Hi Ceeview,
Yarrow is aggressive so it can probably be planted in the soil. Or what's called direct sown. Here are the conditions you need for most forms of Yarrow.
Sow at 20ºC (68ºF). The
seeds germinate in less than two weeks. Sprinkle them over the soil and then lightly press them into the soil. They need light to germinate. Once they sprout grow them at 10ºC (50ºF) minimum. If you are going to direct sow this means waiting around two weeks after your last frost date for your areas before you
plant them.
If I remember yarrow are what are called fine
seeds, meaning very very small lol. Since my eyes aren't that good anymore I've found the best way to space them out is to pour the
seeds out on a piece of paper and then pressing my finger into them until a few stick and then scraping those off in one location and then going on to the next. But then I hate to thin
plants so I try to avoid it at all costs. Which is why I'm so careful at this stage.
The reason for the different names is that Achillea is the botanical or scientific name and yarrow is the common name. Almost all
plants have a botanical name but not all of them have common names. And then there are some
plants that have several common names or may even share one common name between several
plants. That's why when looking up information on a given
plant it is best to use the scientific name.
Hope some of this information is useful.