Blossom-End Rot

One challenge that will be coming soon for anyone growing tomatoes is blossom-end rot. Blossom-end rot is a nutrient deficiency where the plant isn’t getting enough calcium. This in turn causes a disorder within the plant and causes its fruits to rot. This disorder most often occurs in tomatoes, peppers, eggplants and squash plants.


As calcium is a primary nutrient in helping build cell walls, a calcium deficiency will cause the cells in the fruit to break down and begin to rot. The result is that the blossom-end (i.e., the bottom of the fruit) will turn leathery and start to rot as it approaches full-size.


While the direct cause of blossom-end rot is a lack of calcium inside the plant, there may also be indirect causes:

  • Insufficient calcium in the soil – Add calcium fertilizer or lime to your soil as needed. Always amend your soil for calcium deficiencies well in advance of fruiting as calcium is generally slow to move where needed. Fertilize your plants using a foliar spray if the calcium is needed immediately.
  • Too much nitrogen in the soil – A plant will take up nitrogen at the expense of other nutrients. Cut back on any nitrogen-rich fertilizer for all but leafy greens when plants begin to flower.
  • Inconsistent watering – Plants take in calcium in solution form through water. Ensure consistent watering when plants begin to fruit. Using mulch helps to prevent water loss. Note that you don’t want to overwater as that may negatively affect plant flavour.


The best thing to do is to prevent this deficiency before it happens by adding a lot of calcium to the soil before the plants flower and by watering regularly. When your tomato, pepper, eggplant and squash plants begin to bear fruit, check the fruits regularly for dark spots – note that this is different than “corking”. As soon as you see any signs of blossom-end rot, throw out the affected fruit and use a foliar spray with calcium on the plant.