Preparing food for plants is more chemistry than cooking, however. I had to refresh my knowledge of NPK (nitrogen-phosphorous-potassium) and try to figure out how much of each thing was needed. Apparently you should test the pH of your soil before fertilizing. I say apparently because I didn't bother - I was just happy I remembered that they need food at all.
This is the most common organic fertilizer recipe on the web.
4 parts seed meal or fish meal
1 part dolomite lime
1 part rock phosphate or 1/2 part bone meal
1 part kelp meal
My homemade fertilizer
I accidentally bought both fish and alfalfa meal (which apparently can be substituted for each other), and it also turns out that kelp meal is ridiculously expensive (like, feed my plants or feed my family kind of expensive). So, I had to come up with my own recipe. Finding a kelp meal substitute was hard; I finally looked up the NPK of both and worked from that. Kelp meal is roughly 0-0-10 while potash is 0-0-50, hence the 1/5 portion. The potash was also $12.99 for a big box.
2 parts fish meal
2 parts alfalfa meal
1 part dolomite lime
1/2 part bone meal
1/5 part sulphate of potash
Things you should know
- Mix this outside. The dust that comes off the fish and alfalfa meal is crazy, so don't lean directly over it while mixing. Also, the fish meal has a horrendous smell, like a cross between cheap cat food and pee.
- Keep the mix off your plants, stems included. Otherwise, they'll get burnt.
- Use sparingly. While I couldn't find any firm direction on this, it looks like 1/2 cup dug into the soil around potted plants is good.
- Dig it into the soil before planting anything. Since I didn't plan ahead, I'm going to try hoeing around the plants in the garden, sprinkling on some fertlizer, and then raking it over.
- I'm not sure that I'd do this again. While it's nice to know what's in your fertilizer, it's not exactly cheap. I'm currently researching less expensive options, like using coffee grounds, egg shells, banana peels and other things I would normally compost anyway.