Gypsum is gypsum…right? Wrong.
Gypsum is just gypsum and any will do, right? Wrong! Just like any product in the marketplace, there are high quality and low quality gypsum's and the adage of you get what you pay for is absolutely true.
Gypsum is a very misunderstood amendment; most people don’t understand the value. Before I talk about how the quality of gypsum can affect its effectiveness, let me give you a general overview of the material.
Gypsum comes in two different forms, both of which can be used in the turf industry. The first is calcium sulfate anhydrite and the second is calcium sulfate dihydrate. As you can read, both forms have both calcium and sulfur as part of the elemental make-up. The difference between the two, however, is directly tied to its effectiveness and that difference is water! The second form, calcium sulfate dehydrate, has 2 additional water molecules associated with the calcium sulfate crystal. It is these additional water molecules that make the elements of calcium and sulfur available to the plant within hours, opposed to days or weeks with the anhydrite form. For additional detailed information on the difference between the two forms, check out this video by Pace Turf.
Hopefully after watching the video you now understand that the ONLY gypsum you should use is the dihydrate form; now it is up to you to find the best form available.
By law, all gypsum bags must have a product analysis printed someplace on the bag. It will look something like this:
CaSO4-2H2O (calcium sulfate dihydrate)……#%
Derived from: calcium sulfate dihydrate
The most important line in the analysis is:
CaSO4-2H2O (calcium sulfate dihydrate)……#%.
This is the line that will show you the purity or the quality of the material. The closer that percentage is to 100%, the more effective and efficient the gypsum is for your particular application. As that percentage gets further away from 100% the more material you will need to apply to maximize the nutritional value of the gypsum.
Another major factor in your selection of gypsum had to do with the fineness of the particle that makes up the gypsum in the bag. So what does fineness mean? Fineness has to do with how small the raw material is crushed to and how much can pass through a mesh screen before it is bagged or pelletized then bagged.
Side note: there are various mesh screen sizes. For example, if the screen size is 10 mesh, that means there are 10 holes for every square inch. If the screen size is 200 mesh, it means there are 200 holes for every square inch. Remember, the higher the mesh size the smaller the particle has to be to pass through.
I added the side note is because particle size is directly related to the efficiency of gypsum. The smaller the gypsum becomes the more surface area it will cover. This is important because if you can cover more surface area with less product, you are maximizing the value of the application. The fineness can be found on the bag alongside the analysis.
There are a lot of options in the marketplace for gypsum and to the less educated user, it’s all the same. Now you know why that isn't true. Turn over the bag now that you know what to look for. Check the analysis and mesh factor to make an educated decision. Trust me, your soil will thank you for it and, hopefully, you’ll thank me too!