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Water Can Be the Cause of Tomato Problems

University of Minnesota Extension, Stearns County News
July 13, 2016        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties


Water Can Be the Cause of Tomato Problems
By Beth Berlin, University of Minnesota Extension

LITTLE FALLS, Minn. (7/13/16) — With the recent heavy rains in many parts of Minnesota it is a good time to discuss the issues water can cause in our gardens.  For tomatoes, water, especially irregular or overwatering can cause blossom-end rot.

Blossom-end rot is actually not a disease but rather a calcium deficiency in the tomato. For most it isn’t a lack of calcium but rather environmental or cultural conditions that prevent the plant from properly up-taking calcium. This may be caused by over application of nitrogen or irregular or over watering.  When a rapidly growing fruit is unable to get necessary calcium, the tissue breaks down, leaving the sunken leathery black lesion at the blossom end.

Symptoms often begin as a small water-soaked area at the blossom end of the tomato.  These symptoms may even appear at any stage of growth, but is most common when the fruit is one-third to one-half its mature size. The lesion develops, enlarges, and becomes sunken and black with a leathery appearance. In severe infections, the entire lower half of the tomato may become flat or concave. A decay bacteria typically infects the lesion and will result in rot.

Here are some tips gardeners can do once they have planted their tomatoes to help prevent blossom-end rot:

  • Encourage larger root systems by keeping the plant a bit dry for the first few weeks after planting. Discontinue this practice once it begins to flower. Stronger, larger root systems allow the plant to reach more nutrients and water in the soil versus a shallow root system.
  • Once fruit begins to develop, keep soil evenly moist. Avoid overwatering and extreme fluctuations.
  • Apply two to three inches of mulch under the plants to help maintain even moisture and keep soil temperatures cooler
  • Do not over fertilize, avoid high-nitrogen fertilizer which can cause calcium uptake issues as well as result in large bushy tomatoes without fruit.
  • Avoid cultivating near plant to prevent root damage.

For more information on growing tomatoes visit With persistent, diligent care gardeners can enjoy a plentiful crop of tomatoes.