Dotty,

Welcome to the forum! In general I would say you can wing it in September in Northern Ireland and Donegal. You always need reservations in Dublin. On weekends (especially if the weather is good) you may want to book a day or two ahead. You will probably want to travel with a list of your favorite B&Bs for each area you are considering staying. That way you can call ahead when you know your plans. B&Bs also will call and book your next B&B as well as give you recommendations. If you like the place you just stayed, chances are good they will recommend a comparable place for you.

There are far fewer B&Bs in No. Ireland than in the Republic.

Michele