A diary helps you keep track of what worked for you and what didn't.
If you are like me you will forget what was planted
where and when. What variety of vegetable is important
because what grows well in one place may not grow well
in your garden or on your plot.
A great sentiment but when you are busy it is too easy to think 'I'll
jot that down tomorrow' and, of course, tomorrow
never comes....
There used to be a great book called The Vegetable Jotter which now
seems to have turned into The
Vegetable & Herb Expert - a great guide, also available in a pocket
version,
but lacking the space to note planting dates, results
etc.
You can find some background information on the site here