I agree with porkpal and Daniel.
Additionally, in my experience with our "lovely", nutrient-starved, Ohio clay soil, amending with peat moss loosens the clay to a loamy texture while retaining a good, even moisture level. And depending on the consistency of the clay, it could take *a lot* of peat!! By "loamy" I mean that the soil is light and workable while retaining a consistent level of moisture, so that it will compact in your hand, and hold its shape, without compacting into a near solid rock, but yet loosens up with ease. Think of the texture of typical garden soil that is sold in bags.
My raised beds begin by amending with peat and home made compost, if I have any, to loosen the clay. Then In the Fall, I add a thick layer of shredded leaves as mulch (watered down in hopes to keep *some* in place during high winds). In the Spring, any leaf mulch left in the garden is turned in to the soil along with compost, if I have any. The leaves aerate the soil nicely and add nutrients, as does compost.
Well drained soil allows the plants to stretch out their roots with relative ease, creating a good healthy root system. Even plants that thrive in heavy clay soil, such as daylilies, etc. perform that much better in well drained, loamy soil!
Hope this helps! Good luck with your gardening, my friend!
