The holes should be small enough to prevent potting soil from falling out, but large enough to let water escape.
 The bag should only be about 3/4 full, and the potting soil should be pre-moistened to help keep it inside the bag with its snipped-off corners.
 Excess soil and water can escape through the corner holes, which could create a mess if you allow it to sit out on the counter or windowsill by itself. Placing it in a tray will help you to capture and contain the mess.
 Pinch a few of the seeds in between the index finger and thumb of your dominant hand, and sprinkle them over the surface of the soil.
 Use no more than 1/8-inch (1/3-centimeter) of soil so that the seeds can absorb sufficient light.
 You only need a light spritz; anything more than that will cause the seeds to drown and cause muddy water to come gushing out of the cut-out corners of the bag.
 Leaving the bag completely open will allow too much heat and moisture to escape, but sealing it completely shut will cause the air inside to grow stale. Leave at least 1-inch (2.5 centimeters) open, "zipping" or sealing the rest of the bag's opening.
 Alternatively, you may also use a fluorescent grow light to provide supplementary light. Even using this method, the lettuce seeds need around 12 to 14 hours of light each day.
 Germination should occur within a few days to a week. Continue spraying the soil to keep it moist, and provide the seedlings with the same amount of light as before.
 This should only take a few weeks. Pick off the outer leaves first before gradually moving inward. Do not wait for the lettuce to mature into a full head when growing it in a plastic bag, since this short-cut method is not intended to nurture fully mature lettuce.
Cut off the corners of a large gallon-size plastic bag.
Fill the plastic bag with potting soil.
Place the plastic bag in a tray or on a plate.
Pour one or two dozen seeds into your non-dominant hand.
Sprinkle additional potting soil over the seeds.
Spray the soil with water.
Seal the bag mostly closed.
Allow the bag to sit out on a sunny countertop or windowsill.
Open the bag after the seeds germinate.
Harvest the leaves individually as they start to get large.
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