Mix together equal parts rich potting soil and peat moss for each of your 3-gallon pots. Fill each pot with the mixture to about 2 inches below the rim.
Set a pot trellis into one side of each pot. Pound it into the soil with sharp taps from a rubber mallet. The trellis should not shake or tilt at all.
Dig a 1-inch-deep hole in the center of each pot. Drop in a single broad bean seed and cover it gently with soil. The seed should have 6 inches of space all around it.
Set each pot on a flood tray and water the soil well. Empty extra water from the flood tray immediately. Broad beans like moist, well-drained. Wait for the top of the soil to dry before watering again.
Set the pots in a warm, sunny area. Broad beans need bright light for about four hours a day. When they sprout, wait for the first vine to reach 4 inches long. Gently wrap the vine around the bottom of the trellis. As the vine grows, continue to weave it in and out of the trellis.
Mulch your broad beans with peat moss every month. Since they are in pots, nutrients may become scarce. Help them along by making sure they have plenty to feed on.