Why are the bottoms of my tomatoes brown?

Recently in the garden, we noticed that some of our Cherry and Roma tomatoes were developing brown ends on them. This, unfortunately, is known as Blossom End Rot it is a disease caused by environmental conditions that affect the bottom of the tomato fruit. The rest of the plant will appear to be healthy. No damage to leaves or stem occurs

  • Usually, blossom end rot shows up when the fruit is green or beginning to ripen.

  • Calcium deficiency is the most common cause of tomatoes. The deficiency comes from fluctuations in hot and cold weather accompanied by excessive amounts of rain. When this happens, calcium becomes unavailable to the tomato plant

  • If the tomato plant gets too dry or is given too much water over a period of time, it becomes harder for it to absorb calcium from the soil, leading to deficiency. Calcium is absorbed by the plant as it absorbs water. (No water intake, no calcium intake)

  • Tomato plant cells require calcium to grow, when there isn’t enough calcium for growth the plant tissues begin to break down causing rot. (when the demand for calcium exceeds the supply, the tissues break down.

  • Contributing factors are extreme fluctuations in the amount of water the plant has access to, temperature fluctuations, soil pH is too high or low, poor air circulation between plants, overwatering, high humidity

  • Drought followed by rain is also a cause


  • Easy to identify.

  • It is characterized by decay of the blossom end of the fruit (the bottom)

  • The bottom of the tomato turns tan in colour, it softens and then turns black, sunken and rotten

  • Can grow to cover half of the tomato

  • Blossom end rot can not be transmitted from plant to plant or by contact.

  • However, it is more than likely that it will affect the fruit-bearing plants in the same planting location because of common exposure to the same environmental conditions

  • Prevention:

  • establishing a soil pH around 6.5 will allow for calcium uptake,

  • establish and maintain a stable watering routine

  • Be careful not to overwater and to avoid drought-like conditions

  • Irrigation and mulching around tomato plants can help to retain moisture in the soil when drought is a concern.

  • Make sure to add mulch after the soil has warmed up in the spring. If you add it too early it will act as an insulator and the soil will stay cooler longer

  • Crop rotation.



In addition, waiting to plant tomatoes until it is warmer can reduce the risk of blossom end rot developing. Plants that are transplanted while the soil is still fairly cold have an increased risk

  • Blossom end rot is more common in the fruits that develop first if the plant was planted in cold soil

  • More common when tomatoes that are grown in pots and raised beds because the soil gets drained of nutrients (Calcium in this case) faster

  • Limestone/water mixture to add instant calcium to soil (can raise the pH) bonemeal will help soil with calcium deficiency

  • You can still eat the part of the fruit that is not rotten

Did you know?

You can learn more about tomatoes and and other plant diseases through more of our blogs!


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