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How do the leaves look like?
I also suspect blossom end rot, but most soils have enough calcium, especially if you water with tap water.
Often, this is caused by a lack of airflow. If the plant can't transpire, not enough Ca is transported into the tips, which results in said symptoms.
Maybe remove some leaves and add a ventilator to give them some air current
Yes BER. Amish trick is to spray the tomatoes with milk - any dairy milk. It can be old or spoiled. The calcium in the milk is a rapid solution. It is also supposed to stop fungus problems too.
It is called "Blossom End rot". It is a common problem with tomatoes.
It is because of either lack of calcium or irregular watering.
If you have calcium deficiency, you can solve it by using egg shells, bake them for a few minutes in the oven at 120 deg. C, crush them and add some vinnegar to it and let it sit over night.
Then use the "juice" and mix it with 10 times it's volume water. Water your plants every other day with it and it fixes it.
Quick clarification.
BER is always caused by a calcium deficiency at the growing point.
This can be caused by 3 things: insufficient translocation of calcium from the roots to the growing point, lack of calcium in the soil solution, or calcium unavailable for other reasons.
Insufficient translocation: The most common cause of the disorder. A few different causes are possible: irregular watering, rapid temperature changes, sucking insects, or any damage to the root syatem (fungus, bacteria, insects etc.) It can also be genetically related for example the old OP Roma are notorious for it.
Calcium unavailable in the soil. This usually is related to pH. If the soil pH is above 8.5 or below 6.5 the plant can't take it up. Calcium like all other nutrients can also be temporarily locked up in the microbial community with high amounts of organic matter being broken down.
Lack of calcium in the soil solution. This is pretty rare for most gardens and the least likely culprit. Its the easiest to fix however so this is generally where most people start.
Most likely irregular watering. It is caused by calcium deficiency but the answer isn't to supliment with more most of the time. The calcium in the soil just needs the water to be able to move from the soil to the roots
Blossom end rot possibly! Need more calcium in the soil if so! Some tomatoes are also prone to it, unfortunately.
Not often the case, unless all fruits have it. For me, mostly it's just that on some very hot days the calcium can't be transported to the fruits. That's why you often see it on some of the first fruits too, not enough root system to properly support them yet.
Looks like everyone already diagnosed for you, so I'll recommend another solution. Cal-mag is a decent product that will help correct this.
@kinther looks like a lack of calcium. Caused by both over and under watering. What do the leaves look like?
Probably calcium
Aah. Tomato crunchy bits.
They are watered once a day and the soil dries out in between. Im thinking calcium
Going to agree with the other posts here, I experienced the same thing on my first wave this year. We had an abnormally wet early summer and nothing in my garden was a fan. Sometimes, shit just happens.
We had a two week period of no rain and brutal heat. Plants looked great but any fruit from that time had end rot. It's just tomatoes being fair weather. Top dress with some added bone meal and keep your water schedule rigid.
We dried out after the first wave set on, and I was able to correct the issue before the second blossoms set on.
Across the various sub's i've seen this question maybe 6 times in the past 2 months.
It must be tomato season.
Blossom end rot. Most common tomato disorder. Add more calcium to your soil; fastest way would be to go buy some fertilizer with calcium specifically, and if you have more time, to add some crushed limestone or shells to your soil. Bone meal is the most easily applied, fastest way to fix a calcium issue.