When to Harvest Onions: Complete Guide

Precisely knowing when to harvest onions is critical to your crop's success. Pull too early, and the bulbs will remain small. Wait too long and they'll destroy the soil. This timing is also important for the storage shelf life and flavor intensity of your garden onions .

I figured this out the hard way in my first season. Half my crop went mushy after some heavy rain. Now, I look for definitive signs that we'll discuss later. With proper timing, I get that sweet homegrown flavor that store onions lack.

Refer to the three main indicators mentioned in more detail below - neck softening, tops falling over, and changes in bulb size. These signals will help you avoid being disappointed at harvest time. Patience will reward you with crisp bulbs that will last a long time.

Onions are biennials, requiring two complete years to produce seeds. In the first year, we grow the bulb we harvest, while the second year produces flowering stalks that produce seed heads. This takes advantage of a natural two-year cycle and the requirement of having healthy bulbs to over-winter.

Observe for seed head formation after the spring bloom. Umbels form small pods that are initially green and turn tan when mature. I tend to check mine daily after the flowers wither. Several seeds, black and angular, will be ready to collect in each pod.

When most pods have turned brown, cut the seed heads with 6 inches of stem. Bundles will be upside down in paper bags. Hang in a dark, dry place for two weeks. This drying method keeps mold from forming while the seeds finish maturing.

To release seeds, rub dried pods between your hands over a bowl. Winnow out chaff outside on a breezy day. Store cleaned seeds in airtight jars with silica gel packets; they will remain viable for only one or two seasons.

Onion development consists of five distinct stages. Germination occurs when soil temperature reaches 50-75°F (10-24°C). Seeds take 7-14 days to germinate, whereas sets sprout more quickly. Moist soil is crucial, but not too wet, at this time.

To support leaf development, 55-75°F (13-24°C) air temperatures should be maintained for 4-8 weeks. Seed-grown plants typically develop more slowly than set-started plants in this situation. Usually, you will see 5-7 green leaves developing before transitioning into bulb formation, which is marked by a dark green layer of leaves at the base of the plant.

Bulb initiation occurs when the photoperiod reaches 12-14 hours of daylight. This phase lasts 2-3 weeks and requires soil temperatures around 60-70°F (16-21°C). Sets mature approximately 20 days faster than seeds during this growth stage. Proper temperatures guarantee that bulbs develop symmetrically.

In the 4-6 week bulb expansion period, maintaining consistent moisture is key. Temperature should remain below 85°F (29°C). As bulblets swell, you will count 8-13 leaves. Sets finish first but, if timed correctly, seeds produce larger storage onions.

Onions require specific temperature thresholds during their lifetime. Germination requires soil temperatures of 50-75°F, while bulb formation requires 60-70°F. Temperatures below 50°F and above 90°F will stop growth. I lost a crop when a sudden heat wave produced temperatures of 95°F in the expansion.

The timing of harvest depends on the risk of rain. Always wait 48 hours after the rain has dried. In my experience, wet soil causes 70% of bulbs to rot. Curing with high humidity leads to mold, which quickly kills storage potential.

Resort to frost protection when you expect temperatures to reach near freezing. Use row coverings to protect young plants. When protecting established onions, have heavy mulch prepared before a cold front arrives. I keep old blankets available for unexpected spring frosts that damage onion development.

Wind contributes two benefits during drying. Light breezes at up to 15 mph assist drying, but too strong, rough winds can damage the tops. Erect temporary windbreaks if your region receives strong wind. I use burlap screens to filter air, but not block it completely.

For perfect onion storage, they require 32-40°F (0-4°C) with 60-65% humidity. Humidity that is too high can create mold, while humidity that is too low can dry out the bulbs. I once lost a harvest by storing it at room temperature. Root cellars or unheated basements will naturally maintain these conditions.

Consider container types cautiously. Mesh bags allow airflow for small batches. Wooden crates help prevent bruising during bulk storage. Don't use plastic bins unless they are perforated. I use breathable cotton sacks for my kitchen supply and stacks of crates for cellar storage.

The transition from curing includes gradual temperature reduction. Move bulbs cooler at 5°F per day until reaching storage temperatures. Moisture will condense, ruining onions; this is avoided by the gradual transition to storage. I transition mine from a garage to basement over 7 days and check daily for moisture.

Use stringent sorting criteria before storage. Keep only bulbs with thin papery skins, firm necks, and no injuries. Discard ones with thick necks and any with soft spots whatsoever. I inspect every onion in bright light to check for unseen damage.

Look for maturity signs before harvest. They will have 50-90% of bulbs that are naturally fallen with necks that are papery thin. Bulbs that are firm with tight, shiny skins. Gently squeeze them. I harvest when the necks crackle when you bend them, and the bulbs stop growing wider.

To ensure a clean harvest, use the proper lifting technique. Slide a garden fork approximately six inches from the bulbs at a 45-degree angle. Although you want to loosen the soil, be careful not to pierce the onions. Grasp the onions near the base of the bulb, never at the tops. Gently twist while pulling up to ensure the roots come out intact.

Be mindful of weather timing. You want to pick them during a dry morning with at least 48 hours without any rain. Ideally, temperatures should be between 60-75°F; otherwise, you will have to deal with sunscald. I had bulbs rot when harvesting after a drizzle. During the maturity period, check the forecast religiously.

Be sure to handle bulbs very gently during post-harvest steps. Place into ventilated crates immediately after harvest. Do not drop or stack more than two layers high; place with tops covering bulbs to cure in the field. Bruising should be prevented. I usually line baskets with canvas for this purpose.

Keep in mind those harvest indicators we discussed. Fallen tops, papery necks, and firm bulbs mean the time is right. These signals will help avoid losses from harvesting too early or too late. They are better than relying on calendar dates alone.

Do not rush through the curing and storage steps. Properly drying fresh bulbs is necessary to turn them into food for the kitchen that will last throughout much of your winter. Be sure to adhere to the temperature changes and sorting methods we mentioned. Your patience at this stage will determine whether your onions last for weeks or months.

Use the guidelines for rain and timelines provided in this guide. You will now be able to correlate and expect your onions' response to the phases of growth. These best practices mitigate risk. They will thank you with better flavor and texture.

Savor the homegrown onion triumph you'll savor. Crunchy salads, flavorful soups, and caramelized masterpieces await you. That sweet flavor, which most store-bought onions lack, will become your everyday joy. Growing your own is the magic of garden-to-table.