All those are bone hardy. The first three could be wintersown. Horsetail doesn't actually have seeds. It is such an ancient plant it spreads by spores. You would need to find rhizomes.

However, I would urge caution, especially on the horsetail. It is well nigh ineradicable once in your garden. Basically that is a list of enormous, rampant weeds in a climate like mine so maybe a bit of research is necessary to see how they would behave in yours.

Thanks a lot florauk. So I could just plant some seeds whenever? Even if the ground is frozen? Im new to this so I have to ask pretty basic questions. Do I need to germ them first?

Yarrow, comfrey and nettles don't need any pre preparation. Rather than put them in the ground I would sow in a container - easier to protect from creatures and you will remember where they are. Look over into the Winter Sowing Forum and read their FAQs. It's a very easy method for hardy plants.

As I said above for horsetail you need to find rhizomes. But I would be really, really wary of planting that at all.