*With the help of my dear father I figured out it is indeed a tomato plant. The conversation went a little like this:
Me: Dad, how do I know what I planted is a tomato plant and not purple coneflower?
Dad: Well, tomato plants have a very distinctive smell. Crush a leaf between your fingers and see how it smells.
Me: What do tomato leaves smell like?
Dad: [pause] Well, I guess they smell like tomato plants.
This hunch was later confirmed via an emailed photograph of the plant in question. But just in case you ever mix up your seedlings, the tomato plant is the one that smells like a tomato plant.
The lettuces are doing splendidly (they like cool, wet weather), so well that they are getting pretty crowded in their bucket. So I decided to make a second lettuce planter.
Hat tip to Ms. Jess for helping me realize that the extra under-the-bed storage drawer that has had no place in my apartment for at least two moves now would make an excellent shallow planter! Worried that its translucent plastic would cook the roots of whatever I planted, I lined it with black garbage bag (cut one down the side seams and it fits perfectly) and pinned it with clothespins. Inside the garbage bag, I lined the bottom with about 1.5" of styrofoam peanuts. This helps with 1) drainage, or in this case, giving extra water a place to sit that won't water log the roots and 2) keeping the weight of the planter manageable. As an afterthought, I decided to drill a few holes in the very bottom corners of the bin and managed to catch the garbage bag on the drill bit with almost every hole. So, the garbage bags have some holes, but now so does the bin. Breathe, dirt. Breathe! It's not the prettiest solution, but it is doing its job. I planted mesclun mix leaf lettuce around its perimeter and they are sprouting already.
Warning: when using a shallow container, be sure that you are raising plants that are shallow-rooted. 6" is not a lot of dirt! These drawers would make a decent seedling bed that you could transfer plants out of later.
Lastly, I did a little deck clean-up and reorganization today. When we moved into this apartment, we inherited, among other things, a weird wood table/shelving thing that has been sitting on our front balcony doing absolutely nothing. Today I moved it out back to hopefully change up the planter levels (prior to this everything was sitting on the ground looking rather un-landscaped).
From left to right, top: oregano, catnip, chives, pretty flowers; bottom: more flowers, sad eggplants, lonely tomato, big bucket of dirt, lettucesIt looks much nicer now, really. And it will look even better when things warm up more.