You’re supposed to do it once a season, but Consumer Reports says that 25% of owners never sharpen their lawnmower blades. I’m happy to report that I no longer fit in that lazy category, and found to my delight that it was easier than I thought.
First step was to pin the blade down in such a way that it wouldn’t harm me while taking it off the mower. The directions say use a 2x4 board, but I didn’t have one handy, and I found that a brick works just fine. In my case, a quick counter-clockwise turn of the main bolt was enough to remove the blade safely.
How to sharpen the blade: I suppose I could have found my own sharpener (I hear you can buy a small $4 blade sharepner that works with any power drill for example) but that was too much hassle. People say that local plant nurseries, or hardware stores will sharpen the blade (for free?) but after some calls to Lowes and Home Depot, I came up with nothing. Eventually I discovered that our local equipment rental place (Eastside Rental, in Bellevue) would do it while I wait. They charged an exorbitant $11, but it was worth it.
You should see how much better my lawn looks now!