Are your plants getting the nutrition they need?

1. Mass flow: Nutrients can enter roots with water as it flows in.
2. Root interception: As roots grow, they make physical contact with nutrients.
3. Diffusion: When the balance of ions (charged particles) in the roots and in the water in the soil is not equal, nutrients may flow in or out of the roots to balance the ion concentration.

Whichever way the nutrients get to your plant, you need good soil to "store" the nutrients for the plants. Certain types of clay and a substance called organic matter have an overall negative charge, while plant nutrients have a positive charge. Because of their opposite charges, the organic matter and clay can hold nutrients tightly enough that the nutrients won't wash away or become part of other chemical compounds unavailable to the plant. A high "cation exchange capacity" means soil can hold many cations (the nutrients!) for the plant.

Compost is a material that adds both nutrition for plants and lots of organic matter, which makes the soil more able to hold cations. Compost also structure and texture of soil, leading to better aeration and water flow. What materials you make compost out of ultimately determine the qualities it has a finished product. Contrast this with commercial fertilizer, which contains major nutrients (nitrogen, phosphorus, potassium) in rapidly available and more predictable amounts but does nothing to increase the soil's organic matter content or improve soil structure.

There are many places you can send a sample of your soil to be tested for nutrient status. This link from Cooperative Illinois Extension will take you to a list of labs: http://www.urbanext.uiuc.edu/soiltest/