The mild taste of the Walla Walla onion can add a sweet flavor to any dish or meal where it can be used raw for the best taste. You'll want to plant Walla Walla onion sets as soon after you purchase them as possible so they don't start to go bad before they get in the ground. After planting you should start to see new growth within a few weeks and have onions ready for harvest in 115 days.
Break up the ground where you will be planting your onions so the soil is loose. Spread four inches of compost or a well-rotted manure over the soil and use the shovel to turn the soil and mix the compost in.
Drag a hand trowel or garden hoe through the soil to create a shallow trench only one inch deep. If you are going to put in multiple rows of Walla Walla onions, then be sure to space each shallow trench out by six inches.
Plant the onion sets into the trench by pushing the base of an onion set into the soil by about a ¼-inch with the roots down and the pointed tip facing up. As you plant your sets down the row be sure to space them 4 to 5 inches apart.
Bring the soil from the sides of the trench in toward the onion sets and cover them only an inch deep. Press the soil in around the onions lightly to secure them without compacting the soil.
Water the rows of onions to dampen the soil well and be sure to water as often as needed so the soil stays moist but not overly saturated over the growing season. When leaves first start to emerge from the bulbs, apply an all-purpose liquid feed to the soil.
Bend over the stalks without letting them break as the flowers form and before they can open. Let the stalks turn yellow and dry and wait about three weeks after drying to harvest the mature onions.