I would say there are two main things: the health and fertility of the soil, and then there are conditions that encourage more worms to live there.
Usually the two things occur together, but do decide whether you MOST want to grow flowers and crops, or worms! (Are the worms just a means-to-an-end, or are they the goals in themselves?
If you are more interested in plants, then aim for rich, organic, well-aerated soil, and you'll get worms as a bonus. Consider the worms an INDICATOR of how healthy and organic your soil is.
- Add lots of compost! That is good for plants, and good for worms.
- Make sure the soil drains well enough to be well-aerated! That's good for both, too.
- Mulch! Protect worms and roots from heat, cold and dryness. Fewer weeds to pull are a bonus.
- Unless you really need to open up heavy clay, don't till or roto-till more than necessary. (It probably inconveniences the worms to be chopped up.) Always add compost and amendments when you DO turn the soil. Consider trying to imitate the action of a broadfork with a garden fork. Try to achieve "loft" and aeration by adding enough compost, other organic matter, and coarse soil amendments. You can always add compost or OM by sheet composting, trench composting or spot composting (spread it under the mulch, or dig a hole, dump and cover it.)
As for special worms, and special salts, if you want to grow worms in with your plants, I would think it better to seek to encourage "native" worms, or worms well-suited to your climate.
Think twice or three times before creating a nutrient imbalance (excess) because someone has advanced ideas about cultivating worms. Get a soil test before randomly adding soluble minerals! If your soil doesn't NEED something added, adding it anyway is BAD for the soil fertility!
If you focus too much on worms with special needs, won't the plants suffer? No one can serve two masters well.
I would experiment with worms in a vermicomposting heap or windrow - or, better, a tub or bin. You can get most of the benefit from worms by taking their left-over bedding with "worm casts" and spreading those in your beds.
Just be careful: if you follow some new idea for growing worms, make sure that their wastes don't poison YOUR soil. The person having great luck with his system might have very low levels of (for example) Manganese in his soil.
Say he adds lots of Manganese to his vermicomposting tub, and then spreads it over an acre of Manganese-deficient soil. Fine, good job.
Now suppose that you already have plenty of Manganese in your soil. You follow his worm-growing recipe. Say you spread the wastes from a BIG bin over a few small raised beds. Now those beds have a Manganese excess, and good luck recovering from it!
Everyone's situation is different.
