The timing for amending clay soil largely depends on the specific needs of your garden and climate conditions. Generally, it is best to amend clay soil during spring or fall when temperatures are moderate and there is adequate moisture in the ground. Working with wet clay soil is generally not recommended as it can compact easily and become clumpy when manipulated excessively. Before amending, ensure that the soil is slightly moist but not overly saturated from recent rainfall or irrigation. Amending clay soil at these times allows the additives to gradually integrate into the earth as they decompose over time.