I noticed a lot of comments on the LA Times’ blog where people were confused about tomato pruning. Here’s the comment I posted there to help clarify:
Yes! It’s hard to know which is a sucker and which is a lateral until you’ve been into the tomato plants! But here’s the main rule: there is only one leader (generally) and all other side shoots are suckers. They grow right above almost every leaflet. Don’t remove the leaflet; just remove the sucker growing out of its crotch. A lateral IS a sucker that you decided to keep.
The general guideline is: retain the leader and the first sucker that shows up above the first fruiting cluster on the main leader. Or wait until you see a sucker (above the first fruiting cluster) that is a hefty size and keep JUST THAT SUCKER. I cut off all but one sucker on some of my plants.
Having said that, it’s best to keep several laterals (or “suckers”) on the following varieties: Brandywine, most cherry tomatoes, grape and pear tomatoes. But don’t go crazy; only keep maybe 3 or 4 suckers on the plant and prune all the rest.
Then there are varieties which send out new suckers RIGHT OFF THE END OF A FRUITING CLUSTER! How dare they! So cut the frilly end off that fruiting cluster!
Some varieties (like Champion) send out tons of suckers at their base, right near the ground. No matter which tomato variety it is CUT ALL THE SUCKERS THAT COME UP BELOW THE FIRST FRUIT CLUSTER, AT THE BOTTOM, leaving only the leader! Otherwise, you may never see a decent tomato on that plant.
Does this help?