Alaska’s extreme cold forces gardeners to start onions indoors in March and transplant them in late May or early June. Finding the best time to plant onions in alaska is crucial for a successful harvest, as the growing season is short and unpredictable. You need to plan carefully to give your onions enough time to mature before the first frost arrives.
Onions are a cool-season crop, but they still require a long growing period. In Alaska, you cannot simply sow seeds directly in the ground in spring and expect a good yield. The soil stays cold for too long, and the days are not long enough early in the season. Starting seeds indoors gives you a head start.
Understanding Alaska’s Growing Season
Alaska’s climate varies greatly by region. Southcentral Alaska, including Anchorage, has a different growing window than the Interior, like Fairbanks, or Southeast, like Juneau. However, all areas share a common challenge: a short, intense growing season.
Onions need about 100 to 120 days from seed to full bulb. In most of Alaska, the frost-free period is only 90 to 120 days. This means you must start seeds indoors to meet those requirements. If you wait too long, your onions will be small or not bulb at all.
Day Length Matters For Onions
Onions are photoperiodic, meaning they bulb based on day length. Alaska has very long summer days, sometimes 18 to 20 hours of daylight. This is perfect for long-day onion varieties. Short-day or intermediate-day onions will not perform well here. Always choose long-day varieties for the best results.
Popular long-day onions for Alaska include ‘Walla Walla’, ‘Red Baron’, ‘Yellow Sweet Spanish’, and ‘White Sweet Spanish’. These varieties are bred to bulb when days exceed 14 to 16 hours. Alaska’s long days trigger bulbing quickly, but you still need to plant at the right time.
Best Time To Plant Onions In Alaska
The exact timing depends on your local frost dates. As a general rule, start onion seeds indoors 8 to 10 weeks before your last expected spring frost. For most of Alaska, this means starting seeds in early to mid-March. Transplant the seedlings outdoors after the danger of hard frost has passed, typically from late May to early June.
Here is a breakdown by region:
- Southcentral Alaska (Anchorage, Mat-Su Valley): Last frost around mid-May. Start seeds indoors in early March. Transplant in late May.
- Interior Alaska (Fairbanks, Denali): Last frost in late May or early June. Start seeds indoors in mid-March. Transplant in early June.
- Southeast Alaska (Juneau, Ketchikan): Last frost in late April or early May. Start seeds indoors in late February. Transplant in mid-May.
- Southwest Alaska (Bethel, Dillingham): Last frost in early June. Start seeds indoors in late March. Transplant in early June.
Check your local frost date calendar. You can find this information from the Alaska Cooperative Extension Service or local gardening groups. Adjust your planting schedule accordingly.
Step-By-Step Indoor Seed Starting
Starting onions indoors is straightforward. Follow these steps for healthy seedlings:
- Choose your seeds: Select long-day varieties suited for Alaska.
- Prepare containers: Use seed trays or small pots with drainage holes. Fill with a sterile seed-starting mix.
- Sow seeds: Plant seeds ¼ inch deep. Cover lightly with soil. Water gently.
- Provide light: Onion seedlings need 14-16 hours of bright light daily. Use grow lights or a sunny south-facing window. Keep lights 2-3 inches above the seedlings.
- Maintain temperature: Keep soil temperature around 60-70°F (15-21°C). Onions germinate best in cool conditions.
- Water consistently: Keep the soil moist but not waterlogged. Use a spray bottle to avoid disturbing seeds.
- Fertilize lightly: After the first true leaves appear, feed with a diluted liquid fertilizer every two weeks.
- Harden off: About one week before transplanting, gradually expose seedlings to outdoor conditions. Start with a few hours of shade, then increase time and sunlight daily.
Seedlings should be about 4-6 inches tall with pencil-thick stems when ready to transplant. Do not let them get leggy or root-bound.
Transplanting Outdoors
Transplanting at the right time is critical. Wait until the soil temperature is at least 50°F (10°C) and the risk of hard frost is gone. In Alaska, this is usually late May or early June. If a late frost is forecast, cover your transplants with row covers or cloth.
Prepare your garden bed in advance. Onions prefer loose, well-drained soil rich in organic matter. Add compost or aged manure before planting. The soil pH should be between 6.0 and 7.0.
Here is how to transplant:
- Dig a shallow trench about 1-2 inches deep.
- Space seedlings 4-6 inches apart in rows 12-18 inches apart.
- Place each seedling so the roots are spread out and the base of the stem is just below the soil surface.
- Firm the soil gently around each plant.
- Water thoroughly after planting.
Do not bury the stem too deep. Onions bulb at the soil surface. Planting too deep can cause rot or poor bulbing.
Caring For Onions During The Growing Season
Once your onions are in the ground, they need consistent care. Alaska’s long days and cool nights are ideal for onion growth, but you must manage water and weeds.
Watering
Onions need about 1 inch of water per week. In Alaska, rainfall can be variable. During dry spells, water deeply once or twice a week. Avoid overhead watering if possible, as wet foliage can lead to disease. Use drip irrigation or soaker hoses for best results.
Weeding
Weeds compete with onions for nutrients and water. Keep the bed weed-free, especially in the first few weeks. Onions have shallow roots, so hand-pull weeds carefully. Mulching with straw or grass clippings can help suppress weeds and retain moisture.
Fertilizing
Onions are heavy feeders. Apply a balanced fertilizer (like 10-10-10) at planting time. Side-dress with nitrogen fertilizer every 3-4 weeks during the growing season. Stop fertilizing once the bulbs start to swell, usually in mid-July.
Pest And Disease Management
Common onion pests in Alaska include onion maggots and thrips. Use row covers to protect young plants from onion maggots. Rotate crops each year to reduce disease risk. Avoid planting onions in the same spot for at least three years.
Diseases like downy mildew and white rot can occur in wet conditions. Ensure good air circulation by spacing plants properly. Remove any infected plants immediately to prevent spread.
Harvesting Onions In Alaska
Harvest time depends on when you planted. Onions are ready when the tops fall over and turn brown. This usually happens in late August or early September in most of Alaska. Do not wait too long, as frost can damage the bulbs.
Here is how to harvest:
- When about half the tops have fallen over, bend the remaining tops down gently.
- Stop watering for a week before harvest. This helps the bulbs cure.
- Loosen the soil around the bulbs with a garden fork. Pull them out carefully.
- Brush off excess soil. Do not wash the bulbs.
- Cure the onions in a warm, dry, well-ventilated area for 2-3 weeks. A garage or shed works well.
- After curing, cut off the tops and roots. Store in a cool, dark, dry place.
Curing is essential for long-term storage. Properly cured onions can last several months. In Alaska’s cool climate, you can store them in a root cellar or unheated basement.
Common Mistakes To Avoid
Even experienced gardeners make mistakes. Here are common pitfalls when planting onions in Alaska:
- Planting too early: Transplanting before the soil warms up can stunt growth or kill seedlings.
- Planting too late: Onions need enough time to bulb before the first frost. Late planting results in small bulbs.
- Using wrong varieties: Short-day onions will not bulb properly in Alaska’s long days.
- Overwatering: Onions need consistent moisture but not soggy soil. Overwatering can cause rot.
- Ignoring day length: Alaska’s extreme day length affects growth. Plan your planting around it.
- Not hardening off: Sudden exposure to outdoor conditions can shock seedlings. Always harden off gradually.
By avoiding these mistakes, you increase your chances of a successful onion harvest.
Tips For Extending The Growing Season
Alaska’s short season can be challenging, but there are ways to extend it. Using season extenders can help you plant earlier or harvest later.
Cold Frames And Row Covers
Cold frames are simple structures that trap heat and protect plants from frost. You can build one from wood and glass or plastic. Place it over your onion bed in early spring to warm the soil. This allows you to transplant a week or two earlier.
Row covers are lightweight fabric that lets light and water through but protects from frost. Use them on cold nights in late spring or early fall. They also keep pests away.
Raised Beds
Raised beds warm up faster than ground soil. They also drain better, which is helpful in Alaska’s rainy areas. Build raised beds 6-12 inches high and fill with quality soil. This can give you a head start of several days.
Mulching
Mulch insulates the soil and keeps it warm. Apply a layer of straw or leaves around your onions after transplanting. This also suppresses weeds and retains moisture.
Using these techniques, you can maximize your growing window and get the most out of your onion crop.
Frequently Asked Questions
Can I plant onion sets in Alaska?
Yes, onion sets are an option, but they are less reliable than seeds. Sets are small bulbs that were grown the previous year. They mature faster than seeds, but they may bolt (flower) early due to Alaska’s long days. If you use sets, plant them in early May and choose long-day varieties.
What happens if I plant onions too early in Alaska?
Planting too early exposes seedlings to frost and cold soil. This can kill them or stunt growth. Onions need soil temperatures above 50°F to thrive. Wait until the danger of hard frost has passed.
How do I know when to harvest onions in Alaska?
Harvest when the tops fall over and turn brown. This usually happens in late August or early September. Check the bulbs for size and firmness. Do not wait until frost, as frozen bulbs will not store well.
Can I grow onions from grocery store bulbs?
It is possible, but not recommended. Grocery store onions may be treated to prevent sprouting. They are also often short-day varieties that will not bulb in Alaska. It is better to buy seeds or sets from a reputable source.
What is the best onion variety for Alaska?
Long-day varieties like ‘Walla Walla’, ‘Red Baron’, and ‘Yellow Sweet Spanish’ are top choices. They are bred for northern climates and perform well in Alaska’s long days. ‘Copra’ is another good storage onion.
Final Thoughts
Planting onions in Alaska requires careful timing and planning. Start seeds indoors in March, transplant in late May or early June, and harvest before the first frost. Choose long-day varieties and give your onions consistent care. With the right approach, you can enjoy a bountiful harvest of sweet, flavorful onions from your Alaska garden.
Remember to check your local frost dates and adjust your schedule accordingly. Alaska’s gardening season is short, but it is rewarding. Onions are one of the most satisfying crops to grow, and the taste of homegrown onions is unbeatable. Follow these guidelines, and you will be well on your way to success.
If you are new to gardening in Alaska, start small. A single bed of onions can teach you a lot about timing and care. Each year, you will learn more and improve your results. The key is to start early, be patient, and enjoy the process.