After weeks and weeks of hot, dry weather, the topsoil and mulch in the garden becomes baked to a crust. This is why we often see summer rains running atop and off the garden. It is a good practice to cultivate the top few inches of any open areas in the summer garden to lesson runoff and aid in the absorption of the much needed rain.
I find the long-handled four-pronged cultivator or the u-shaped hula hoe to be the perfect tools for this type of work. There are many enriching mulches available now (those with added organic matter, seaweed, etc.) that can be added to the garden when the work is done to make this project a most satisfying twofer!