Q: My son is building a large garden for a project. Because the soil in the area was packed clay when he began, he tilled it, added a dump truck load of compost and a truckload of old horse manure. He added the amendments 4-5 inches at a time, tilling after each addition. Despite all of his tilling, the amount of clay visible in the tilled mixture was low. The soil was then tested and corrected, but the flowers he then planted haven’t lived. Is it possible that his beds are too heavily amended? How do you fix over amended soil?
A: It’s hard to accomplish but soil can be over-amended. It all depends on how quickly the soil drains after a rain. Soil with lots of clay dries slowly, but so does soil with a high percentage of organic matter.
Good soil should be around 5% organic matter, with the rest being sand, clay and silt.
For more information on what you’ll need for healthy soil see my Soil ǃ