Wash the milk jug with warm soapy water. Rinse to remove soap residue. Dry the outside of the milk jug with a soft, dry cloth.
Draw a line around the bottom of the milk jug approximately 4 inches from the bottom. This marks the cutting line for your milk jug garden.
Cut along the marked line with a sharp knife to remove the bottom of the milk jug. Dispose of the top of the milk jug in the trash or recycle bin. Wipe out the inside of the jug with a paper towel to remove traces of water.
Puncture three to four holes in the bottom of the jug to ensure proper drainage. Use a nail or other sharp object to make the holes.
Fill the milk jug container to within 1 inch of the rim with moist seed starter. This allows room for watering your lettuce without overflowing the container.
Sow lettuce seeds to a depth of 1/8 to 1/4 inch, spaced 1 inch apart. Cover lightly with soil and press down lightly to secure the seeds and remove air pockets. Mist with a spray bottle to moisten the seeds.
Place the seeds in bright, indirect light to germinate. Optimal germination occurs at soil temperatures between 60 and 80 degrees F. Seedling may appear within two to three days or may take up to two weeks.
Move seedling to an area that receives bright light but does not overheat. Lettuce performs best at temperatures between 55 and 65 F and often bolts at higher temperatures. Leaves may also take on a bitter flavor if grown at high temperatures.
Water lettuce when the soil feels dry to the touch. Soil should feel damp but not soggy after watering.
Apply water-soluble fertilizer every two weeks, following the recommended application rate on the container.
Harvest by cutting the outside leaves once they are large enough to use. This allows the inner leaves to continue to grow and extends the harvest of your lettuce.