There are many materials one can use to provide this or that nutrient, but regardless of whether you want to use Miracle Grow or organics good management of soil fertility demands you know what your soil has in it. Get a soil test and you will likely find your soil has too much of one thing, a good amount of most things and not enough of something else.

Even with organics you can over fertilize your soil so please start with a soil test and tell us what it says and we can help you find organic materials to fill whatever it needs.

A good reliable soil test is the first part of knowing what, if anything, your soil may need as justaguy2 has stated. Contact your local office of the University of Maine USDA Cooperative Extension Service to inquire how to do this. You can also dig in with these simple soil tests to learn more about your soil,
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
and can lead you to making the soil you have into a good healthy soil that will grow strong and healthy plants.

Here is a link that might be useful: UM CES

Dr. earth has a good selection of organic fertlizers, single-ingredient as well as multi-ingredient. Organic fertilizers, as well as non-organic fertilizers list their nutrient content on the label. Another good source of organic matter that provides some fertilization and is excellent for building soil structure is manure.

John

Matthew, do you compost? If not, then get started :-).