Extension

Oklahomans have experienced weather ranging from a deep-freeze to more spring-like temperatures over the past couple of weeks. While it’s too early to get most plants in the ground, it’s the perfect time to plant onion sets or transplants. Generally, onions are planted about two to four weeks before the last expected frost.

 

Gardeners have several options when planting onions. They can start the transplants in a high tunnel or greenhouse. Another option is to purchase bare-root plants that are ready for transplanting directly into the soil. And finally, gardeners can plant onion sets.

 

Choose a site in the landscape that features both good drainage and fertile soil. Onions will grow best in full sun. Work the soil to loosen it to a depth of 4 to 6 inches. Incorporating compost or rotted manure before planting will help loosen heavy clay soils, work in about a pound of compost/manure for each square foot of soil. Fertilization should be based on soil tests, but gardeners can also mix in about a quart and a half of 10-20-10 fertilizer per 100 square feet of garden space.

 

Another fertilizing option is to fertilize twice – once when the plants are about 6 inches tall, and again when they are 12 inches tall.

 

Be sure to check the pH level of the soil. Typically, onions prefer a pH level of 6.0 to 6.8.

 

When planting onion sets, make a furrow about 1 inch deep and space the onion sets about 4-6 inches apart in rows that are 12 to 18 inches apart. Cover with soil and water thoroughly. Transplants should be spaced about 4 to 6 inches apart.

 

Keep in mind that onions have shallow roots and will require a regular irrigation to produce good bulbs– about an inch of water per week. Because of their shallow root system, gardeners will need to be careful when cultivating the plants to prevent causing damage.

 

It’s important to keep the onion bed weeded because the weeds will use valuable nutrients in the soil, as well as soak up irrigation. A layer of mulch can help suppress weed development.

 

Green onions, also known as scallions, can be harvested when they’re about 8 inches tall. Bulbing onions are ready when the tops begin to yellow and fall over – usually in late June to July. Be sure to cure the onions in a warm, dry, shaded area for seven to 10 days before storing them.