Growing Lettuce in a Fish Tank

Some Computer Science students at Colgate have asked me if I plan to start blogging again, so here is my attempt to get back on the blogging bandwagon. (We’ll see how long it lasts once the baby arrives in September.) This post is actually about a project I did with H back in February: planting lettuce in a fish tank turned greenhouse.

We’ve used the fish tank as an indoor greenhouse several years in a row. There are several motivations for using a fish tank as an indoor greenhouse: (1) fish tanks are cheap, (2) they allow in plenty of light, (3) they catch extra water when I inevitably overwater the plants, and (4) most importantly, it keeps our two cats from eating our plants.

Fish tank

We’ve collected a large stash of plastic jars that we re-purposed as pots.

Cashew jars repurposed as pots

I drilled eight holes in the bottom of each jar to allow water to drain out. I don’t recall how large of a drill bit I used (perhaps 1/8″), but in retrospect I should have drilled larger holes (e.g., 1/4″). The pots didn’t drain very well with the smaller holes, which meant that some of the lettuce got moldy, and I had to compost it.

Cashew jar with holes

H helped me fill the pots with potting soil. He made less of a mess than I expected. 🙂 Then we planted two types of lettuce seeds: Mesclun Sweet Salad Mix and Burpee Bibb Lettuce. We also planted some mixed herb seeds we had lying around from last year.

H fills pots with dirt

We used some plastic spoons we had lying around to label each pot. H used the spoons to help mix the seeds in the dirt—a step which is entirely optional and probably not recommended.

Pots labeled with spoons

I’ve learned from prior years that the plants grow better if the light from the grow lights is more concentrated. Consequently, I lined the inside of the fish tank with aluminum foil on three sides. I used a few pieces of masking tape to stick each piece to the fish tank. I left one side un-foiled to allow natural light from the window to reach the plants and make it easy for H to look at the plants as they grew.

Fish tank with foil Upstate New York doesn’t get much sun in late winter (and neither did south-central Wisconsin), so I purchased two TaoTronics 24w Led Grow light Bulbs a few years ago. I also purchased two clamp lights (and removed the clamps). I mounted the clamp lights on a wood frame I built to sit on top of the fish tank. The frame allows the lights to b 12-18″ from the plants: far enough away from the plants to avoid “burning” the leaves, but also close enough to ensure the light is concentrated. The frame also keeps our cats from getting to the plants.

Grow lights and frame

Here’s what it looks like with the lights on.

Greenhouse with lights on

And here’s what it looked like outside while we were doing this project: it was actively snowing.

Snow while planting

We don’t have any pictures of the full grown lettuce, but as I mentioned above, the bibb lettuce got moldy and had to be composted. The rest of the lettuce was edible, but a bit scraggly—probably a result of poor drainage. The herbs didn’t grow well—probably due to poor drainage again and the seeds being a year old. Next year, I plan to skip the bibb lettuce and just do the mesclun. I may also branch out and try to start some tomato, cucumber, and zucchini plants that we can transplant outside once it’s warm enough.