One of the most confusing things about gardening is how to fertilize. There is A LOT of misinformation online about it and just as much marketing hype.
When we were starting we fell for most of it. We bought fish fertilizer, got our soil tested, and bought bags of bone meal. Lots of money poured down the ole shoot. The outhouse.
Robert Pavlis, and his blog Garden Myths, helped a lot to sort things out. We highly recommend a follow on his site, as well as his books.
If you don’t want to deep dive into the topic of fertilizer, here is the bottom line: Add some nitrogen during the growing season and/or just before, and keep adding organic matter (like mulch) to lighten up the soil.
The safest and easiest way to fertilize is with a good slow-release fertilizer like Ozmocote. Alternatively for general landscape use, a generic bagged fertilizer will work. Look for a ratio of 3-1-2, but 10-10-10 or similar is fine. The main thing is the nitrogen.
If you do want to go a little deeper on the topic, here is an excellent place to start:
https://www.gardenmyths.com/fertilizer-myths-save-money/
Whatever you do, don’t waste your money on Epsom salts or fish emulsion!