Is it necessary to add citric acid (lemon juice) when canning tomatoes?

@Jerri White, add the acid (lemon juice) in any case. It's not a lot: 1TB per pint, 2TB per quart. All the available literature instructs to do so for safe home canning. In my experience, I don't even taste the lemon juice and my tomatoes have never been tasted sour from the acid. You don't want to take the risk of getting sick or someone else getting sick.

yes, if your tomatoes are the low acid variety. The acidity is half of what keeps the bad stuff from growing in your canned tomatoes.