The University of Minnesota Soil Lab will give you recommendations to make your lawn or garden more productive for just $17. Download the form at http://soiltest.cfans.umn.edu/files/2012/08/LawnGardenInfoSheet.doc and follow the instructions. You simply collect five trowels of soil from throughout your lawn or garden, mix it together and mail one pint of your sample to the University of Minnesota Soils Lab with the form and a check.
Two or three weeks later you will receive a summary of your soil texture, percent organic matter, pH, nutrients and suggested fertilization needs. With this information you are on your way to improving your garden soil.