Median sand diameter
Turfgrass managers deal with sand all the time. A sand has particles of various sizes, and taken together those particles make up the particle size distribution, which I showed examples of in this post.
The particle size distribution charts can be difficult to read if you don’t look at them frequently. Actually, I’ll admit that even when I look at them frequently, I sometimes find them a bit confusing.
How about looking at a single number from the particle size distribution—the diameter of the average sand particle in the sample? There’s a term for this—the D50. The D50 is the diameter at which 50% of the mass of the sand particles will have a smaller diameter, and 50% of the sand will have a larger diameter. It’s the sieve size at which we could divide a sand sample in half. We could take a sand sample, put it on that sieve, and after shaking, half the sand would remain on the sieve, and half the sand would have passed through.
I made this chart to summarize the D50 values for 309 different putting green sands. These sands are from all over the world, and they represent rootzone materials, mostly, along with some topdressing sands.
I also calculated what the D50 would be for a sand right at the limit of the USGA recommendations on the fine side, and what the D50 would be for the very coarsest sand that would meet particle size recommendations.1
15% of the sands in my database (45 out of 302) have a D50 smaller than the USGA fine limit.
Although one could conceivably use a sand at the very coarse limit, I’ve never actually seen one even close. I suppose that a sand with particle sizes at the coarse limit would not meet the capillary porosity guidelines, so although the USGA recommendations have an allowance for coarser material, what actually gets used is almost always closer to the fine limit than to the coarse limit. ↩︎