Sowing calendars

I've come to the conclusion, after at least 40 years,  that I need to begin to be a little more organised.  In the spring I get all excited and sow anything and everything, fill up the patch at planting out and even if I wanted to successional sow, I haven't got the space.  So I thought a sowing calendar might be a reminder to be less enthusiastic in spring, leaving room for later sowing.  I run a desultory spreadsheet but the novelty wanes as the season progresses, I forget to look at my written garden book, so I thought I could run a second 'garden' calendar on my tablet completely separate from the existing humdrum daily household one, but I've yet to figure out how to have two distinct calendars.  The one I have syncs all together into one  display.  Next thought was an app with a reminder feature.  I'm still investigating than but I was after something simple.

I've heard PP talk about her sowing reminder, so my question is:  Does anyone have any bright ideas? What do you do to remind you about sowing at times other than spring?