Most of us aren't lucky enough to have the perfect soil waiting for us in the backyard, so we need to turn to soil amendments to bring it up to a good blend for most plants. 

The first thing to do is to figure out which type or types of soil you do have. This would not apply to raised beds unless you are using your native soil to fill them. The easiest way to do this is to get a set of samples from the area you are planning to use. Clear the area of any surface litter such as leaves, sticks, stones, etc. Dig a hole as deep as you are planning to use your beds, anywhere from 8 to 18 inches, 12 inches usually being plenty deep. 

Take a slice of the soil from the side of the hole and put it in a lidded jar about 3/4th full of distilled water (tap water could affect results if you plan on taking the pH; if you are not, tap water is fine). Make sure the lid is on tightly (unless you like mud baths!) and give the covered jar a good shake for about 2-3 minutes. Then find a place to set the jar that you will be able to reach easily and leave overnight.

The first soil content that will settle out is the sand (largest particles), so give it a few minutes and then use a washable marker to draw a line on the side to mark the level. After a few hours, the silt parts (medium particles) of your soil will have come to rest and you can mark its level on the side of the jar. After you have left the jar overnight, the clay particles (the smallest particles) should have settled down on the top of the sediment and you can mark this level. Check the picture below  and compare your soil sample to the drawing; it should give you a pretty good idea what type of soil you are dealing with.

picture courtesy of www.gardeners.com

What should be left in your jar is a bunch of cloudy, still slightly dirty looking water with maybe some floating pieces; those are the organic matter parts of your soil. If there are none, then you will most certainly need to add organic matter (mulches, compost, peat moss, etc) to your soil when you are amending it. 

Now that you know which soil is yours, there are options for each of these:

If you have clay soil, this type is usually packed solid with no room for air, and although it has a lot of nutrients, they are not very available to anything you plant in it. It tends to be waterlogged in the winter, and dry and cracked in summer. In order to build more air pockets in so the plants can breathe and improve the water retention, you must mix in organic matter, about 2-4 inches worth to start. You will most likely need to add at least 1 inch per year after that, or alternately you can grow green cover crops in the fall to turn into the soil for the winter. Your best bet is to have raised beds, especially if row planting is not for you.

If you have sandy soil, while it is more workable, the nutrients in the soil tend to wash away faster than other soils, often before plants can get them. This soil type would benefit from 3-5 inches of organic matter worked in the first year, and up to 2 inches in following years. Again, an alternative is to grow green cover crops in the fall and turn them under as compost. Mulching is also a good option for this type of soil to help hold in moisture and coolness.

If you have silty soil, this type needs the least amount of amending but still will benefit from it. Work in 1-2 inches of organic matter the first year, and either additional 1 inch the following years or grow cover crops. This type of soil would also benefit from raised beds as it is easily compacted.

A lot of places talk about soil Ph but unless you are growing a particularly picky plant, most vegetables and fruits will grow in well amended soil. Most herbs actually prefer poor or lightly amended soil!

If you find that you have done all your soil mixing and still some plants need more (as some of the heavy feeders will), there are some options that are natural and/or organic alternatives to the chemical versions often seen in your local stores: 

Two excellent multi-purpose fertilizers are the Earth Juice brand and E.B. Stone Organics Tomato and Vegetable fertilizers.