One of the easiest ways to guarantee germination of your green bean seeds is to germinate them in water. When kept moist for a few days, the outer shell of the bean cracks open, and the bean can begin to sprout without having to push through any soil in the process. Germinating your seeds in water can increase your germination rate as well as cut down on potential diseases that prevent the seedling from growing.
Wet a paper towel or napkin to dampen it well. Don't wet it so much that the towel is dripping or pouring off excess water.
Lay the paper towel on a clean surface such as a counter or plate. Spread a single layer of seeds onto half of the towel, leaving a little room between each seed and around the edges. Fold the other half of the towel over, covering the seeds.
Wrap a second damp paper towel around the first to add another layer of moisture. Secure the ends by folding them over so that no seeds can fall out or be exposed to air.
Place the wrapped seeds into a zip-top bag or jar and seal shut to hold the moisture in. Set the bag or jar in a warm area, but out of direct sunlight. The top of a fridge is typically sufficient.
Check your seeds for sprouting after five days by opening the paper towel slightly and peeking in without unwrapping all of the seeds. If they haven't germinated, reseal the bag or jar and leave for another five days.
Plant your sprouts into seed trays or in your garden bed after the threat of frost has passed.