What is this black or brown spot on the bottom of my tomato?


Nothing shocks a beginning or experienced a gardener more than a blemish on the tomato they spent a ton of time and effort growing.  If you see a dark brown or black spot on the bottom of your tomato you most likely have blossom end rot.  The blemished tomatoes are still edible.  Cut the blemished end off and the rest of the tomato is fine.

First, don’t panic, it is a temporary condition.  Typically only the first few tomatoes of the season are affected.  As the season goes on subsequent harvests should be blemish free.

Blossom end rot is caused by a deficiency of calcium in the soil.  It can also be caused by low pH in the soil and by severe fluctuations in water both drought and too much rain can cause these blemishes.  With a lack of Calcium plants are unable to go from periods of drying out to having too much water.

It is easily prevented, although the key word is prevented.  Pay attention to your watering; do not let it dry out completely, aim for a consistent soil moisture level.  You can add mulch around your plants to prevent evaporation even in dry spells.
Gardeners have been adding Bone Meal  for over a century.  When planting your tomato, sprinkle some Bone Meal into the hole you dug for your plant, work it into the bottom and sides.  Organic gardeners have also used egg shells, which are mostly Calcium.  Store eggshells through the winter in the freezer, and crush them to save room.  When planting time comes, pulverize into small pieces and line the bottom of the hole. 

If you get blossom end rot this year, odds are it will be back.  However if you use the tips we mentioned next spring, you can improve your odds for a better harvest next year.