you only need one per container because it will fill a container pretty quickly. It will just fill faster with more.

One mint seedling will easily fill each of those pots. And likely even larger ones! LOL! I wouldn't necessarily pull out the extras - they will assimilate or the more vigorous seedling in each will eventually overwhelm them.

FYI - 'garden' soil is not intended for use in containers - it is intended for use an amendment or to augment soil for inground plantings only. It tends to be of too fine a particle size and also quite dense, depending on the specific product and its ingredients. So by using this, you have greatly limited the ability of the containers to drain quickly and well. With mint, which is a moisture lover, this may not be all that much of an issue but with other plants it certainly could be. When you are dealing with pots and containers, you want potting mix, not any sort of garden soil.

And the stones at the bottom do nothing to improve drainage. In fact, they tend to impede fast drainage (you want uniform structure throughout the container for best drainage) and serve to elevate the perched water table that will ultimately result in this soil. If you were growing just about anything other than mint, I would urge you to repot in a properly structured potting/container soil. Without rocks :-))

Nil13, Good to know. BTW, what about the sideshoots that I started seeing at the base of the plant before I transplanted...do I leave them alone or snip them off?

Gardengal, lesson learned. We'll see how things work out this season. I typically use ProMix BX for my annual containers but figured I needed something more garden-like for mint.

leave them