Garden Variety: The time is right for growing onions
Onions are a staple in many U.S. households and are easy to grow in the Midwest with proper timing and a little knowledge of planting methods. Give them a try this year, or use these tips to improve production if you have tried them in the past. Plan to plant anytime from now to late April in the Lawrence area. Grow onions in a traditional garden, raised bed, container, or tucked into flowerbeds to maximize space.
Knowing what and how to plant is the hardest part of growing onions. First, use onion plants or sets instead of planting from seed. Use varieties recommended for the region. Plant in early spring to allow onions to mature while conditions are most favorable – before the arrival of Kansas’ typical hot dry summers. Prepare the soil and mulch, fertilize, and water as recommended.
Onion plants are the best bet for gardeners wishing to grow large bulbing onions. Plants are usually sold bareroot (without soil) in bundles of 50 or more. They should have a small, undeveloped bulb and short green stem.
Onion sets are small bulbs without roots or stems. Sets are best for green onions but can be grown to maturity. They are usually sold in small mesh bags or in bulk bins.
Look for onion plants and sets near seed potatoes and other bulbs at the garden center. Split a bundle or bag with a friend or neighbor if only a small quantity of onions is desired.
Onions can be grown from seed, but it takes a long time to get from planting to maturity and summer heat limits growth. If seed planting is desired, start seed indoors under grow lights in January and transplant baby plants outdoors in March or April.
For bulbing onions, Kansas State University recommends Candy (yellow), Red Candy Apple (red), and Super Star (white) for best performance in Kansas. If these are unavailable, look for varieties labeled as intermediate or intermediate-day varieties. Short-day varieties are the second choice but will be smaller at maturity when grown here.
Variety selection is less important for green onions, and onions sets are often unlabeled.
Select a site in full sun with well-drained soil. Look for a site near a water source if watering/irrigation is desired. Incorporate compost and/or fertilizer into the soil prior to planting to improve drainage and fertility.
Space onion 2 to 4 inches apart in rows or blocks. If planting in containers, leave the same spacing from the edge of the pot. If incorporating into landscape beds, stick them wherever space allows.
Plant onion sets touching each other in rows or blocks. The largest bulbs will grow the fastest and are best harvested as green onions. If some onions will be left to mature, alternate large and small bulbs and plan on the small bulbs being left to grow after the large bulbs are harvested later this spring.
Place the bottom of the bulb about 1 to 1.5 inches deep. Mulch over plants or sets with straw, prairie hay, or other materials to keep weeds at bay and reduce soil temperature and moisture fluctuations. Check plantings regularly through the season and remove any weeds that appear in the rows or blocks.
Use a rain gauge or watch the weather to monitor rainfall. Onions need about one inch of water per week. Drip irrigation or other watering is beneficial when less rain is received. Containers dry out faster than the ground and may need frequent watering.
If fertilization is desired to maximize production, Kansas State University recommends applying fertilizer about three weeks after new growth appears, when plants have 6 to 8 leaves, and when plants have 9 to 11 leaves. Use a fertilizer that is all nitrogen or primarily nitrogen according to label directions or onion production guides. (The nitrogen percentage is the first number of a three-number sequence on any fertilizer sold. Look for something labeled 12-0-0, 16-0-0, etc.).
After bulbs begin to develop, onions can be harvested whenever desired for cooking and eating. When tops weaken and flop over, remove remaining onions from the soil to keep them from rotting in the ground.
Onions can be used immediately or allowed to dry outdoors for longer shelf life. Spread them on the ground in a shaded location, place them in crates or on racks, or bundle them by their tops and hang them up inside an open shed. Tops should dry within a few weeks. Then, remove dry foliage and trim roots as desired. Also remove any remaining soil. Store in a cool dry location for 1 to 4 months depending on the variety.
Green onions can also be planted in late summer for fall harvest.
USDA’s Economic Research Service estimated that 22 pounds of onions were consumed per person in the U.S. in 2019. This is the most recent year of data available and follows a trend of around 20 pounds per person per year over the last 2 decades. The total includes fresh onions and dehydrated onions used as seasoning in a wide variety of products.