mints and lemon verbena

I managed to kill mint again. Only one of my three pots survived the winter- luckily it was my favorite the chocolate mint, but I wonder if it has to do with the container. The other two were in terra cotta pots, this one in plastic.

I cleaned it up a few days ago, pulling out dead strands of stem and root, and took a clipping of the largest bunch of foliage, to replant in the center.

This mountain mint was supposed to go into the shade garden- but I like its appearance so much I've been keeping it around on the deck.

The lemon verbena keeps getting a few leaves here and there, on the lower ends of stems, turn yellowish and dry up. It looks like the same affliction my stevia died of, and other plants. So I keep spraying it with soapy water (which did in a ton of whitefly that was attacking my clematis last week) in hopes to slow down or kill the pest outright. Whatever it is, too small or cryptic for me to see at all.