When to Plant Onion Seeds?

Onions are relatively easy to grow from seed.

Homegrown onions are easy to produce, and starting onions from seed is an economical way to grow them. Some onion varieties may grow better in your climate zone than others, so research which type is best before selecting seeds. For best results, always test your soil before planting onion seeds and apply fertilizers or other soil amendments as needed.

Identification

Choose the most appropriate onion variety before purchasing seed. Onions are typically divided into two types: long-day and short-day varieties. Long-day onions form bulbs when the days last between 14 and 16 hours, and short-day varieties form bulbs when the days last 10 to 12 hours. Long-day onions tend to do better in northern states, whereas short-day onions are more appropriate for states south of the 36th parallel line.

When to Plant

Specific times to plant onion seeds vary by climate region and the type of seed. However, generally speaking, onion seeds should be planted whenever the soil is warm enough to be workable, usually in the early spring months. Onion seedlings are cold-tolerant but will not thrive if the soil freezes, so avoid planting onion seeds if there is a threat of freezing temperatures. In some areas with mild fall and winter climates, such as Texas, onion seeds can actually be planted in the fall months. Planting seeds too early may result bolting, or flowering, which may result in smaller onion bulbs.

Soil Site

Onion seeds require well-drained, fertile soils. If you have a sandy or clay soil, be sure to amend it with organic matter before planting. Place 1 to 1 1/2 inches of organic matter on top of the soil and integrate it to a depth of about 8 inches. Onions thrive in soils with pH levels between 6.2 and 6.8 and are not tolerant of very acidic soil conditions.

Pests and Diseases

Monitor onion seeds and plants carefully for signs of pests and disease. Onion thrips are a common insect pest which can cause extensive damage to plant leaves due to their feeding habits. They are usually eliminated with malathion or diazinon insecticides. Common diseases include blight, which causes leaves to yellow, and purple blotch, which results in purple splotches on plant leaves. Monitor plants carefully during warm, rainy periods, which provide a particularly favorable environment for pests and disease.

References

• Texas A&M University Extension: Growing Onions
• Ohio State University Extension: Growing Onions in the Home Garden
• Colorado State University Extension: Growing Onions from Seed