aggravating factors are soil with too high a PH (too acid), plants too close together causing a lack of air circulation, from over watering or from high humidity. Periods of drought followed by rain can cause blossom end rot also. The normal plant cells of the tomato require calcium to grow. When calcium levels are insufficient for growth, the plant tissue breaks down causing the “rot.”

Treatment and Control

You can’t do much about poor weather conditions so the best treatment and control is to do everything possible to avoid the problem. Get your soil tested for PH regularly. There are home tests available online for a very small fee. Ideally your soil PH should be 6.5 and this will provide adequate calcium. If you need to apply lime to improve the PH of the soil (and your extension office will generally give you a specific recommendation with your soil test results), it is best applied 3-6 months ahead of planting so you must plan ahead.

Plant your tomatoes at the correct time for your area. Too early planting could expose your crop to fluctuations of temperature that encourage disease.

Do not over-water your plants. Once your tiny plant is established in the ground, stress it slightly by letting it dry out in-between watering. This produces deep root system capable of drawing up nutrients from the soil. Plant seedlings far enough apart to allow good air circulation, pull out suckers to keep only 3-5 main stems and trim the bottom leaves off the plants. Use mulch to keep even moisture levels.

Use super phosphate fertilizer which is high in phosphorus and low in nitrogen. Work this into the soil before you plant. Also be sure to provide adequate drainage for tomato plants. Do not use excess potassium or magnesium fertilizers either because they compete with calcium uptake by the plant. Remember that Epsom salts is a magnesium source so it should be avoided unless you have had a soil nutrient analysis that indicates a deficiency.

Once the problem develops, it is very difficult to control. First try and stabilize the moisture level which will be difficult if you are in a rainy season. Some gardeners side-dress plants with well composted manure or water with compost tea. Others add crushed egg shells, bone meal tea, powdered milk to the plants but prevention is the key.

Comments from Other Gardeners
  • Theresa says:

    I’ve seen bone meal tea mentioned in several different places lately and have never used it. How do you make it, or where do you buy it? I would, of course, prefer to make my own, but if I need to buy it, I will.

    I assume that there’s a high level of calcium but should I use it all the time in my soil or only in certain circumstances?

  • Elise Rieschl says:

    In this article there is a common error when it was stated that a high pH was too acidic.
    Actually a high pH (a pH value greater than 7) is basic. Using lime will raise the pH, so depending on what the pH value is to start will cause the end result. Be careful, tomatoes do not thrive in basic soil.
    A neutral pH is 7, so 6.5 is slightly on the acidic side of the scale (a number less than 7 is acidic). Since tomatoes enjoy growing in slightly acidic soil this makes sense.
    If the soil is too acidic (example: a low pH value, such as “4.5” ), then of course tomato plants will not thrive, so it would be necessary to add a small amount of lime to raise the pH to approximately “6.5”.
    A local extension office should be able to assess whether the soil pH is in a desirable range for growing tomatoes. If the soil needs altering they should be able to suggest with what and how much and a method of proper application.

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