I use typically potting mixture when I pot up smaller clematis. Plant the pot so that it is even with or slightly higher than the surrounding soil level. That way you can mulch around the pot and still have it be visible.

Most clematis are reliably hardy to zone 3 or 4. They should do fine in your garden buried in the ground or even above ground, especially if you get plenty of snow cover.

Feed them with a slow release fertilizer at the rate suggested by the directions on the fertilizer you purchase. The plants will let you know if they are not being supplied with enough nutrients by leaf color.