Master Gardener Sue Morris: Blossom end rot in tomatoes can also be internal

Sue answers a question asked at Kandiyohi County Fair about black rot inside tomatoes.


A question that surfaced at the County Fair this year was “why are my beautiful on the outside red tomatoes completely black when I slice into them?” “What am I doing wrong?”

I didn’t have an answer for this so I went online to see what I could find. Someone online had asked “Why are my Romas perfect on the outside but when cut into, the seed core is black with rot?”

There were two possible reasons listed. There is one form of blossom end rot that has no external symptoms but the interior tomato tissue can blacken and rot.

The answer to this was to treat the plant the same way you’d treat any plant with blossom end rot: provide even watering, regular fertilization and slightly acidic, well-drained soil. (I’d never heard of INTERNAL blossom end rot before.)

The other reason was that any break in the tomato skin, including tiny holes bored by insects, can let bacteria and fungi into the fruit. The microorganisms can eat away at the interior part of the tomato, leaving black or rotted spots.


Then another possible cause included anthracnose and black mold entering at wounds through growth cracks.

From the problem presented to me, the answer must be internal blossom end rot. I learned something new that day. I always thought blossom end rot appeared on the outside where the blossom dropped off. Why is this the first I have heard about this problem? Could just be all the hot dry weather is contributing to the condition.

We have been told when you have external blossom end rot, you can merely cut off the black portion and eat the rest of the tomato. I don’t think I’d eat any part of a tomato with the black rot on the inside.

It seems as though drought and heat have no negative effects on weeds in the lawn and/or garden.

Do you wonder what that weed is called that thrives in bare patches, disturbed areas and drier spots. It only lives for a year but can spread vegetatively or by seeds and its flowers are yellow in color but usually hard to spot. It looks like ground cover and lies close to the ground.

It is purslane.

A friend(?) one time gave me a seed packet of it as a joke. She had received it as a freebee with her garden order. Supposedly it can be used in salads. I wouldn’t recommend it.

It has been said that purslane was an introduced weed in Minnesota and was used by people in North America before 1492. There is one theory that Leif Erikson and the Vikings brought it over to this land around 1000 A.D. but the Norwegians disagree.


The best way to get rid of it is by pulling it out, but make sure you get it out of the garden when you pull it in case it has mature seeds.

It has been suggested you could try solarization by putting a clear plastic tarp over the area to heat up, dry out and eventually kill weed seedlings. I don’t think this would work very well as it sneaks in between rows and plants and would be hard to cover.

Wonder who we should blame for dandelions?

Related Topics: HOME AND GARDEN
Donna Middleton started working at the West Central Tribune in 1975 and has been the news assistant since 1992. She compiles the arts, health, farm and community page calendars, as well as rewrites and works on the special sections.
She can be contacted at or phone 320-214-4341.
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