GROW WITH ABUNDANCE: Farewell to Blossom-End Rot

By Sommer Cartier.

There is nothing more frustrating than waiting all spring to harvest that first big, juicy, ripe tomato, only to turn it over and discover it has a soft dark rotten spot on the bottom. This condition is known as blossom-end rot and it is a common problem among home gardeners. In fact, it is one of the most common challenges to growing tomatoes. The disorder starts as a water-soaked spot that darkens and grows as the fruit develops.

Blossom-end rot is the result of a plant’s inability to access sufficient amounts of the calcium needed by developing fruit. The condition generally occurs when plants that have had a healthy productive start experience periods of sudden dry weather during the early stages of fruiting. An abundance of rain followed by sudden hot weather may also produce blossom-end rot because both excessively dry and wet conditions distort the ratio of calcium salts in the soil, making calcium less available to plants.

Once tomatoes show signs of blossom-end rot, they cannot be healed. With blossom-end rot, the focus must be on prevention and control. Below are several strategies that may be used to reduce blossom-end rot in tomatoes.

  • Apply fertilizer and calcium sulfate (gypsum) to your soil before planting tomatoes. For fertilizer, follow the instructions provided on the package. With gypsum, apply at a rate of 1 to 2 pounds per 100 square feet of soil area.

  • Before planting, test the acidity levels in your soil. If the pH is less than 6.0, add enough lime to bring the pH up to roughly 6.5.

  • Maintain consistent and uniform levels of moisture by irrigating as necessary.

  • Mulch plants. Use straw, woodchips, or anything that will conserve moisture and help control the temperature.

  • Be careful not to disturb the roots. If working the soil, stay at a distance of at least 1 foot away from the plant.

  • Select tomato varieties that are less susceptible to blossom-end rot. Celebrity and Big Boy tomatoes are highly resistant to a number of diseases and ailments, including blossom-end rot.

Follow these tips and you will surely be rewarded with a bounty of sweet juicy tomatoes this summer. Just remember, tomatoes can be a challenge to grow but they are a challenge worth taking! Nothing beats the flavor of a homegrown vine-ripened tomato.

Sommer Cartier is a certified Master Gardener with an MA in International Development and Social Change. Her specialty is working with local food systems and using gardens as a tool for community engagement.


Our Mission  To inspire and educate the people of San Diego County to grow and enjoy plants, and to create beautiful, environmentally responsible gardens and landscapes.


Our Vision   To champion regionally appropriate horticulture in San Diego County.

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