What's the best way to loosen up heavy clay soil? Many people try using sand especially since it's in such abundance in our area. Sand is usually not the answer through as drainage in soil depends on pore space. Sand has 40% large pore space and clay has very little. If you mix sand and clay, the clay particles reduce the number of pore spaces making the drainage worse, not better.
Organic matter in any form - peat, moss, saw dust, rotted leaves - anything organic will work. These break down and change the soil content to that the clay particles can lump together, creating pore space.
Organic matter in many forms are available at Christen Farm Nursery and the staff will be available to answer more soil questions or any other questions you may have.