GROW WITH ABUNDANCE: Farewell to Blossom-End Rot



Blossom-End Rot.  Photo attribution: KBR.

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.