Fiberous material in the soil will help it retain moisture and crack less, as will mulch. I'm confused about what you pictured as it doesn't look the same as the soil the plants are pictured in. Manure is a good fertilizer but doesn't do as much to loosen up high clay soil as fiberous material - Leaves, grass, pine needles, sawdust, even weeds. You can even throw your old excess seeds in the soil in early spring not caring if frost kills the growth because you're going to turn it under as a fiber addition to the soil.
Epsom salt can help but I was primarily referring to NPK nutrient sources. They look a little light on nitrogen particularly and clay soil impedes nitrogen delivery, water just sits and roots penetrate it slower. The miracle grow will give you that, though I would also consider adding some coffee grounds to add N as well as reducing the soil clay ratio.
