Growing Onions - The Backyard Pantry

Growing bulb onions (Allium cepa) in Missouri (Zone 6b-7a). This zone is ideal for growing onions, provided you pay attention to the right planting and care techniques.

1. Choose the Right Variety

Variety Selection: There are three main types of onion varieties based on day length:
- Long-Day Onions: These onions require 14-16 hours of daylight to form bulbs and are ideal for Missouri’s climate.
  - ‘Walla Walla’: A sweet, mild onion, often grown for fresh use and storage.
  - ‘Yellow Granex’: A yellow sweet onion variety, commonly grown in Missouri.
  - ‘Sweet Spanish’: Known for its large bulbs and mild flavor, excellent for both cooking and raw use.
- Intermediate-Day Onions: These are a mix of long- and short-day onions and perform well in Zone 6b-7a.
  - ‘Candy’: Known for its sweetness and good storage potential.
- Short-Day Onions: Not ideal for Missouri, as they need shorter days to form bulbs and are better suited for the southern U.S. (e.g., ‘Texas Super Sweet’).

2. Planting Time

Indoor Starting: Start seeds 8–10 weeks before the last frost date (typically late February to early March in Missouri). Onions grown from seed need an early start.
Direct Sowing or Transplanting: Transplant onion sets or seedlings after the last frost, typically mid to late Aprilin Missouri. Direct sowing is generally not recommended for onions, as it takes longer for seeds to mature.
Frost-Free Period: Onions require a long growing season, typically 100–175 days depending on the variety. Be sure to plant after the last frost and harvest before the first frost (usually mid-September to early October in Missouri).

3. Site Preparation

Soil Requirements: Onions thrive in well-drained, loose, fertile soil rich in organic matter. The ideal soil pH is 6.0–7.0.
Soil Depth: Prepare the soil to a depth of 8–12 inches to allow for good root expansion and bulb formation.
Location: Choose a full-sun location that receives at least 6-8 hours of direct sunlight per day. Onions need plenty of sun to produce healthy bulbs.
Spacing: Space plants 4–6 inches apart in rows that are 12–18 inches apart. Proper spacing is important for air circulation and to prevent overcrowding.

4. Planting

Planting Depth: If starting from onion sets, plant the bulbs about 1–2 inches deep, with the pointed end facing upward. Transplants should be set at the same depth they were in the pot. For seeds, plant 1/4 inch deep.
Watering: Water thoroughly after planting. Onions need consistent moisture, especially during the early stages of growth. Avoid overwatering, as this can cause rot or promote fungal diseases.
Watering Method: Use a drip irrigation system or soaker hoses to water at the base of the plants, keeping the foliage dry and reducing disease risks.

5. Watering and Maintenance

Watering Needs: Onions need 1–1.5 inches of water per week, either from rain or irrigation. Keep the soil consistently moist but not soggy. Watering too frequently can lead to bulb rot, while not enough water can cause stress and poor bulb formation.
Fertilization: Onions are heavy feeders, requiring a balanced fertilizer or one with higher nitrogen content early on for leaf growth. Once the bulbs start forming, switch to a phosphorus- and potassium-rich fertilizer to promote healthy bulb development.
Weeding: Onions are poor competitors with weeds due to their shallow root systems. Mulch with organic matter like straw or grass clippings to reduce weed competition and help maintain moisture.
Pruning: Onions do not require much pruning. Simply remove any weeds that grow around the base of the plants.

6. Growth and Bulb Formation

Leaf Growth: Onions initially focus on growing their green tops. These leaves are essential for photosynthesis and overall bulb growth.
Bulb Formation: Bulb formation typically starts in late spring to early summer, when the days are longer. For long-day onions, this happens once day lengths exceed 14 hours.
Maturation: The tops of the onions will eventually begin to yellow and fall over as the plant matures and diverts energy to the bulb. The bulb swelling happens after the plant sets flowers.

7. Pest and Disease Management

Common Pests:
- Onion Maggots: The larvae damage onion roots and bulbs. Protect seedlings with row covers or insecticidal soap.
- Thrips: These tiny insects cause damage to leaves and can spread viral diseases. Control with insecticidal soap or introduce natural predators like ladybugs.
- Cutworms: These pests can cut down young seedlings. Use collars or apply diatomaceous earth to protect plants.
Diseases:
- Downy Mildew: A fungal infection that affects onion leaves. Ensure good air circulation, and avoid overhead watering. Apply fungicides if necessary.
- Fusarium Wilt: A soil-borne disease that causes wilting and yellowing. Practice crop rotation and use disease-resistant varieties.
- Neck Rot: This happens when onions are not harvested on time or stored improperly. Ensure timely harvest and proper curing.
- Onion Rust: Caused by a fungal pathogen, onion rust appears as orange spots on leaves. Prevent it by improving air circulation and removing affected leaves.

8. Harvesting

Timing: Onions are ready for harvest when the tops begin to yellow and fall over. This typically occurs in late summer to early fall (August to September).
How to Harvest: Gently pull onions from the ground or use a garden fork to loosen them. Be careful not to damage the bulbs. Leave the onions in the ground for a couple of days if the weather is dry, so the tops can dry out.
Signs of Maturity: The necks of the bulbs will become soft and the skins will become papery. Once the onions are mature, remove them carefully to avoid bruising or damaging the bulbs.

9. Storage

Curing: After harvesting, allow the onions to cure in a dry, well-ventilated area (e.g., under a shed or in a cool, dark place) for about 2 weeks. This process helps the skin harden and extends storage life.
Storage: Once cured, store onions in a cool, dry, and dark place with good air circulation. The ideal storage temperature is 35–40°F. You can store onions in mesh bags, or hang them in braids. Proper storage can keep onions for up to 6 months.
Rot and Softness: Check stored onions regularly for any signs of softness, mold, or sprouting. Discard any onions showing signs of spoilage.

10. Considerations for Missouri’s Climate

Temperature: Missouri’s summers can get hot, but onions grow well in the warm temperatures typical of Missouri’s growing season. However, extreme heat can cause stress and inhibit proper bulb formation.
Humidity: Missouri’s humid climate can encourage fungal diseases. Ensure that there is good air circulation around your onions to reduce humidity buildup.
Frost Sensitivity: Onions are very sensitive to frost. Be sure to plant onions after the last frost and harvest them before the first fall frost, which typically occurs in mid to late October in Missouri.

11. Challenges

Weather Extremes: Extreme heat or early cold spells can stress onion plants, potentially leading to poor bulb development. Use row covers to protect plants from early frosts, and consider mulching to moderate soil temperature.
Pests and Diseases: Onion maggots and thrips can cause significant damage, but regular inspection and pest control measures can help mitigate these problems.
Bulb Size: In some cases, onions may not form large bulbs if the growing conditions are not optimal. Ensuring proper spacing, consistent moisture, and adequate sunlight is essential for large, healthy bulbs.

By following these steps, you can grow healthy bulb onions in Missouri’s Zone 6b-7a with good results. Remember to choose the right variety for your region, provide consistent care, and watch out for pests and diseases to enjoy a bountiful harvest. Let me know if you need more information!