Quick Answer
Onions can be left in the ground all year in some climates, but there are a few things to consider before doing so. Leaving onions in the ground over winter gives them a chance to continue growing roots and develop bigger bulbs for harvest the next year. However, the onions need protection from hard freezes and complete thaws. Mulching heavily around the onions insulates them in cold climates. Onions left in the ground all year may bolt or flower the second year instead of forming bulbs.
Overwintering Onions in the Ground
Many gardeners choose to dig up onion bulbs in fall for curing and storage indoors over winter. This protects the harvested crop and allows replanting of the same garden spot. However, onions are biennial plants, meaning they take two years to complete their lifecycle. The first year onions form bulbs, and the second year they flower and set seed.
Leaving onions in the ground over winter gives them a chance to continue developing roots and increasing bulb size. The larger root systems and sustained growth often leads to bigger bulbs at harvest the second year. Overwintered onions are less likely to bolt or flower the second spring.
Here are some key considerations for leaving onions in the ground all winter:
Onion Variety
Some onion varieties are better suited to overwintering than others. In general, long-day onions do better overwintered compared to short-day varieties. Long-day onions require 14-16 hours of daylight to stimulate bulb formation, so they are not triggered to bolt as quickly in spring. Some good long-day varieties for overwintering include:
– Copra
– Talon
– Patterson
– Milestone
– Red Wing
– Red Baron
Short-day varieties like Vidalia, Texas SuperSweet, and Candy are more prone to bolting if left in the ground over winter.
Hardiness Zone
Onions can be left in the ground year-round in zones 8-10 where ground rarely freezes. In colder climates, the onions need heavy mulching and protection from repeated freezing and thawing over winter. zones 3-7 can overwinter onions with proper care.
Planting Depth
Onions should be planted just 1-2 inches deep initially. However, onions left to overwinter need to be covered with 4-6 inches of mulch in fall. This protects the bulbs from hard ground freezes. Chopped leaves, straw, or hay make good winter mulches. The mulch can be pulled back in spring to allow the onions to resume growth.
Weed Control
It’s important to control weeds around onions overwintered in the ground. Weeds compete for nutrients and can impede the onions’ growth in spring. Apply mulch generously around the onions to smother weeds. Hand pull any weeds that manage to grow through the mulch.
Caring for Overwintered Onions
Onions left growing in the garden bed all year need proper care and maintenance for best results:
– Water the onions well after the ground starts to freeze in late fall. This gives them a lasting moisture source while frozen.
– Check for insect or disease damage on onions before mulching for winter. Remove and destroy any onions with signs of rot or infestation.
– Apply 4-6 inches of loose, dry mulch over the onions in late fall after several hard frosts. Leaves, straw, or hay work well.
– Pull mulch back from the onions in early spring as growing temperatures return. Allow 1-2 inches of mulch to remain around the plants.
– Fertilize the onions with a balanced organic fertilizer or compost in early spring to fuel growth. Avoid high-nitrogen fertilizers that stimulate excessive top growth.
– Water the onions regularly if spring rains are insufficient, especially once bulbs start swelling. About 1-2 inches of water per week is ideal.
– Weed consistently around the onions to reduce competition.
– Watch for flower stalks emerging from the centers of bulbs and remove them to prevent bolting.
– Harvest overwintered onions when about half of the foliage has fallen over. This indicates mature bulbs beneath the surface.
Advantages of Overwintering Onions
Here are some of the potential benefits to leaving onions in the ground through winter:
– Larger bulbs at harvest time. Continued root growth over winter allows onions to size up more the following year.
– Bigger, healthier plants. The extensive root systems of overwintered onions support vigorous top growth.
– Less bolting. Cool weather and increasing day length in spring reduces risk of premature flowering.
– No storage required. Overwintered onions don’t need to be dug up and cured for long-term storage over winter.
– Earlier spring onions. The bulbs resume growth quickly for earlier green onion harvest.
– No need to replant. Keeping onions in their same spot eliminates work tilling and replanting the area.
– Extended harvest. Overwintered onions mature earlier than those planted in spring from seed or sets. This spreads out harvest times.
Potential Problems with Overwintering Onions
While leaving onions in the ground all winter does have benefits, there are also some potential risks:
– Winter kill. Extreme cold and fluctuating temperatures without sufficient mulching can kill onions left in the ground. Young plants are most vulnerable.
– Rot and disease. Onions lacking protective mulch are prone to crown and root rot diseases. Neck rot is also more common after winter.
– Rodent/insect damage. Mice, voles and onion maggots can damage unprotected bulbs over winter.
– Weed pressure. Uncontrolled weeds stunt growth due to competition come spring. Vigilant weeding is required.
– Nutrient depletion. The long growth period depletes soil nutrients without crop rotation or fertilization.
– Premature flowering. Some varieties still bolt the second spring despite overwintering. Warm springs increase risk.
– Delayed maturity. It takes overwintered onions longer to reach full size compared to plants grown from seeds/sets.
– Reduced yields. Smaller onions with looser skins often result from overwintering. Yield per square foot is typically lower.
When to Harvest Overwintered Onions
Onions left to overwinter in the garden are generally ready to harvest a few weeks earlier than those planted the same spring. However, harvesting at the right time is still key. Here are some signs that overwintered onions are ready for harvest:
– Top fall. The green tops of the plants fall over and wither when bulbs are mature. About 50% top fall indicates harvest time.
– above soil line. Onion necks soften and bulbs push upwards slightly out of the ground when mature.
– Cracked skins. As overwintered onions reach maturity, their outer skins often crack or split open.
– Decreased girth. Mature onion bulbs stop expanding in circumference and may feel slightly softened.
– Yellowed foliage. The lower leaves turn yellow and dry up as bulbs finish growing.
– Dry conditions. Avoid harvesting after heavy rains or irrigation. Let soils dry out for few days before pulling onions.
Onions that are harvested too early won’t store well. Once half the foliage is down, use a garden fork to gently lift onions out of the ground. Brush off any soil (don’t wash yet) and allow the onions to dry for 2-3 weeks protected from sun. The dried outer layers help prolong fresh storage.
Storing Onions Overwintered in the Ground
Onions overwintered in the garden can be stored fresh for 2-4 months after harvest with proper curing and storage methods. Here are some tips:
– Cure harvested onions for 2-3 weeks in a single layer in a warm, dry, shaded spot. Avoid direct sun.
– Remove any onions with cuts, bruises or other damage that could lead to rot in storage.
– Cut off foliage to 1-2 inches from the bulbs after curing period. Roots can also be trimmed.
– Place cured onions in a breathable container like a mesh bag, crate or basket. Avoid plastic bags.
– Store in a cool (35-50°F), dry location with good air circulation and low humidity. Basements or cellars work well.
– Check regularly for rotting bulbs and remove immediately to prevent spread. Wipe down containers to discourage mold.
– Use damaged or softened onions right away. Refrigerate cut onions to extend freshness a few extra weeks.
– Onions keep 2-4 months typically. Discard any remaining bulbs that show signs of shriveling or sprouting.
Conclusion
Leaving onions to overwinter in the garden beds provides some potential benefits but also carries risks. With the right onion variety, climate conditions, and care, gardeners in many regions can overwinter onions successfully. Key practices like weed control and heavy mulching in fall help ensure the onions survive cold snaps and resume growth in spring. While total yields may be lower, overwintering can produce earlier, larger onions come harvest time.
| Onion Variety | Days to Maturity | Best Uses |
|---|---|---|
| Copra | 100-120 days | Long storing, crispy bulbs |
| Red Wing | 100-110 days | Red onions for salads, sandwiches |
| Candy | 85-95 days | Sweet onions for raw uses |
