@tapla (mid-Michigan, USDA z5b-6a) might have an opinion on the qualities of good horticultural sand.

There are no precise "specifications" but it is typically processed from granite, quartz or sandstone, is pH neutral and has a rough/jagged shape and dimensions of 2-5mm. It can be used without any washing, as it contains no salts or impurities.

Builder's sand (aka coarse sand), builder's grit or horticultural grit can be used in its place without concern. They are not exactly the same but close enough to be equally serviceable for the same propose. They will require washing however.

I'm not sure you will easily find horticultural sand in bulk. I've never seen it sold that way. But there are several suppliers of washed construction or builder's sand in the area. Google is your friend :-))

@gardengal48 (PNW Z8/9) Thank you for calling out builder's sand at 2 to 5 mm, and that will give me more options. I would never buy anything without a sieve analysis as I know from hard experience that many products cheat and include fines.

We have a local supplier in the Bay Area that mixes soils and has a great coarse sand that they sell in bulk. The problem is they were willing to sell me a ton of coarse sand in a supersack in Winter, and now that we are in the busy season my order is too small and they don't want to process it. They insist I rent my own truck and just receive material unbagged. But even if I did that I have no easy way to store that much sand. And I don't want the sand getting organic contaminants while it waits to be used on small projects. So I am trying to identify a new vendor who can pack it in a supersack and palletize it for a freight forwarder to pickup up.

In the meantime, I just want to know the specifications so I can compare my target to the vendor's sieve analysis.

@gardengal48 (PNW Z8/9) I am finding a vendor with "#2 Olympia Sand". that looks visually like a washed sand with larger particles. Do you have any experience with that?

@gardengal48 (PNW Z8/9) By the way, 1/8 inch is about 3 mm, so your range of 2 to 5 mm is more like the inorganic components in the Gritty Mix. I think of coarse "sand" as being closer to 1/16 inch, which is around 1.5 mm. Most of what is being sold in local nurseries as horticultural sand looks to my eye to be between 0.5 and 1.5 mm. You would be surprised to see that most sieve analyses for builder's sand put 30% of the sand below 0.6 mm, which is why I always insist now on seeing a sieve analysis. The variations in fines across different sands that are given the same name can be enormous.

Lyngso is a well-known bulk garden material supplier in the North Bay Area and here is their sieve analysis for Olympia #2 sand:

https://store.lyngsogarden.com/inet/storefront/getpdf.php?recid=255

That has around 37% of the particles at or smaller than 0.6 mm.

If you say use Builder's Sand, go look at those sieve analyses and many are far worse. Home Depot carries Quikrete, and they have three grades of builder's sand. Their coarsest grade has the bulk of particle sizes from 0.6 to 0.7 mm.