I've been using castor oil on my scalp and ends for a few months now. I attempted a proper Castor Oil Challenge and failed miserably as I always forgot to record any definite results. That said, I have seen an improvement in the general quality and manageability of my hair. Not sure about growth though.
I decided to research some oils that may boost growth and found two that I liked the sound of... and they were available in Holland and Barrett so that kinda swung it!
Rosemary Oil - This is reported to be another great oil for hair growth. It's also used to maintain hair colour and ward off greys.
Lavender Oil - This is mainly because of the smell. However it's also meant to be good for general scalp health.
When you use essential oils like these you need to use a carrier oil as they can be too harsh. Olive oil and coconut oil work but I stuck to my trusty castor oil.
Here's my rough mix - this amount basically does my scalp and ends. I use Shea butter on the shaft of my hair as this mix is too heavy for the length of my hair.
3tbsp of castor oil
5 drops rosemary oil
3 drops of lavender oil
I pretty much made this up so I have no idea of I'm using the right amounts. I will attempts to monitor my hair a little better this time to see if I get any interesting results.
Lavender Oil 30 ml - Holland and Barrett £10.99 (Was half price when I bought it)
Rosemary Oil 10ml - Holland and Barrett £5.09