A question asked by most beginning bloggers.
Honestly, there is no right or wrong answer and there is no magic number of posts needed when a person has decided to launch into the world of blogging. In fact, there are a number of successful bloggers that started with only one post and kept blogging day after day. Many had no idea what they were doing nor had a longterm plan in mind.
Some people will plan out there posts by using a calendar and sticking with that plan. It really boils down to your own personality and how much energy you are willing to put into the project. Some will not launch their site until they have at least 10-20 well thought out articles. Some will write up to twenty or so and then begin stepping back to edit each one to create a tighter more readable post.
It does really help though to have a few written ahead of time so that when those moments of life get in the way by unforeseen circumstances there is something to fall back on. Then when time is available again write a couple more to replenish the stockpile. Sometimes it helps to just jot down ideas that might pop into your mind so that the article can be written at a later date.
Having only one post on your blog might discourage a person from coming back if they landed on your site through random searching. A good reason to start with a few articles in place that have been well researched and thought out so the potential reader finds your posts interesting.
Stockpiling articles is a lot of work. It takes discipline and time investing to get them done. But if you are a serious beginner and are willing to stick it out in this arena of blogs then putting in the effort day after day just might pay off in the long run. It certainly has for many.
The important thing is to begin. Start with five and notice how long it took to write those before launching your blog. Then if you are satisfied with the results then write five more. Drip the content onto your blog three times during the week and keep writing. Adding valuable content to a planned publishing list. It will help keep your stress level down by pre-planning and knowing that you have a few notes or articles in an archive to rely on later.
And as always check your intentions as to why you want to be a blogger.