If my wife and i are able to have a baby through iui, how long should we try to have a baby naturally for baby #2. my wife will probably be 34 for #2?

6 months: No definitive answer, but in that situation i would probably seek help after trying for 6 months post breast feeding.

Far to say: Generally, if you needed assistance getting pregnant with the first pregnancy, you probably will need assistance again with the second. Although, couples "get lucky" all the time, you should not count on that; and when you are ready for the second child, consider repeating what worked for you the first time. Hope this helps. Good luck.