Jonathan Green's Mag-I-Cal Plus for Lawns in Alkaline & Hard Soil contains sulfur and calcium sulfate dihydrate which lowers soil pH, is important to cell development and is vital to many grass plant functions. Poor soil that is hard and compacted is often the problem when it comes to growing a great lawn. When soil is too alkaline and compacted, air, water and nutrients cannot get down to the roots and the grass will not grow properly. Lawns thrive in slightly acidic to neutral soil with pH levels between 6.2 and 7.0. In soils with pH readings of 7.0 to 9.5, weeds thrive and the grass becomes light green and spindly. Additionally, Mag-I-Cal Plus helps to break up clay and compacted soils. This improves root penetration and promotes growth by increasing biological activity and releasing nutrients trapped in the soil.