Tomato cracks (sometimes called “growth cracks”) are a problem associated with growing conditions. Dry weather that gives way to excessive watering or a rainy period can lead to cracking.When blossoms and fruit develop, tomatoes need more phosphorus and potassium. Excessive nitrogen can cause plants to grow too quickly, leading to cracking. If tomato plants dry out, water them just enough to keep them alive. Too much water at one time sets up conditions for tomato cracking. Once your plants have recovered from their dry spell, slowly re-establish a regular watering schedule.

I'm interested in this as I'm on my third ever and first serious attempt to grow toms. Now, TK..thank you for your advice, which is very helpful, and can I just draw your attention to the fact that the cracking in this case is on the stems and not the fruit. Is this the same problem as it would be with cracking fruit please?...just to clarify for me..thanks!

It applies to fruit and stems

I think you've hit upon it KT. I usually think of over zealous watering as the cause of splitting fruits which isn't the case yet. I didn't consider the stems splitting. I have been watering twice a day, whether the plants needed it or not. Now I will give it a little more thought. Many thanks, JTO.

Once ought to be enough i reckon. But then its so cold here, I rarely need to water mine every day!