How do I subscribe to a grow diary?

Well, I have been looking through the FAQs but have been unable to see how to do this. I am sure it is a simple button that I have been staring at for the last 2 days, but I have finally given up. Time to ask for help.

Just post on the thread to subscribe thats how i've always did it anyway!

see where it says thread tools.
click it.
it will be the last option.

*found this is in another post, thought I would post it if anyone looks here