In my part of the world (Northeastern North America), there is a product widely sold as “black earth” that is very popular with gardeners. It is also very cheap. I’d like to say dirt cheap, but it is actually cheaper than “dirt” (topsoil). It is sold by the bagful in garden centers and even supermarkets where people load up their trunks with what they think is top-quality soil at rock-bottom prices. They’re very unlikely to be happy with the results.
Of course, this product isn’t black earth. Black earth (the real stuff) is a type of soil officially called chernozem. It is very rich in humus, chock full of NPK and ideal for growing most nutrient-dependant plants, including vegetables. Its usually found in what were originally low-lying, marshy areas, now mostly drained and being used for agriculture. If you really could get your hands on true black earth at a reasonable price, it would be wonderful: pretty much the ideal garden soil!
But the stuff sold as black earth is not chernozem, at least not in the eastern part of the continent (I’m sorry I can’t generalize: the term “black earth” can mean different things in different areas). In fact, it is not soil at all, but black peat, a very dark-coloured type of peat found at the bottom of sphagnum peat bogs, under the more widely used blonde peat (the top layer) used in most quality potting mixes and the somewhat decomposed brown peat moss (middle layer), a lesser quality peat used mostly in soil mixes for outdoor gardens.
Black peat is the lowest quality peat. It contains no fibre and, unlike other peats, compacts readily and doesn’t hold nutrients well. It needs to be amended with limestone for most garden uses, as its pH is much too low for most plants. It can be useful for amending clay soils (if you can get it to mix with clay: good luck with that!) and sandy soils, but its effects don’t last. Blond or brown peat are much better choices for this use.
But “black earth” (black peat) remains popular in the soil packaging industry… essentially as a colorant. No, packaging people will never say that, but essentially, that’s the case. They know gardeners associate a dark soil color with good quality soils, so… give the people what they want.
The problem is, you never know what you’re getting with a product labeled “black earth”. It can be nearly pure peat. One product I saw listed as ingredients: peat, humus, limestone, dolomite. Well, the peat itself is humus and dolomite is a type of limestone. So this product is essentially pure black peat with enough limestone added to bring the pH up to an acceptable level. You should never try growing plants in this. Yet the label says “earth” and many people assume that means they can use it directly from the bag for containers, vegetable gardens, etc. And that will lead to disaster. Very few plants will survive for long in black earth if it is just limed peat moss.
Other “black earth” products do contain topsoil and may be labeled “black earth soil” or “black earth topsoil”. They’re slightly better, but again, you’d be better off with regular topsoil, which is usually amended with higher quality brown peat.
In a nutshell, “black earth”, unless you are certain you are really getting true chernozem (and that may be possible in certain parts of the world) is at best a lower quality product, certainly not the quality product many gardeners think it is. At worst, it is strictly a soil amendment and not “earth” that you should try growing plants in. Personally, I avoid it like the plague.
But it will probably continue to be a big seller because people remain convinced dark soils are the best. But if black earth really were the best, why is it always the cheapest “soil” on the market? I know your mama told you this, but it’s worth reminding you from time to time: you get what you pay for!