Meditation and Mouth breathing Some meditation techniques use the nostrils as a point of concentration, others only mention that we should breathe via the nose.

Many people have problems with that and can only breath through their mouths. Is this a problem for meditation? How serious is it?
Here are some of the reasons that focusing on the breath is beneficial in meditation.
http://www.buddhamind.info/leftside/lifestyl/medi/breath.htm


  Using the breath: Why? Assuming you see the value in taking up a
  specific object for developing concentration, the breath has many
  things to recommend itself as the object of choice. 1 - it is
  portable. Every where you go you have it with you. No need to worry
  about forgetting your worry beads. 2 - it comes free with every body.
  No need to buy any special equipment. 3 - it is complete in and of
  itself. No need for any upgrades or add-ons. 4 - it is 100% natural -
  they don't come more organic than this. 5 - it is effortless. The body
  knows how to breathe without you needing to do anything, You just sit
  back and let it do all the work - while you just watch. 6 - it is a
  connection with a vital life force. 7- it is calming. There is a
  simple, natural rhythm the breath follows and following that leads one
  to peace.


All of these reasons but especially 4, 5, 6, and 7 indicate that breathing should be natural and unforced, effortless and done in a relaxed way. So the emphasis is not on trying to make breathing to happen in a certain way, but allowing it to happen natural. If the nose is blocked from mucous then the mouth is the only option.

But on the same page are many variations of how breath can be integrated in meditation:
http://www.buddhamind.info/leftside/lifestyl/medi/breath.htm
examples are counting, following, listening to noise. Observing and turning away.
Walking meditation can also use breathing in it.