Without seeing a recipe this is a total guess but it sounds as if you are underproofing the dough resulting in too much oven spring which in turn is leaving a split/ugly ridge.

Jeff

I just think you need to work on your shaping.  Of course if your seams are not sealed properly you will get tears in the weak areas.  Even with slashing weak seams will be a weaker area than your slashes and of course your oven spring is going to go for the path of least resistance.

The rise after you shape the loaves, before they go into the oven, that is called proofing.  If you don't let it rise long enough and put it in the oven too soon, it is underproofed.  If you wait too long and put it in the oven after you should have, it is overproofed.  Recipes will tell you a time to let the dough proof, but because the conditions where you bake (especially temperature) will never be the same, you need to learn to 'read' your dough and know when it is ready to go in.  Recipes will sometimes say "fully proofed' or "3/4 proof" when it should go into the oven. 

Jeff is suggesting you try letting that rise be longer,

I'm getting pretty better at judging when my dough is fully proofed.   But I feel like you have to have made the dough at least once before to ge able to estimate when it would be fully proofed and then figure back to guestimate when a loaf is at 3/4 proof for recipes when it is to go into the oven at that point.

Sometimes I get that dreaded side splitting as well. I dont think it has anything to do with how I shape the loves. Sometimes it is not that severe and other times it is. I am glad that I am not the only one that has this problem.

Maybe not enough of a "skin tension"

The only time I tend to get splits is when the loaf isn't pulled tight enough (for lack of a better term). For example, when shaping boules, they should be stretched until they have almost a skin to the outsides. I get side splits when I get lazy and just get them to round, but not firmed up

I've been baking bread for 29 years and had that happen frequently...I read in a bread cookbook (don't have a clue the name of it) several years ago that if the bread hasn't risen enough in the bread pan, and it is put into the oven, it will split.  The reason is that the heat from the oven makes the bread finish rising...and it does it quickly because of the heat...so if it is too under risen when it is put into the oven, the quick heated rising makes it split along the side.  I'm sorry if this isn't clear...but I do know that when I started letting my bread rise longer than I thought it should, it quit splitting along the side.  I hope you find a solution.

A couple things that will help with splitting

1.  Make sure the bread is adequately proofed (the rise after you shape it). If you poke it, the indentation should fill slowly and incompletely. 

2.  Make sure you are getting a good tight seam when you shape it. I pull my boules really tight, and gather up the seam in my hand and give about a 90 degree twist before putting it on the shett for the final rise. 

3. Make sure you slash the top deep enough. Unless you are doing something really fragile (brioche, ciabatta), a good 3/4 inche is probably advised. 

In my earlier days of baking, this used to happen to me all the time.  I found out through experience that I wasn't letting the dough rise long enough ...You should go ahead and have fun by letting a loaf rise way too long until it falls, poking it now and then along the way so you get familiar with what it feels like at all different stages clear up to and including the point of failure.  You'll never have your splitting problem again.  You can also get splitting if the dough is too dry (too much flour or not enough liquid) or if it was not kneaded thoroughly enough (or the gluten developed well enough in some other way ...time and french folds for example).  Just my 2-bits...

Brian

In baking term its called "break and Shred". In this case add more water in the dough will solve the problem. The more you add water the less split on the side wall or stay same water amount with less mixing time.

I agree with the underproofing comments, however, I have also found that uneven oven heat is a factor as well as size of bread pan.  If you fill it too full,  (pan size too small) then it will rise above the pan when proofing, thus looking like it has proofed enough (but it really hasn't because of the volume in the pan) and so you basically end up with the underproofed scenerio again.  Just my thoughts.