Every planting article you've ever read probably began with instructions on preparing the soil in your garden. You may have read these directions so many times you consider them as useful as the "do not remove" warning on a pillow tag. Though soil preparation recommendations may seem trivial, there are serious reasons why you should enrich your garden's dirt if you want to grow the most successful garden.
Drainage
Plants can be sensitive to the amount of water around their roots. Too much water and the roots can rot, while plants with too little water won't grow as well. The texture of your soil determines how much water it will hold. Sandy soil allows water to drain very quickly, requiring more frequent watering. Clay soil is thick and dense, and won't let water drain very well at all. Both extremes of soil can be cured by the addition of compost materials with the soil. Digging compost into clay can loosen it up and add air spaces for drainage, while compost will hold moisture that sand can't hold on to.
Feeding
While water may be the most important ingredient to your plant's growth, plants also need food to grow well and produce fruits and vegetables. Elements like nitrogen and phosphorus are crucial to plant growth. Each plant has different nutrient needs, but a good full-spectrum fertilizer or a solid layer of compost mixed in with the soil will add what the greater majority of your garden plants need.
Root Development
Whether you are growing vining plants like cucumbers or root crops like carrots, plants must have room for their roots to develop. If your soil is filled with weed roots, pieces of wood or rocks, your garden plants' roots won't have enough room to grow and thrive. Carrots and potatoes can grow twisted and misshapen, while plants above ground won't thrive if their root systems don't have room to expand. Remove all the obstructions in your garden before planting seeds to give you plants a smooth home in which to grow.
Weeds
Your soil has a finite amount of nutrients in it and you want them to enrich the plants you put there yourself. Weeds popping up in your garden steal nutrients away from your garden crops, leaving them not as healthy or vibrant. Prepare your soil ahead of time by pulling all the weeds in the space up by the roots. Dig down to make sure all the root balls have been removed, so they can't come back days or weeks later.