Soil and Additives

Do It Yourself.com: Fertilizer, Compost, and Soil
Series of projects, articles, and tips on fertilizing, composting, and nutrient management.
http://www.doityourself.com/scat/fertilizercompostsoi

Gardening Information: Soil
Collection of articles from Oregon State University on various aspects of soil: use of amendments and cover crops, temperature, acidity, moisture, and testing.
http://extension.oregonstate.edu/news/category_search.php?searchCat=soil

Improving Soil
Oregon horticulturalist offers information on soil components, pH, testing methods, and nutrients, and means of improving it by using amendments and improving drainage and aeration.
http://www.rodsgarden.50megs.com/improvingsoil.htm

The Schundler Company
Collection of articles and resources about the horticultural uses of perlite and vermiculite.
http://www.schundler.com/hort.htm

Soil Testing is an Excellent Investment for Garden Plants and Commercial Crops, HYG-1132-99
Ohio State University fact sheet covers the benefits of testing garden soil and provides recommendations for testing frequency, collecting a sample, and submitting to a testing lab.
http://ohioline.osu.edu/hyg-fact/1000/1132.html

Vermiculite.com
One-page site giving suggestions on where to purchase vermiculite in the United States, along with some uses and properties of vermiculite.
http://www.vermiculite.com