[cc]

This is store tomato which I forget the name off.
If I remember correctly I have had this before but not a very start of harvesting. The tomatoes come of very easy. The leaves are also a little curled but very green and look otherwise in very good health.
Anyway see the picture.

[Aunt Sally]

Is that the blossom or the stalk end ?

[cc]

Is that the blossom or the stalk end ?

? Not sure what you mean. It's the bottom of the tomato?

[Subversive_plot]

The bottom of the tomato is the blossom end.

That is probably blossom-end rot (BER). It is a problem that could ruin a few tomatoes, but is not a systemic disease that will keep your plants from also producing good tomatoes.

BER is best handled through cultural practices. 
1. Any fruits showing this problem, remove and discard them.

 2. It is often caused by uneven watering, too little water at some times, too much at other times; try to keep the plants more evenly watered. My understanding is that the uneven watering can unevenly distribute nutrients, including calcium, throughout the plant and fruit.

3. Providing extra calcium can help. Lime the soil before the growing season, or provide gypsum, or calcium nitrate; aim for a neutral soil pH near 7 +/- 0.5.       

4. Some tomato varieties resist BER better than others. Flat-bottomed tomatoes seem to have BER more often, those with more pointed bottoms have less frequent BER.

[Aunt Sally]

Is that the blossom or the stalk end ?

? Not sure what you mean. It's the bottom of the tomato?

Ok, that’s where the flower was so possibly blossom end rot as SubP says.

[cc]

All tomatoes rotten up to now (4) moved outside yesterday (lack of room) have two more of the same tomato growing about a foot tall. I think I will pot them on into big pots. I must say watering has been pretty consistent this year. I have been consistent this year. Have been congratulationing myself. Never mind.

[Yorkie]

Not necessarily saying this is the case for you, but it's easy to think that if we water every e.g. 2 days, then we are providing consistent watering. However, it's about maintaining consistent levels of water in the pot, which means watering at inconsistent intervals - depending on the weather / temperatures.

[KalisDad]

The bottom of the tomato is the blossom end.

That is probably blossom-end rot (BER). It is a problem that could ruin a few tomatoes, but is not a systemic disease that will keep your plants from also producing good tomatoes.

BER is best handled through cultural practices. 
1. Any fruits showing this problem, remove and discard them.

 2. It is often caused by uneven watering, too little water at some times, too much at other times; try to keep the plants more evenly watered. My understanding is that the uneven watering can unevenly distribute nutrients, including calcium, throughout the plant and fruit.

3. Providing extra calcium can help. Lime the soil before the growing season, or provide gypsum, or calcium nitrate; aim for a neutral soil pH near 7 +/- 0.5.       

4. Some tomato varieties resist BER better than others. Flat-bottomed tomatoes seem to have BER more often, those with more pointed bottoms have less frequent BER.

Kali's Dad like this

[lettice]

Agree as above, that is down to irregular watering.
I water my tomatoes in and outside the greenhouse every evening.

Did suffer a little blossom end rot many years ago when I was away for a few weeks and the neighbour (I gave them watering instructions) did not water one particular outside crop of tomatoes in a couple of pots until later in the first week, as missed them.
The same variety a short distance away had the regular watering regime and did not suffer.

Would suggest cutting off the poorly tomatoes and the rest should be fine.

[cc]

I have watered every day so clearly nothing to do with inconsistent watering . Obviously God hates me! Or there is a deity for mice I have killed around 20 in the last month. Maybe I was getting to much pleasure out of it!

[lettice]

A useful page that sums it all is from the RHS;
https://www.rhs.org.uk/problems/blossom-end-rot

Just looked in all my old gardening books from the 50s/60s/70s and 80s and all mention the cause as irregular watering.

[jaydig]

I have watered every day so clearly nothing to do with inconsistent watering . Obviously God hates me! Or there is a deity for mice I have killed around 20 in the last month. Maybe I was getting to much pleasure out of it!

I agree with other comments that blossom end rot is due to irregular watering, but is it possible that your greenhouse has become extremely hot during the day and the soil possibly dried out a lot before watering?  If your greenhouse soil is very light perhaps either watering less, but twice or even three times per day, or setting up an electronic timer which will dispense water at set intervals might be the answer.

[Yorkie]

I have watered every day so clearly nothing to do with inconsistent watering .

This is the point I was making. In overcast cloudy cool conditions, you may only need to water every other day. In very hot conditions you may need to water twice a day.

It is not about watering at exactly the same time every day, irrespective of what the plant's needs are.  It's about watering at what may well be varying intervals, in order to maintain a consistent and appropriate level of moisture in the compost.

Daily watering irrespective of plant needs is perfectly likely to cause inconsistent levels of compost moisture and thus the risk of BER

[jezza]

Hello if you have the space consider a drip feed system with a watering controller that way you know that its going to be regular watering,we use to use drip feed at the market garden I worked at we grew  275,000 tomatoe plants 2000  cucumber plants, 1.4 million lettuce  over 5 crops ,1000 aubergines that had to be hand watered at 1 pint per plant every morning  jezza

[Lardman]

I have watered every day so clearly nothing to do with inconsistent watering . Obviously God hates me!

Certain varieties are also more prone to it than others, particularly the heirloom varieties.  I don't bother with beefsteak toms here anymore whatever I do because of my soil conditions they end up with BER.  I find growing an F1 safer, more forgiving, all be it not as tasty variety as a back up is a good plan.