Plant the seed about one inch deep and one and one-half inches apart. When the plants have five to 10 leaves, thin to three inches apart and use the pulled onions as scallions. Since onion roots are shallow, water them frequently and never allow them to dry during bulbing or the bulbs will be small and leathery. Preventing drought-stress in onions can also help to prevent insect problems. Don't be concerned if bulbs develop mostly out of the soil.
Thrips are the most common insect to attack onions and can emerge from the soil.
They live on weeds, so mulching and weeding are natural controls. Damaged plants will look silver. Thrips can be controlled with insecticidal soaps. By late August, the tops of onion plants will begin to lay over on the ground. Food made in the leaves will be stored in the onion bulbs.