Straw bale gardens are made by setting up the bales where you want them and then fertilizing and watering them so they start to decompose. Once the bale conditioning process is complete, it's time to plant the garden.
When deciding where to set up your bales, consider how close they are to a watering source and how much sun exposure is available. Also decide how high you want to stack the bales and whether you want a single row or multiples. Get your layout set up before you begin the watering, since wet bales are heavy.
Keep the bales moist for the next three days so they start to decompose, causing the centers to heat up. On each of the next three days, sprinkle fertilizer over each bale and water thoroughly. For the next three days, cut the fertilizer amount in half, apply the fertilizer, and water. At this point the bales should be hot from the decomposition, but they must cool before planting, which can take up to a month. Water and check them every day.
To plant, create pockets along the top of the bales, and fill them with potting soil. The depth of the holes and the spacing depends on the type of plants you're growing. Another method involves spreading potting soil over the entire bale and leveling it out. This works well for planting most lettuces since the tiny seeds are just scattered over the soil.