How do you take care of an onion plant?

QUESTION: I’m thinking about planting onions in my garden this year. Are onions hard to grow? How do you take care of an onion plant? -Tom D

ANSWER: Plant onion sets outdoors as soon as the weather is cool, but not cold. In cold climate areas, plant onions as soon as the ground can be worked in the spring, typically around late March or April. In warmer regions, onions can be planted in the late fall or winter and will sit dormant over winter, but will be eager and ready to grow as soon as spring arrives. If starting your onions from seed, plant them indoors about six weeks before you plant to transplant them into the garden. To stimulate germination, provide temperatures of at least 50 degrees F.

Select a location that receives full sunlight, and where your low-lying onion plants won’t be shaded by surrounding plants. Also, be sure to select a location where onions have not been grown in the past two or three years, as it is very important to practice crop rotation when growing onions to reduce the risk of disease and pest infestations.

Provide well-draining, loose, nitrogen-rich soil that is free of clumps and compacted areas. Work in aged manure or compost in the early spring before planting. Onions are heavy feeders, so providing ample nutrition is key to getting your onions to develop large bulbs. At planting time, mix in some nitrogen fertilizer. 

Plant onion sets two to six inches apart and don’t bury them more than one inch beneath the soil. When transplanting seedlings, space plants four to five inches apart in rows 12 to 18 inches apart. Add a straw mulch between your rows to increase moisture retention and deter weeds.

Treat onions as if they are a leaf crop, not a root crop. Fertilize every few weeks with nitrogen to encourage big bulbs. Stop fertilizing when the onions push the soil back and bulbing begins. When the onions push the soil back, do not recover the bulbs with soil, as the bulb needs to emerge from the soil to mature correctly.

If you use a straw mulch, your onion plants will not require too much water, typically needing only one inch of water per week. Without mulch, or in especially dry areas, or during drought, increase water to two or three inches per week. If you prefer sweeter tasting onions, water more often. Check the soil with your finger and add water only when the topsoil is dry to the touch about a half an inch down.