I like what Laura was saying. Wood chips Wood Chips Wood chips. I have very heavy clay, and I've definitely seen huge improvements in 3 years where I laid down wood chips. The fungi will naturally grow in that environment. Radishes, turnips, comfrey, and even high biomass like oats will all help to grow. Comfrey has done so well in our heavy clay, sending tap root deep. Here in Colorado, its hard for it to grow wild, I would have more hesitation in your area.