When it comes to improving clay soil for gardening, there are a few key additives that can make a significant difference. One of the most important amendments is organic matter, such as compost or well-rotted manure. Adding these materials helps to improve drainage and aeration, as they break up the heavy texture of clay soil. Additionally, incorporating sand or perlite can enhance drainage further and prevent compaction. It's worth noting that adding too much sand can cause the soil to become overly sandy, so it's important to find the right balance. Lastly, applying gypsum can also be beneficial in breaking down clay particles and improving the overall structure of the soil.