I know it sounds like hairdressers are just having a moan, or trying to make more money, but I'm here to tell you why it really really matters how long you leave between your bleached blonde root appointments.
You've got your lovely new bleached hair, you promise to book in 6 weeks later, but life gets busy, your roots don't look too bad, so you leave it a few more, and suddenly its 11 weeks later. You book in for bleached roots and a trim and leave your hair appointment disappointed that your hair now has a band of darker blonde. Darn your stupid hairdresser who fucked up your hair.....right?
There is a science behind this frustration (both from you and your hairstylist!)....so hold tight.
When your hair is growing from your scalp, its newly formed and delightful. It responds to bleach really well, and tends to lift up creamy and clean. As the hair shaft ages (that infamous 6-8 week growth) the hair cuticle stands to harden up to the world. It now won't lift as well, and will get stuck in that stubborn darker/warmer zone.
In addition to this, your scalp gives off heat, and when you have a chemical process happening on your hair, the hair closer to your scalp reacts differently to hair that is further away. This means that a simple solo application of bleach won't give an even result, as the hair closer to the head will be warm (which speeds up the process).
This means that your hair won't process evenly, and you'll end up with that dreaded band.
If you come to the salon with a long root, a simple bleach root process won't give you the result you want. You will either need to have it all platinum card foiled, or double processed where the older hair (further away from your scalp) is processed separately from the newer root hair. These services obviously cost more.
If you want to have clean bleached hair, you need to stick to the upkeep. Soz.