My Roma tomatoes always get end rot on them ! How can I prevent this ?

Make sure they are well watered, and water at the base, not from the top. You can pick them when they are still green and let them ripen on the counter.

You can find calcium for blossom end rot in the garden center. This address says roma tomatoes are more susceptible to blossom end rot and spraying calcium on the blossom end of the tomatoes BEFORE any rot is present is the key to preventing it.

http://www.chicagonow.com/chicago-garden/2010/07/roma-tomatoes-disproportionately-affected-by-blossom-end-rot/

you have to be consistent with your watering

Blossom end rot is caused by a lack of calcium in the plant. There are bottles of spray you can use for that specifically. I went to one of my local garden centers, not a big box store to get it. You spray the liquid on the leaves and the tomatoes. It will not cure existing rot, just prevent it from forming on other tomatoes. It really does work! If your plant is in a pot, it will most likely get blossom end rot from all the watering it gets and no nutrients from the soil as it gets washed out so quick. Give it a try. If your tomato plants are healthy otherwise you are treating them well and shouldn't have to change anything else. The only other thing I would do is crush up egg shells real well and sprinkle them around the plant for a little longer term calcium. They also like a little coffee grounds, too.

Try adding Tomato Tone to the soil. This is usually caused by a lack of calcium. I add it to the holes when I am planting and then through out the summer. It has a lot of calcium and also plant food.

Add crushed egg shells to the soil around the tomatoes. The calcium from the egg shells prevents bloss end rot for us.