Commercial fertilizer can be very dangerous to your health, in spite of what a lot of folks will tell you.
There are numerous safer ways to fertilize your plants. Below is a list of some of the best fertilizer you can use.
Coffee or tea grounds. These are some of the best fertilizers that you can get, at very low cost. Most folks drink either coffee or tea, so when your done, use the grounds to fertilize your plants. An added benefit is that earthworms love these also, and spreading them in your garden will help attract them, and keep them in the garden.
Crushed eggshells. Crushed Eggshells put calcium back into the soil, which is very important for vegetables such as tomato's. When you plant your tomato's, make sure to dump a handful of crushed eggshells into the hole before planting. You can also scatter them on top of the soil, which helps feed your friendly earthworms again, and, as an added benefit, it helps get rid of snails.
Compost. Many people don't have room for a compost pile in their yard. No worries. You can take a barrel and make one, or, you can buy small compost barrels from various companies. You can also take a 5 gallon bucket, with a lid and use it for composting. When you put kitchen scraps in the bucket, make sure to put some leaves, grass clippings, etc... in it also, or you'll just have a slimy mess for several weeks. Do NOT put citrus fruit in the compost, the acid will kill your earthworms and other beneficial critters that help break down the compost.
Earthworm poop. Another excellent compost. If you have a way to raise earthworms, you can make earthworm tea, and use the earthworm poop, called castings in your garden and houseplants.
I will be adding other fertilizing options later, as I think of them.