I began keeping a garden journal several years ago, It was just a regular journal with blank pages. I kept a record of my purchases and receipts. I noted rain dates and frost dates. I refer back to it from time to time. I often forget about plants that have gone dormant, until in the spring when I get out digging around and my spade strikes a bulb. Then I remember. A journal helps me with that as well.
I found a wonderful journal from Lee Valley Tools, and my mother surprised me with it for my birthday! ( I just haven't had time to post about it. shhh) , Any howsey, it is a beautifully crafted 10 yr journal with 541 pages. It has no pre printed years, so you can begin it at any time. I was so thrilled with it, I just had to share.