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I have approximately 1 year old soil and it is mud-like brown colour and texture with lots of composing worms if I dig even the surface, vs the new soil I bought that is black in colour and a bit granule-like texture with zero worm. Which one is healthier for plants? I’ve read that worm presents means healthy soil, but I have also read black soil is full of organic materials and pale brown isn’t very nutritious.

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    I'm not sure what "1 year old soil" means in this context; did you buy it last year and put it on the ground (or in a bed, etc)? It also depends very much on what kind of plants, and what you bought. Soil can be black for reasons other than organic materials. Did you buy compost, potting soil, or what? And for what are you using it? Putting plants in a pot has different requirements than putting the same plants directly in the ground. A lot more information is required to really answer this question. Jan 24 at 20:52

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The ideal soil is considered a "loam". That is approximately equal parts sand, silt and clay, which are different particle size fractions, and some organic matter (up to 10% or so). We are familiar with sand as a mixture of small grains composed of quartz, small but distinguishable by eye. Silt is a finer grade and can include other minerals. Clay is something else altogether, much finer, has a high water holding capacity and is rich in minerals, and can serve a kind of glue that holds the soil together (and sometimes expands and contracts with water content). The properties of clay depend on its chemical composition, so it's somewhat hard to generalize, but clay contains nutrients, while sand and silt don't hold much. Clay also retains nutrients effectively if you happen to fertilize, so you can load a clayey soil with nutrient in a way that you can't sand (which just allows nutrient-laden water to percolate right through).

If you judge your soils by appearance you can say roughly this: brownish soil is probably rich in clay and has all of the abovementioned properties. If it is too rich in clay it might be cloying and make it difficult for air and roots to penetrate and might get more readily waterlogged. The black soil is likely a compost and rich in carbon but probably poor in minerals, P and N, depending on origin and if it's not received a supplement (fertilizer). The black soil has the advantage of being looser, airy, and can improve the "tilth" or texture of clayey soil. So indeed, as the other answer suggests, mix them together. This is more likely to bring you close to an ideal loam.

Other properties such as pH etc are also important. Some of this information can be measured, other might be on the bag of the soil you purchased.

Oh yeah, with regard to worms, worms are (as the other answer mentioned) a sign that the soil is alive, which is very important. However worms and other soil organisms will crawl into your soil of their own accord unless you happen to have it in a pot, in which case you can always add a few.

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    Good answer but I would add that worms, like any animal, do a lot better when they have food to eat. That is why it's best to keep leaf litter in beds and mulch leaves into a lawn instead of collecting them.
    – JimmyJames
    Jan 24 at 17:58
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The microbiome of the soil is very important - having worms present are an indication of soil with an established microbiome as well as organic matter. That soil is probably good.

The black soil you purchased will not have much of a microbiome because its newly purchased. (Indeed it may have had the microbiome killed off in the process of killing the weeds). A Microbiome will re-establish itself once plants are planted.

You may want to consider mixing the 2 soils so the new soil can be "seeded" with the microbiome from the old soil.

I don't think anyone can answer which soil is better without studying it closely - and indeed different soil will be better for different plants.

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Agree with the above answers, except that I would not mix the two soils, as this would disturb the worm-rich soil and negatively affect its microbiome, for example by breaking up fungal hyphae, destroying worm burrows and small invertebrate habitats and potentially killing worms. Worm-rich indicates the soil is already in good nick. I would suggest spreading the black soil across as a type of mulch. If it's rich in organic material the worms will pull it down, and the mulch-like covering is beneficial in its own right.

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