i used them last year. I had yogurt cups on bottom and the clear plastic cups that peaches or fruit cocktail comes in for the top. They fit together perfectly so I just duct taped them.

I've used yogurt cups for some of the annuals and veggies in the Spring. They are usually the last seeds I sow - the ones that require the warmest temps to germinate. I put them into a plastic box (actually an old refrigerator drawer) and place it up against the foundation on the south side of the house - the warmest spot in the Spring. Easier to water that way too - I can fill the box with water.

One drawback - the yogurt cups are small and dry out quickly - so last year I started using Cup-O-Noodles cups, instead of yogurt cups, which are a little bigger and hold more soil.

These containers have tomatoes, basil, parsley, and Yvonne's salvia -
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I used them a few years back when they still came with the clear plastic lids. Nice size & convenient, but I had quite a problem with them drying out, so you may have to water more often than with some other containers.