Henna - does it have to grow out, or does it just fade away?

[FromGirders]

Commplete newbie to this whole hair-colouring thing, but I like the sound of the Lush hennas. BUT, I don't want to end up with scary dull brown roots. Have read different things on here - some people say that henna has to grow out, other people say it fades and you don't have any root issues.
Which is it, Oh Wise and Experienced MNers?

It will fade a lot but not completely. I used to use it all the time. If you want something that won't need retouching when your hair grows you need a semi permanent hair colour. They wash out after about 20/24 washes.

it will fade as it is semi, but what state is your hair in? is it coloured already, highlights? as these types of things will make a difference.

but if you really want the stuff to fade - get head and shoulders, it will stripe the colour out of your hair

It will fade a lot, but you'll still be left with a hint of colour. The red henna is pretty bright but the brown one is more natural.

Be careful about putting normal hair dye over henna as IIRC the chemicals open the hair shaft and push the henna further in. So you need to wait for all the henna to go or find a hairdresser who is able to do it without making a mess of your hair.

Have boring brown hair, shoulder length, never been highlighted or coloured before.
See here to make any suggestions for what to do with it .

Would you suit going lighter, just a tiny bit?

I'm not a huge fan of the henna stuff for longer hair as it can look a bit too solid and all one colour. The bright red is fab on shorter hair though.