We have red clay to China. I have read where people say to add/mix stuff into your soil & that is what this article recommends. We DO NOT recommend that because we lost many trees, shrubs, and bulbs from mixing amendments into the soil. What worked for us was to plant white clover (green manure) & to put lots & lots of compost & mulch on the top of the soil. We also learned to plant high. Be careful about mixing into the soil. You create a clay bowl at the bottom that holds lots of water when it rains. We also do trench composting & you can find how to do that on Google. BTW, making your soil better is a long, long process. We have been at it for 12 years.