How can I make my blond hair blonder?

I have dirty blond hair as well and I make it lighter every summer by getting some tea tree oil and rubbing it into my hair when you get up and be out in the sun as much as possible then wash your hair before you go to bed. Tea tree oil is so good for well everything form skin to hair. It makes you hair less frizzy, shiny, soft, and of course lighter. I use about 1/4 of a cup...If that seems like a lot you can also use a conditioner that has tea tree oil in it and use that instead but it takes a few more days. (By the way using plain tea tree oil takes about a week of doing that to make a difference by it is so worth it)