Lettuce is a vegetable that most people at on a daily basis, so it is always a necessity in the household. It is also an ideal addition to your greenhouse garden for that same reason. Lettuce can be very tempermental, wanting to thrive in cooler temperatures. It is a great vegetable to grow in a greenhouse since you can control the temperature.
Layer a seed tray with the soil until it is about 3/4 inch within the top rim.
Sprinkle the lettuce seeds onto the soil, making sure not to layer them on top of one another. Then cover the seeds in a thin layer of soil, patting down lightly.
Mist the seed tray with a spray bottle filled with water to make the soil moist. Wrap plastic wrap over the seed tray to trap the moisture so the seeds won't dry out, then place the tray in a place where there is air circulation.
Keep the greenhouse temperature from 50 to 60 degrees Fahrenheit to ensure that the lettuce seeds will germinate. Make sure to keep the seed tray moist with the spray bottle when necessary.
Discard the plastic wrap when the lettuce seedlings grow to about an inch tall. Thin them out if there are crowded areas, so there is about 1 inch in between each seedling.
Transplant the seedlings when they have about 2 to 3 leaves each, usually about five weeks after they sprout. Use one gallon containers for the transplanting. Prepare the soil for them by mixing a small amount of fertilizer with the soil, then filling the containers to the top. Use your finger to poke a small hole that the seedlings roots will fit in, then fill the hole carefully with water.
Remove the seedling from the root tray by gently tugging upwards until the roots come out. Carefully put the seedling into the hole, making sure the roots are fully inserted into the hole. Pat soil around the stem of the seedling. Repeat this process with all the seedlings.
Continue watering the transplanted seedlings with the misting water to maintain moist soil.
Harvest the lettuce once it has fully matured, which is usually around two months after you transplanted the plants. Each type of lettuce requires a different type of harvesting. For instance, for iceberg lettuce you need to cut it at the root, but for romaine you can gently pull up the leaves and cut them from the root base.