When is the right time to harvest onions? - Plant Care Guide

The right time to harvest onions (for storage) is typically in late summer or early fall, when the plant's tops (foliage) have naturally matured, yellowed, and begun to fall over. This natural "neck fall" signals that the bulb has finished swelling and is redirecting its energy for dormancy. For green onions (scallions), harvest any time they reach a usable size. For sweet onions, harvest promptly when mature. Correct timing is crucial for optimal bulb size, flavor, and storage potential.

How Do I Know When Storage Onions Are Ready to Harvest?

You know when storage onions are ready to harvest primarily by observing the natural senescence (dying back) and falling over of their green tops. This is the most crucial indicator that the bulb has finished swelling and is preparing for dormancy, developing a papery skin essential for long-term storage.

• Foliage Yellowing and Falling Over (The Key Sign!): This is the definitive signal. The onion's green leaves (tops) will begin to turn yellow, then brown, and finally dry out. Crucially, the neck (where the leaves emerge from the bulb) will soften and the tops will naturally fall over, lying flat on the ground.
  • Timing: This usually happens in late summer or early fall, typically 3-4 weeks after the foliage begins to yellow, and around 90-120 days after planting, depending on the variety.
  • Why: This physiological process indicates that the plant has redirected all its energy from leaf growth to bulb development, which is now complete. The bulb is essentially signaling it's finished growing.
• Papery Skin: As the tops die back, the outer layers of the bulb will begin to form a dry, papery skin. This dry skin is vital for protecting the bulb during storage.
• Firmness: The bulb itself should feel firm and solid when gently squeezed.
• Size: The bulbs should have reached their full, mature size for the variety.
• Time from Planting: While variable, most storage onions take approximately 100-120 days from planting onion sets or 150-180 days from seed to reach maturity. However, the visual cues of the foliage are more reliable.

Do NOT wait until the entire top is completely brown and dry, as this could leave the bulbs susceptible to rot before lifting. The "neck fall" is your signal.

How Do I Know When Green Onions (Scallions) Are Ready to Harvest?

You know when green onions (scallions) are ready to harvest simply by their usable size, as they are harvested for their green tops and small white bases, not for bulb development. There's no specific "ripeness" stage like storage onions.

• Height: Begin harvesting when the green tops are at least 6-8 inches tall, or whenever they are large enough for your culinary needs.
• Thickness: The white base of the onion (just above the roots) should be pencil-thin or slightly thicker.
• Tender Leaves: The leaves should be fresh, vibrant green, and tender, not tough or showing signs of yellowing or stress.
• Taste Test: You can always snip a small piece and taste it for desired flavor intensity.
• Time from Planting: Green onions are much faster, typically ready in 3-4 weeks from seed or 2-3 weeks from sets.

Harvesting Technique:

• Pull Entire Plant: For a full scallion, gently pull the entire plant from the soil, roots and all.
• Cut-and-Come-Again: For continuous harvests, cut the green tops about 1 inch above the soil line, leaving the white base and roots in the ground. The plant will regrow new green shoots, allowing for multiple harvests.

You can harvest green onions continuously throughout their growing season until temperatures become too hot (causing them to bolt) or too cold (slowing growth).

What is the Best Technique for Harvesting Storage Onions?

The best technique for harvesting storage onions involves a careful two-step process: lifting the bulbs and then curing them properly. This ensures the bulbs develop a tough, papery outer skin and dry completely, which is essential for long-term storage.

Step 1: Lifting the Onions

1. Wait for Neck Fall (Crucial!): As described, wait until about 50-75% of the onion tops have naturally yellowed and fallen over. This signals the bulbs are mature.
2. Loosen the Soil (Optional but Recommended): About 7-10 days before you plan to lift the onions, you can gently loosen the soil around the bulbs. This can be done by carefully pushing a spade or garden fork into the soil a few inches from the bulb, gently rocking it to break some of the smaller roots without fully lifting the onion.
   • Why: This helps speed up the drying process of the neck and encourages the bulb to develop its papery skin. Some gardeners simply wait for neck fall and then proceed to lifting.
3. Stop Watering: Cease all watering for about 1-2 weeks before lifting to allow the soil to dry out.
4. Lift Carefully: Choose a dry, sunny day. Gently loosen the soil around each bulb with a garden fork or trowel. Carefully lift the onions from the ground, being extremely careful not to bruise the bulbs, as any damage can lead to rot in storage.
5. Leave Tops Attached: Keep the tops (foliage) fully attached to the bulbs. Do not cut them off at this stage.

Step 2: Curing the Onions

1. Place in a Warm, Dry, Well-Ventilated Location:
   • Method: Lay the lifted onions in a single layer (do not pile them up) in a location that is warm (75-85°F / 24-29°C), dry, and has excellent air circulation. This can be on screens, racks, or even spread out on a tarp in a protected sunny spot outdoors (if no rain is expected).
   • Why: Curing allows the outer skin to dry and harden, seals the neck, and drives moisture out of the bulb, preventing rot.
2. Curing Duration: Allow them to cure for 2-4 weeks, or until the necks are completely dry and tight, and the outer skins are papery and fully formed.
3. Clip Tops and Roots: Once fully cured, the dry tops can be cut off, leaving about 1 inch of stem above the bulb. Trim off any long roots.
4. Inspect: Discard any soft, damaged, or diseased bulbs. Only store firm, healthy onions.

Proper harvesting and curing are essential for maximizing the storage life of your onion crop.

How Does Onion Variety Affect Harvest Time?

Onion variety significantly affects harvest time, primarily due to their photoperiod (day length) requirements for bulbing. Onions are classified as "short-day," "long-day," or "intermediate-day," dictating when they will form bulbs based on the amount of daylight they receive.

• Day Length Categories (Crucial!):
  • Short-Day Onions:
    • Requirement: Form bulbs when day length is 10-12 hours.
    • Best for: Southern states (USDA Zones 7-11) where winters are mild. Plant in fall for early spring/early summer harvest. They won't bulb well in northern summers.
    • Harvest Time: Typically ready for harvest in late spring to early summer.
  • Long-Day Onions:
    • Requirement: Form bulbs when day length is 14-16 hours.
    • Best for: Northern states (USDA Zones 6 and colder) where summers have long daylight hours. Plant in early spring for mid-to-late summer harvest. They won't bulb well in southern short days.
    • Harvest Time: Typically ready for harvest in mid-to-late summer.
  • Intermediate-Day Onions (Day-Neutral):
    • Requirement: Form bulbs when day length is 12-14 hours.
    • Best for: Transitional zones (USDA Zones 5-7), or generally adaptable across wider regions.
    • Harvest Time: Typically ready for harvest in mid-summer.
• Days to Maturity (DTM): Seed packets and plant tags will provide a "Days to Maturity" (DTM) range, usually from transplanting or setting out. This indicates the relative time frame but should be paired with the day-length type.
• Sweet vs. Storage Onions:
  • Sweet Onions: Often have higher water content and thinner skins. They are often short-day varieties. They typically don't store as long as pungent storage onions and should be consumed sooner.
  • Pungent Storage Onions: Tend to have tougher, more papery skins. Often long-day or intermediate-day types. Bred for longer storage.

Always choose an onion variety that is appropriate for your specific geographical location's day length to ensure proper bulbing and harvest. Planting the wrong type will result in failure to bulb.

How Does Harvesting Impact Future Onion Production (for Next Season)?

For storage onions, harvesting generally means the end of that plant's production for the season; the bulb is a single harvest. However, harvesting can indirectly impact future onion production through seed saving or management of volunteer plants. For green onions (scallions), harvesting encourages future production.

For Storage Onions:

• One-Time Harvest: A mature storage onion bulb is the result of the plant's entire life cycle for that season. Once you harvest it, that individual plant is done.
• Impact on Seed Saving: If your goal is to save seeds, you would typically allow a few plants to remain in the ground beyond bulb harvest. These will send up a flower stalk in their second year, produce seeds, and then die. This is how biennial onions (many storage types are biennial but grown as annuals) reproduce.
• Volunteer Plants: If you leave bolted or unharvested storage onions in the ground, they will produce seeds. These seeds can then germinate and produce volunteer onion plants next season, which may or may not bulb well.
• Crop Rotation: Proper harvesting and cleanup of storage onions allows for healthy crop rotation practices, which is crucial for preventing disease buildup and supporting future onion crops.

For Green Onions (Scallions) - Cut-and-Come-Again:

• Promotes Regrowth: If you harvest green onions using the "cut-and-come-again" method (cutting the green tops about 1 inch above the soil line, leaving the white base and roots), the plant will readily regrow new green shoots, allowing for multiple harvests throughout the season. This actively encourages future production from the same plant.
• Staggered Planting: For a continuous supply of green onions, many gardeners plant small batches of seeds or sets every few weeks, rather than relying solely on regrowth from a single planting.

So, while a harvested storage onion is gone for good, the method of harvesting green onions (scallions) directly promotes a continuous yield from the same plant.

What Are the Risks of Harvesting Onions Too Early?

The risks of harvesting onions too early primarily involve smaller bulb size, reduced flavor, poor storage quality, and a less developed papery skin, which compromises their long-term viability.

• Smaller Bulb Size (Crucial!): This is the most significant drawback. If you harvest before the tops naturally fall over, the bulb has not finished swelling. It will be considerably smaller than its genetic potential, resulting in a significantly reduced yield.
• Reduced Flavor Development: The complex sugars and aromatic compounds that give onions their distinctive flavor continue to develop as the bulb matures and the tops die back. Harvesting too early results in a milder, less pungent, or less sweet flavor.
• Poor Storage Quality (Crucial!): Onions harvested too early will have thick, green, or undried necks. The outer skin will not have fully formed its protective, papery layers.
  • Impact: The moist neck and thin skin are highly susceptible to rot and fungal diseases in storage, leading to rapid spoilage and a very short storage life.
• Reduced Curing Success: The curing process (drying the neck and outer skins) is less effective on immature bulbs, making them even more vulnerable to rot.
• Weaker Bulb: An immature bulb may not be as firm and robust as a fully mature one, making it more susceptible to bruising and damage.
• Incomplete Development: The entire physiological process of the onion storing energy for dormancy is interrupted, impacting its quality.

To avoid these risks, always be patient and wait for the definitive signs of maturity – the natural yellowing and falling over of the tops – before harvesting storage onions.

What Are the Risks of Harvesting Onions Too Late?

The risks of harvesting onions too late (i.e., leaving them in the ground long after their tops have fully fallen over and dried) primarily involve increased susceptibility to rot, pest damage, bolting/re-sprouting, and reduced storage quality.

• Increased Risk of Rot: This is the primary concern. After the necks have fallen and the bulbs have ostensibly finished curing in the field, prolonged exposure to moisture (rain, dew) in the soil can cause the bulbs to absorb water again or become vulnerable to fungal and bacterial rot. The protective outer skins can soften or crack.
• Pest and Disease Susceptibility: Onions left in the ground too long are more susceptible to soil-borne pests (e.g., onion maggots) and diseases that can penetrate the softening skins.
• Bolting / Re-sprouting: In some cases, if left in the ground, onions may attempt to re-sprout or send up new green growth, which uses up stored energy from the bulb, making it less suitable for storage. They may also send up a flower stalk (bolt), which also diminishes quality.
• Splitting: Very mature onions, especially after additional moisture, can sometimes split or crack while still in the ground.
• Reduced Storage Quality: Even if they don't rot or re-sprout, bulbs left too long can have compromised outer skins or a softer texture, leading to a shorter storage life.
• Damage from Freezing: If a hard freeze occurs while onions are still in the ground, they can suffer freeze damage, becoming mushy and inedible.

To avoid these risks, harvest your storage onions promptly after their tops have fully fallen over and dried, and then move immediately to the proper curing process. Timeliness is crucial for maximizing storage potential.

How Does Weather Affect Onion Harvest Time?

Weather significantly affects onion harvest time, primarily by influencing the plant's growth rate, ripening process, and the crucial curing stage. Gardeners must adapt their harvest plans to prevailing weather conditions.

• Sunny, Dry Weather (Ideal for Harvest & Curing):
  • Impact: Consistently sunny and dry weather, especially as onions approach maturity, is ideal for harvesting and curing. It encourages the tops to dry naturally and facilitates rapid curing once lifted.
  • Benefit: Leads to well-cured bulbs with excellent storage potential.
• Cool, Wet Weather (Delays Maturity, Increases Risk):
  • Impact: Prolonged cool, wet weather as onions near maturity can delay the natural falling over of the tops. It also keeps the soil soggy.
  • Risk: Increases the risk of fungal diseases and rot in the bulbs while they are still in the ground, and makes proper field curing difficult.
  • Action: If tops aren't falling and persistent wet weather is predicted, you might gently "lodge" the tops (bend them over by hand) to encourage the neck to soften, but be cautious.
• Heatwaves (Accelerates Maturity, Can Cause Stress):
  • Impact: Very hot temperatures can sometimes accelerate the ripening process, causing tops to fall prematurely or even cooking the bulbs if the soil becomes too hot.
  • Risk: Can lead to smaller bulbs if forced to mature too quickly.
• Early Frost (Forces Harvest):
  • Impact: An unexpected early hard frost will damage onion tops and can harm the bulbs if left in the ground.
  • Action: If a hard frost is predicted and onions are nearly mature (even if tops haven't fully fallen), it's best to harvest them immediately. Lift them carefully and bring them to a protected, warm, dry area for curing.

Monitoring weather forecasts is essential for timing your onion harvest effectively, ensuring the best conditions for both maturity and successful curing.

What is the Curing Process, and Why is it Essential for Storage Onions?

The curing process is a critical post-harvest step for storage onions, involving drying the outer skin layers and the neck of the bulb in warm, dry, and well-ventilated conditions. It is absolutely essential for long-term storage, preventing spoilage and extending shelf life.

Here's why curing is so important:

1. Forms a Protective Skin: Curing allows the outer layers of the onion to dry thoroughly and form a tough, papery, protective skin. This skin acts as a natural barrier against physical damage, moisture loss, and pathogen entry.
2. Seals the Neck: The neck of the onion, where the foliage was attached, is a moist, open wound when first harvested. Curing causes this neck to dry out and seal completely.
   • Why: A well-sealed neck is crucial for preventing the entry of moisture and disease-causing fungi or bacteria into the bulb, which would lead to rapid rot in storage.
3. Dries Excess Moisture from Bulb: Curing draws out excess moisture from within the bulb itself. This reduces the internal water content, making the onion less susceptible to spoilage.
4. Enhances Flavor: While not the primary purpose, some flavor development can continue during the curing process.
5. Extends Storage Life: Properly cured onions can be stored for months (depending on the variety) without rotting or sprouting, providing a consistent supply for culinary use. Uncured onions will spoil quickly.

Key Curing Conditions:

• Warmth: Ideal temperatures are between 75-85°F (24-29°C).
• Dryness: Very low humidity is crucial.
• Air Circulation: Excellent airflow all around the bulbs is essential. Lay them in a single layer on screens or racks.
• Duration: Typically 2-4 weeks, until necks are dry and crispy, and outer skins are papery.

Skipping or improperly executing the curing process will dramatically shorten the storage life of your onion harvest, often leading to rapid spoilage.