Gypsum vs. Lime
Gypsum vs Lime
When it comes to lawn care and making sure your soil is healthy, you may hear the terms gypsum vs lime come up. Both are helpful amendments that can correct different nutrient levels that may harmful to your lawn and garden. But what are the differences? How do you know when to use gypsum, lime, or neither of them?
A good place to start is to know your soil and the problems you need to address. A soil test is always recommended to find out the nutrient levels in your yard. A key part of the soil test is measuring the pH of your soil. Soils with a pH below 7 are acidic while soils with a pH above 7 are alkaline. Both can affect the turf quality. Micronutrients tend to be less available in soils with high pH or alkaline soil while macronutrients tend to be less available in soils with low pH or acidic soils. Turf usually prefers a pH of around 6.5 – 7 on a scale of 0 to 14. It also helps to be aware of what else your soil is lacking or has an excess of based off of the soil test.
Educating our customers about pH, sulfur, calcium, lime & gypsum is a value offer we offer to our clients. A considerable amount of people believe that lime & gypsum can be interchanged for each other.
Lime
Lime, or calcium carbonate (CaCO3), is the naturally occurring mineral used to improve acidic soil. When the soil pH is less than 7, acidity exists as an accumulation of hydrogen (H), and aluminium (Al). Aluminium, which is toxic to turf growth, is soluble when the soil pH is less 5.5. When hydrogen accumulates on the outside of a soil particle, or exchange site, their presence is measured by a pH test.
When lime is applied to an acidic soil, the carbonate molecule (from lime) and hydrogen combine. The end products from this reaction are H2O (water) & CO2 (carbon dioxide). Calcium is now attached to the exchange site. Because the carbonate liberates the hydrogen, the soil pH will rise (become less acidic).
Gypsum
Gypsum, or calcium sulfate (CaSO4), is a naturally occurring mineral. It provides calcium & sulfur, both essential nutrients, but does not affect soil pH. Gypsum is a neutral salt (pH is ~6.7) and has a salt index, or osmotic potential, of 8. It typically has 20 to 22% calcium, and 16 to 18% sulfur. The sulfur is in a plant available, or sulfate (SO4) form. In addition to providing needed nutrients, the calcium in gypsum is soluble, even at a pH that is >7. This can be very helpful in improving soil tilth, reducing soil compaction, lowering sodium and improving aeration.
Gypsum is not the only way plants can get sulfur, but the sulfates in gypsum will not raise soil’s pH levels like elemental sulfur, the other commonly used additive. Elemental sulfur also has to steal calcium and oxygen from the soil in order to make its sulfur usable, something gypsum does not do.
The Takeaway
So, what’s the bottom line in the battle of gypsum vs lime? If your soil is acidic, gypsum won’t be able to help you. Lime can. Gypsum can add sulfur or take away sodium. Both can add calcium to the soil. Both are viable options depending on what your soil specifically needs, and it is important to know your lawn before jumping into the world of soil amendments. Always soil test!