Mo,

I don't know exactly what they mean by black topsoil, and I wouldn't buy anything without looking at it first. We tried to buy a load of "sandy loam" once and what that company brought was pure sand. Well, not pure sand exactly. It was pure sand plus a billion weed seeds. So, I'd ask to be shown what the black topsoil looks like before I decided whether or not to buy it and I'd pick up a handful and feel it. Does it feel gritty like it has some sand in it? Can you see or smell any humus in it? (Probably not, though it would be nice.) Squeeze a handful of that black topsoil together in your hand and see if it holds together in a clump. That would indicate a somewhat high percentage of clay most of the time. Actually, if it had a little clay that might be a good thing because clay normally is high in nutrients and also helps sandier soils hold water.

The sandy loam you find unremarkable probably has quite a bit more sand than loam. If you add lots of organic matter to it, even just in the form of mulch that breaks down into compost over the years, it will slowly improve that sandy loam a lot. Pure sand is a whole lot harder to improve than sandy loam so I wouldn't want to get a whole load of really sandy, loam-free stuff unless I was wanting to xeriscape with sand-loving plants that need perfect drainage.

Is your native soil sand or sandy loam?

Finally, because it is on the west of the house, having clay in it actually would help up to a point as long as it isn't too much clay. So I am kinda hoping the black topsoil has some useful percentage of clay in it. If you put sand or sandy loam on the west side of the house, the plants you grow there will have to be really tough to handle fast-draining sand or sandy loam in combination with the western exposure's summer heat and intense sunlight. If it were me, I'd want a good sandy-clayey loam in that area because it would hold water longer than a sandy loam.

As much as I hate my dense red clay, plants grow better in it than they do in the narrow band of sandy soil that cuts across the property near the edge of the garden. I can add organic matter to the clay and turn it into a great growing medium even though it doesn't drain as well as I like, but with the band of sandy-silty soil, no matter how much organic matter I add to it, it never seems to improve nearly as much and it still drains too quickly.

If you click on the attacked link and go to the paragraph that starts with the words "Soil porosity", you'll find great definitions of sandy soil, loamy soil, etc. Reading those will tell you what you have a right to expect in a purchased soil product. However, soil companies call all sorts of stuff 'sandy loam' and often what they are selling has a very high sand content. Anybody can call just about anything they want 'topsoil' so you have to look at it first to see if it is good stuff or junk. A whole lot of junk gets sold to unsuspecting buyers.

Dawn

Here is a link that might be useful: Soil Primer

Thanks Dawn. After I posted at first, I thought I might should have mentioned that the bed will be raised and that might be a drainage/non-drainage factor.
The native soil we have is that old sticky black clay that goms up on your feet, and will get your pick-up stuck in the pasture because it is slicker than owl grease. It is very tiresome, but I have lived where the clay is red, and it certainly is a worse laundry problem than the black. There is also the occasional yellow streak in it, but mostly black. I guess that nothing is ideal, but you have helped me on this, ( not to mention countless other issues.
Thanks again. My brother in law has a place down on the river and it is so sandy that the sand burrs are terrible. I would hate to buy a truckload of sand burrs, although, they have a hard time surviving here.
mo