A garden journal is your own personal diary of what happened in your garden. It will be a daily record of your achievements from year to year and of the changes you've made to your garden. It's also a great way to record how much you've learned from the very first time you planted a garden to now.
What's great about a journal is that when you get done with recording a gardening season, your journal becomes your own personal book filled with facts and information about what went on in your garden and how you did things. What great fun it will be to look back at these "books" that you wrote and have great hours re-living your experiences in the art of gardening.
Your journal can be as plain or fancy as you like. What's important is that you keep one. Use a 3-ring notebook, school notebook, or one of the special books with blank pages that lets you keep track of all the details.
Your journal should be a daily record of what you did in the garden, how you did it, what the weather was like, your successes and failures, what grew well, what didn't, varieties you used and how they did, exciting things you saw or did and any other personal thoughts you have about your garden.
Also include drawings and pictures of your garden and you in your garden. You may even want to included pressed flowers or leaves. Your garden journal will become a snapshot of a particular day and all those days put together give you a picture of your exciting garden year.