If a winter cover crop is grown to improve soil and prevent erosion, the ground will have to be tilled in the fall to prepare the soil for seed and again in spring to turn under the green manure. Spring plowing is better for sandy soils and those where shallow tilling is practiced. Generally, most gardens must be disked or rotary tilled in the spring to smooth the soil for planting. The correct soil pH is essential for optimum plant growth. Dolomitic limestone adds calcium and magnesium as it increases pH. Gypsum adds calcium and some sulfur but does not enhance the structure of Eastern clay soils as it does certain Western soils.
Agricultural sulfur is used to acidify alkaline soil.
The amount to add depends on the current and desired pH, which is one good reason to have garden soil checked periodically. Wood ashes can be used as a soil amendment. Wood ashes also raise soil pH with twice as much ash applied as limestone for the same effect. Ashes should not come into contact with germinating seedlings or plant roots as they may cause root burn. Other amendments are added specifically to improve soil nutrient levels.