For plants to grow they need a good foundation with all the building blocks to grow. Of course if all the plants needed the same things in the same amounts gardening would be the easiest thing in the world (of course everything would only grow in a single location too). However, plants have adapted to their natural habitat and as such we need to remake their natural habitat in our gardens for the plants to flourish.
Acidity of the Soil (pH)
pH – a measure for the amount of free Hydrogen ions. In the soil plants can use either the Hydrogen ions (H+) or the Hydroxide ions (OH-) to absorb nutrients from the soil. Plants that are use to near a lot of rain usually tend to like acidic soils, why drier plants usually prefer alkaline soils. The reason for this generalization is that when it rains that will usually wash away minerals (most minerals are alkaline) which results in acidic soils, lack of rain leaves those minerals in the soil leaving the soil more alkaline.
In the pacific northwest we find that with the Rockies to the east all that moisture hits the mountains and we get a lot of rain. Because of this most of the soil around here is acidic, which might be great for moss and blackberries, but detrimental to asparagus or mushrooms. So as you begin your garden take a pH measurement of the soil in a couple spots to get a good idea of what the average pH will be. Your local extension office will be able to determine the pH or you can get a pH meter.
Once you know your soil pH you can either raise the pH by adding agricultural lime (which also will add calcium and magnesium to the soil, some trace elements needed by plants) or lower the pH by adding ammonium sulphate (which also adds nitrogen to the soil). Be very careful to follow the directions on how much to add otherwise you will overshoot your goal and make it worse than before.
All plants need Nitrogen, Phosphorus, and Potassium (K) (Potash) along with other trace minerals to grow properly. In the northwest because of the rain our soils can lose these nutrients as they leach out of our gardens in head into the neighboring blackberries. So to prevent all those nutrients from leaching
As I said before the N-P-K nutrients are the main ones for plant growth however, if you plant in soil containing only these three elements, your plants will not do very well at all. There are actually 17 other elements that plants will use during their lifespan, these are Boron, Carbon, Oxygen, Sodium, Magnesium, Silicon, Sulfur, Chlorine, Calcium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Selenium and Molybdenum. Though it is possible to add these piece by piece (and setups using hydroponics will add these separately), the best is to use a well rounded compost mixture.
By well rounded I mean a compost that mixes many different types of source plant material (wood, greens, peels, etc.). When you purchase compost from the store take a look at the ingredients list, you’ll notice that they usually consist of a single type of material like wood byproducts, manures, leaves or something else. So if you are going store make sure to grab many different bags from different companies. If you are going to make your own compost set up a chicken coop and get some great manure along with all the scraps from the kitchen and the fall leaves or chipped branches and after a short time of about 3 months if rotated weekly you have great compost.
Soils will retain water to a point and then the rest will run off. That point needs to be customized for the plants so they do not drown but hold enough so that you are not constantly watering your plants. Generally to increase the soil retention loam-like substances are added, while to increase drainage sand-like substances are added.
In the northwest we usually find our soils to be not soil but solid clay which keeps the water on top of the ground, waterlogging the roots of the plants. To fix this problem it is recommended to add two parts compost to one part perlite/vermiculite to one part clay. The perlite/vermiculite improves drainage while the clay is great for water retention but the compost makes it easy to crumble.
So now you have your balanced, nutrient rich, moist dirt all ready for planting some great crops.