As Jane McGary's message points out, not all clay soils are equivalent. The one universal panacea is organic matter, the more the better. My NJ red clay, laced like a plum pudding with chunks of red shale, is slowly responding to compost, shredded leaves, shredded branches cadged from the county road department and used as a mulch (dusting of dried blood or cottonseed meal speeds their decay) and my favorite, llama beans. The last can be used intact, or shredded. be warned, the holes in a shredder/ grinder's screen are just that little bit bigger than the "beans" to result in spraying these little manure pellets all over the driveway with machine-gun rapidity. Organic matter is not like money in the bank. It continues to break down and needs constant replenishment. When you consider that an acre of deciduous woodland here in NJ drops a ton to a ton and a half of leaves and litter EVERY year, you gain an appreciation for what Mama Nature does in the recycling department. About gypsum - usual problem is that people dust a thin coating which is not sufficient. Gypsum, aka calcium sulphate, should be used at a rate of 5 pounds per 100 square feet in loamy soil, twice that rate of application if soil is heavy. Spread gypsum, dig in to thoroughly incorporate in top few inches, lastly thoroughly moisten the treated soil. Gypsum helps loosen heavy soils, most dramatically where high magnesium levels make matters worse. Judy in the Garden State with snow-so-deep (otherwise I could see my snowdrops)