Confused about companion planting

Hi all - daft question number 3.

I'm trying to be organic and have just watered my nematodes into the ground and scattered organic slug pellets in preparation for planting (finally got through the digging and weeding   ).

So while looking up companion planting it said to grow marigold and nasturtium (both of which are on windowsills at home, ready to go out) by potatoes.  But it said it works by getting rid of nematodes - yes the very nematodes I've just spent a fortune on!  Won't that cause the slugs to come back?

Oooh it's confooosin, this organic mallarky.