I'm not aiming to maximize yield, so I only add it once a year, to sort of "replenish" things. I also have a compost heap in which I compost grass clippings and autumn leaves, so I mix that in as well.

If I wanted to maximize yield, fertilization would have to be customized more (and I'd probably just use liquid fertilizer out of a watering can). What I have is adequate for my simple set up.

My parents were concerned about yields (because they sold part of the produce for extra income), so they fertilized several times a year, mostly either with manure or with guano (chicken poop), but they used granulated nitrogen fertilizer as well. Then again, they harvested three crops every year, and I only harvest one. It's not hot enough where I live to grow more than that.