I'm amending garden soil and need to add "coarse, sharp sand"—but I don't know what measurement corresponds to "coarse." The local nurseries and home improvement centers sell sand, but they don't describe it by grain size.
Can somebody please provide me with a brand and product name of the right kind of sand? Or a picture of some sand grains next to a ruler?
Can't help you with brands (from the UK) but sand particle sizes are approximately:-
Very coarse 1 -2 mm, coarse 0.5 -1 mm, medium 0.25 - 0.5 mm, fine 0.125 - 0.25 mm, and very fine 0.0625 - 0.125 mm.
Smaller than this are silts and clays, and larger gravels. I don't know if these are accepted definitions but they are good enough for our purposes. In the building trade "mortar" to lay bricks uses the finer fractions, fine concrete uses the coarser sizes. If I buy "sharp" sand locally here it will be mostly 0.5 - 1 mm with some small stones up to 3 or 4 mm, but that is just from a local "pit" which is river sand. Bagged sand from a builders merchant will be more "refined" and regular in size. How "sharp", that is gritty, will depend on local conditions. For your purposes you want the most gritty you can get to open up your soil and get air into it. The smallest gravels may also help you, and some organic content.
Are you amending clay loam soil? Do weeds and grass grow on it? If so, sand works great. If you have gray or blue dense subsoil clay, sand isn't going to work. You need to pile good topsoil on top. The beauty of sand is that it fixes your soil problem permanently, unlike organic matter which rots away.
I use whatever sand the trucking company can get. It doesn't look coarse to me. If it's not coarse, you will need to add more. You should start out with at least 25% sand by volume and till it in thoroughly. After it settles and gets rained on, you will know if you added enough. If the soil still hardens and cracks when it gets dry, you need more sand. So don't plant too quickly. The best way to buy sand is by the dump truck load. The little bags at the store are going to bankrupt you. It depends how much land you are trying to improve. The only practical way to amend a large area is with a small tractor with a bucket on the front and a big tiller on the back. You can rent them.
Once you turn your soil into loam or sandy loam, you will be amazed at the range of plants that can be grown without special care, especially alpines and bulbs. I won't even consider gardening in my clay soil until I have amended it. Even better, rake your amended soil into raised beds with walkways between them. Now you get better access for weeding, better drainage, and better aeration. Veggies really love raised beds. You can make fancy soil retainers with wood or masonry, but it's not necessary. You should also till in lots of organic matter while you are at it. If your soil is acidic, add some lime at the same time. If your soil is weak in phosphorus, add superphosphate at the same time.