To grow a long green onion you must have a pot half full with soil that is moist. If you are growing multiple you have to have them 2 inches apart you can have them indoors for 6-8 weeks. They will normally need 1 inch of water per week.. The way to know if your plant needs water you can do the finger test. Doing the finger test is simple, place your finger in the soil and if it is dry the plant needs more water. If your plant gets pest you can take out the infected plant or you could buy Pyrethum TR micro total release insecticide, this will get rid of the maggots and thrips that usually surrounding green onions. When/If you decide to have your green onions outdoors in a garden, you need to be aware of the weeds. Some weeds look nice but are very dangerous for the onion because of the amount of nutrients it takes from the plant.