Onions are a versatile and essential vegetable for any garden. They come in various types, including short-day, long-day, and day-neutral varieties, each suited to different climates. Known for their photoperiodic nature, onions require specific daylight hours to form bulbs. While relatively easy to grow, they do need proper care and attention to thrive.
- Common Names: Green onion, Scallion, Shallot
- Scientific Name: Allium cepa
- Plant Type: Bulb, Cool Season Vegetable
- Plant Height: 12-18 inches
- Growing Difficulty: Medium
- Growing Time: 14 weeks
- Bloom Time: Summer
- Temperature: 68-77°F
- Hardiness Zone: 4-9 (Find your hardiness zone here)
- Sunlight: Full Sun
- Soil pH: Neutral to slightly acidic
- Watering Frequency: About 1 inch per week
- Plant Spacing: 4-6 inches apart
Different Methods to Grow Onions
Growing from Seeds
Seeds are started indoors in trays filled with seed-starter mix at least six weeks before outdoor planting time. The tray is placed under artificial grow lights for 10 to 12 hours each day. The potting mix is kept damp but not soggy. When outdoor temperatures are above 50 degrees Fahrenheit, the seedlings are transplanted into the garden.
- Pros: Allows for a wide variety of onion types; can be started indoors.
- Cons: Requires more time and care; needs artificial grow lights.
Growing from Sets
Onion sets are small, immature onions that can be planted directly in the garden. They mature in about 14 weeks and are more resilient to light freezes. Sets are pressed into the soil so just the top is visible and spaced roughly 4 inches apart, with rows 12 to 18 inches apart.
- Pros: Easier and quicker than growing from seeds; higher success rate.
- Cons: Limited to the varieties available as sets; can be more expensive.
Propagating from Scraps
An inch is cut off the bottom of a fresh onion, and the outer skin is removed. The piece is dried for a day and then placed in a container filled with moist soilless potting mix. The container is kept in a warm spot with bright, indirect light. The soil is kept moist but not soggy, and green leaves should appear in about two weeks.
- Pros: Cost-effective; utilizes kitchen waste.
- Cons: Limited to the type of onion scraps available; may not produce as robust plants.
Ideal Soil and Location Requirements
Onions thrive in well-draining, loose soil rich in organic matter. They require full sun exposure, ideally in a spot free from shade and previous Allium plantings. Maintaining a neutral to slightly acidic pH is crucial for optimal growth.
When to Plant Onions
Onions should be planted in early spring or fall. Start seeds indoors 8 to 12 weeks before the last spring frost, and transplant or plant sets outdoors 2 to 4 weeks before the last frost. Ensure temperatures are above 50°F and not likely to dip below 28°F.
Growing Onions Outdoors
Growing onions from sets is the best method for outdoor cultivation due to its simplicity and higher success rate. Here’s a step-by-step guide to help you grow onions in your garden.
- Choose a sunny spot. Select a location that receives at least six hours of direct sunlight daily.
- Prepare the soil. Ensure the soil is well-draining and loose. Mix in aged manure or compost to improve texture and fertility.
- Plant the sets. Space the sets 4 inches apart in rows 12 to 18 inches apart. Press them gently into the soil so just the top is visible.
- Water regularly. Provide about 1 inch of water per week, ensuring the soil remains moist but not soggy.
- Mulch the rows. Apply a light layer of straw mulch between rows to retain moisture and suppress weeds.
- Fertilize as needed. Use a high-nitrogen fertilizer every few weeks until the soil begins to crack around the bulbs.
- Monitor growth. Keep an eye on the plants, ensuring they receive adequate sunlight and water.
- Harvest when ready. Onions are ready to harvest when the tops turn yellow and fall over. Gently bend the tops down to speed up the ripening process.
- Cure the bulbs. Let the bulbs cure in the ground for a few days before digging them up. Brush off loose soil and trim the leaves to 1-2 inches from the bulb.
- Store properly. Store the cured onions in a cool, dry place with good air circulation.
Growing Onions Indoors
Growing onions indoors is entirely feasible and can be done using shallow trays or pots. Here’s a step-by-step guide to help you grow onions indoors.
- Choose a container. Select a shallow tray or a pot that is at least 12 inches deep and has drainage holes.
- Fill with compost. Fill the container with well-draining compost or potting mix.
- Plant seeds or bulbs. Plant seeds 1/4 to 1/2 inch deep or place onion bulbs so the pointy end is just peeking over the soil.
- Water lightly. Lightly water the container and allow it to drain thoroughly.
- Place in a sunny spot. Position the container in a warm, well-lit area, such as a windowsill that receives at least six hours of sunlight daily.
- Thin seedlings. Once the seedlings are a few inches tall, thin them to 3 to 4 inches apart to allow room for growth.
- Maintain moisture. Keep the soil consistently moist but not soggy, watering as needed.
- Fertilize regularly. Use a high-nitrogen fertilizer every few weeks, following the product instructions.
- Monitor growth. Ensure the onions receive adequate sunlight and water, and adjust as necessary.
- Harvest when ready. Onions are ready to harvest when the tops turn yellow and fall over. Gently pull them from the soil.
Onions were worshiped in ancient Egypt, where their concentric circles were seen as symbols of eternal life.
Caring for Onions
- Watering: Onions need about 1 inch of water per week, including rainfall. Ensure the soil remains moist but not soggy to prevent bulb rot. During hot spells, increase watering to deter bolting and promote sweeter onions.
- Fertilizing: Use a high-nitrogen fertilizer every few weeks to support leaf growth. Stop fertilizing once the soil begins to crack around the bulbs, indicating the bulbing process has started.
- Pest Control: Common pests include thrips, onion maggots, and white rot. Use insecticidal soap to control thrips, cover crops with fine mesh netting to prevent onion maggots, and avoid soil-based compost to deter white rot.
- Harvesting: Onions are ready to harvest when the tops turn yellow and fall over. Loosen the soil around the bulbs to encourage drying, and harvest in dry weather to avoid bruising. Let the bulbs cure in the ground for a few days before digging them up.
- Storage: After harvesting, cut the roots and trim the tops back to 1 or 2 inches. Store the cured onions in a cool, dry place with good air circulation to ensure they last through the winter.
Common Challenges With Onions
Onions are generally considered easy to grow, especially if you start with sets rather than seeds. They require minimal space and maintenance, making them a great choice for both novice and experienced gardeners. In my experience, onions are quite resilient and can withstand light freezes, which is a bonus if you live in a region with unpredictable weather. However, they do need well-draining soil and full sun to thrive.
Despite their resilience, onions do come with their own set of challenges. One common issue is bulb rot, which can occur if the soil is too wet. Pests like thrips and onion maggots can also be problematic, causing damage to the leaves and bulbs. Additionally, diseases such as white rot can affect the crop if proper crop rotation is not practiced. Keeping an eye on these potential problems can help ensure a healthy and bountiful onion harvest.
Safety of Onions for Pets
Onions are toxic to cats, dogs, and other pets. If you suspect your pet has ingested onions, contact the ASPCA 24-hour hotline immediately for assistance.
Frequently Asked Questions
Can you plant a sprouted onion?
Yes, you can plant a sprouted onion. Simply cut the onion in half, leaving the sprouted part intact. Plant it in well-draining soil with the sprout facing up. Water regularly, and new green shoots will emerge, eventually forming new bulbs.
How do I prevent onion maggots?
To prevent onion maggots, use fine mesh netting or row covers to protect your plants. Rotate crops annually and avoid planting onions in the same spot each year. Applying diatomaceous earth around the base of the plants can also deter maggots.
What should I do if my onions start to bolt?
If your onions start to bolt, cut off the flower stalks as soon as they appear. Bolting is often caused by temperature fluctuations. Ensure consistent watering and mulch around the plants to maintain soil temperature and moisture levels.
Can I grow onions in containers?
Yes, onions can be grown in containers. Choose a pot at least 12 inches deep with drainage holes. Fill it with well-draining compost or potting mix. Plant seeds or sets, water regularly, and place the container in a sunny spot.
