Short hair - rebleach just the roots...or all?

Hi All,

I have very short hair and about 3 weeks ago I bleached it. Well my hairdresser bleached it once and I bleached again about 2 days later to get to a better colour. My hair, which is naturally a mousy brown, grows super fast and I already have about a centimetre of dark regrowth.
In the next couple of weeks I'll bleach again but what I'm trying to work out is whether I have to be really careful to just bleach the roots or whether it's ok to just bung the bleach through all of the hair.

I won't go to a hairdresser - I don't want to be paying every few weeks...and I'm not at all precious about my hair. (Hence why I had no concerns bleaching by myself with no idea what I was doing!)

I'm inclined to just do it all as it'll be tricky to do just the roots.....but common sense suggests my hair will be totally different shades of blonde if I do that.

Those of you with experience in this area - any thoughts/advice very welcome!!

 You def only want to apply the bleach to the roots ONLY. Over lapping on already bleached hair will cause it to break off. You should also apply a extra virgin coconut oil to all of your hair then bleach the roots to protect the virgin hair as well as the processed hair.