The lettuce hasn't grown as much this week as I would have expected. Could be it's colder than it usually is outside in the spring, even though 50-55 isn't too cold for them. They are also pretty crowded, and as soon as I took this picture I had my first microgreens, and thinned the plants. I'm afraid I saw a suspicious little critter that looked like a fruit fly around the lettuce, and I probably have fungus gnats.
The larva of Fungus gnats damage the roots and indoor plants grow slower because of it. Outside the fluctuations in soil moisture keep them from being a problem, even though they're around. Since I planted my lettuce in potting soil that's been outside for the summer it won't be a surprise if I have them, and I'd better start dealing with them, since I'll start all my seeds in this potting soil. Even though these are young plants, I'll let the soil dry out as much as possible before I water the lettuce again. I've only watered it once since I planted them, since the potting soil had plenty of moisture in such a deep pot for so little plant material. I'll also put a yellow sticky trap nearby and see if I catch any. This is a card covered with a sticky substance, and a great many insect pests are attracted to the color. It's mostly a monitoring device; it will let me know how many I have. But if the numbers are small and it kills the adults then I won't have to worry about them laying eggs, either, and the yellow sticky trap will also serve as a control.
Posted below is last week's picture, so you can see the growth in a week: