I planted green onions in pots from seed and then move them into different pots when they are about a few inches long. They were growing straight up for a couple of weeks, but then when they reached about 5 to 6” height, they started falling so cut it so they look healthy or you can put something in the side like a wood stick or something to help them from falling sideways.
I love to plant green because it grows all year round. This type of onions generally need about one inch of water per week. Simply stick your finger in the soil down to the second knuckle near the green onion it should grow. If the soil feels dry go ahead and water well.