Lucia, I have a spreadsheet which I use for laying out vegetagles (i.e. a vegetable planting plan), for keeping notes on what worked well & what did not work well, for spacings between plants, notes on seeding planting dates etc. For knowing WHEN it is time to plant I've just referred to the state planting guide published by the Cooperative Extension Service. Actually, I used to do this moreso in the past because I now have the dates committed to memory. Having a notification algorithm in my spreadsheet would seemingly be more sophistication than what I would need. (If I did feel the need to have a reminder, I'd simply take the start planting dates out of my state planning guide and add these as reminders in the calendar program on my PC.)

I think such a spreadsheet is available at yougrowgirl.com.

I've considered using one, but a more primitive system works fine for me -- writing things down on a wall calendar. It stays right out in the main room where I'm less likely to forget it. When I'm planning the garden, I go through with a colorful pen and write my target dates for doing things, and later make notes of what I planted when. At the end of the season, I can stash it in my seed box.

Here is a link that might be useful: my website

Link to spreadsheet ... http://www.yougrowgirl.com/grow/seedstartingchart_lazy.php