Tomato, tomaaahhhto…. Why does it rot(o)?

Thanks Doug for getting the question ball rolling…

Do you have any idea what I’m doing wrong with my tomatoes? They look like they are rotting from the inside out. They are heirloom San Marino variety. I am growing them in full sun on the south side of the house, in Edmonds, WA. This year, I tried something new. I planted the tomatoe plants around a 5 gallon bucket that was buried in the ground. I had drilled a bunch of holes in the bucket, an filled it with compost. I watered the plants by filling the bucket with water.Thanks – Doug MacKay

In 2015 my cropping assignment in school included growing 1000 tomato plants from seed. Remind me never to do that again. By the of the quarter I couldn’t stand the smell of a tomato plant… But I did learn a few things along the way.

After asking a few clarifying questions and getting a few more photos from Doug, I believe that this is a classic case of “blossom end rot”.

Generally, blossom end rot is the result of Calcium (Ca) deficiency. Often the Calcium deficiency is the direct result of the plants inability to transport Calcium to the plant tissues.

Two (2) causes that contribute to this problem include inconsistent watering – leading to a drought/water cycle and /or too much nitrogen in the soil.

Symptoms may include a decaying area at the blossom end of the fruit – the area furthest away from the stem. The pictures Doug provided clearly show this. 

Not all fruit are necessarily affected as the tissues involved are mainly low or non-transpiring tissues furthest away from the stem. Plants need a continuous supply of calcium as they grow. Since calcium does not move about the plant, it must be present in the tissues of the flowers and fruit all through the season. Consistent watering assists with this process by ensuring continuous transpiration.

Transpiration is the process where plants absorb water through the roots and then give off water vapor through pores in their leaves. An example of transpiration is when a plant absorbs water in its roots.

Source: The American Heritage® Dictionary of the English Language, 5th edition Copyright © 2013 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved. Read more at

Sometimes rapid growth from high-nitrogen fertilizers may exacerbate blossom end rot. Nitrogen causes fast growth of the foliage and the disease is especially prevalent when rapidly growing, succulent plants are exposed suddenly to a period of drought. 

From Dougs description above, his issue may have been the direct result of the change he made this year with the addition of the bucket of compost as an interface to his watering routine. While I cannot be certain of the c:n (carbon/nitrogen) ratio, it is possible that the leaching of nitrogen from the bucket through the watering process is creating an imbalance and thus contributing to the blossom end rot problem.

It sounds like Doug had water management under control and thus prevented water stress (drought stress), which can be a contributing factor in the plants inability to uptake calcium into the tissues. While the concept appears to be sound, substituting a material other than compost may be a more viable solution. Maybe filling the bucket with a soil/sand mixture and distributing a vegetable fertilizer via that system.

**Edit… One thing I forgot to mention, even though it appeared that Doug had watering under control, we did have a number of very hot days in the area. IF nitrogen was the issue causing foliage growth, it may have been helpful to water (even a bit extra) prior to the onset of high temperatures to ensure enough water was in the soil to assist with the transpiration process.

A symptom of transpiration issues (and the transport of calcium) is curled or brown edges on the leaves.

We saw this on a number of trees and shrubs around the nursery this year. We just couldn’t keep up with the watering due to the prolonged heat.

Some sources recommend spraying foliage with calcium chloride solutions. My experince has taught me that having the correct cultural environment and balance will go a long way in preventing problems thereby negating the need for treatments such as these.

Hopefully, this information helps.



Cornell Vegetable MD Online

Blossom End Rot Prevention and Treatment – Mother Earth News