Onion Gardening in Zone 3 Alberta: A Guide to Success in Cold Climates
Onions (Latin: Allium cepa) are a staple in many kitchens, prized for their flavor and versatility. Successfully growing them in Zone 3 Alberta, which is well known for it’s cold winters and a short growing season, takes a little prep work but nothing too time consuming or expensive.
This post provides practical tips, from choosing the best varieties, to managing planting schedules, and care for a thriving onion garden in Zone 3 Alberta.
Third in our “growing” series after Growing Potatoes in Zone 3 Alberta, and Growing Tomatoes in Zone 3 Alberta.
Understanding Zone 3 Conditions
Zone 3 Alberta has an average annual minimum temperature of -34°C to -40°C (-30°F to -40°F). The growing season is brief, typically lasting only 90–120 days. Successful gardening here requires:
- Choosing crops that can thrive in cooler climates.
- Overwintering or early starting of seeds indoors.
- Maximizing the use of the frost-free period.
- Preparing and amending your soil and beds to support growth during the short season.
Choosing Onion Varieties for Zone 3
When gardening in Zone 3 Alberta, selecting the right onion varieties is vital to success. Look for cold-hardy, long-day or day-neutral onions that require 14–16 hours of daylight to form bulbs*. These onions generally store well. Here are some recommended varieties:
- Patterson: An improved variety from the discontinued Cobra, renowned for its excellent storage and reliable yield.
- Redwing: The ultimate storage red onion, with a long storage life.
- White Wing: A flexible, versatile onion with mid-range storage.
You’ll also want to find out if the desired varieties do better with overwintering (planting before winter, usually around late August) or spring planting, if you have the option.
Walla Walla, a well known and enjoyed sweet onion, doesn’t store very long, and grows biggest and mildest when overwintered. Other varieties will have their own needs. Keep that in mind when planning your onion patch!
*Short-day onions grow best in the Southern US or similar warm climates.
Starting Onions: Seeds vs. Sets vs. Transplants
Onions can be started in three ways. In Zone 3 Alberta, the method you choose depends on your timeline and resources:
- Seeds: Overwinter or start indoors 10–12 weeks before the last frost to give your onions a head start. This method offers the most variety options (see next section for how-to).
- Sets: These small onion bulbs are easy to plant and grow quickly. They’re ideal if you prefer simplicity and don’t need rare varieties.
- Transplants: Young onion plants can be purchased from nurseries and directly transplanted into your garden after the last frost.
How to Start Onion Seeds Indoors
Starting onion seeds indoors ensures a long enough growing season in our climate. Follow these steps for success:
1. Timing
- Begin sowing seeds indoors 10–12 weeks before the last frost date in your area. For Zone 3 Alberta, this typically means starting in late February or early March.
2. Choosing Containers
- Use seed trays, small pots, or any container with drainage holes.
- Shallow containers work well since onions don’t require deep soil for early growth.
3. Preparing the Growing Medium
- Use a light, well-draining seed-starting mix.
- Avoid garden soil, which may be too heavy and can harbor pests or diseases.
4. Planting Seeds
- Fill your containers with moistened seed-starting mix.
- Sow seeds ¼ inch deep and ½ inch apart. If planting densely, you’ll need to thin them later.
- Cover lightly with soil and mist to settle the seeds.
5. Providing Optimal Conditions
- Place containers in a warm spot (21-25°C / 70–75°F) to encourage germination. A seedling heat mat can help maintain consistent temperatures.
- Once seedlings emerge (7–10 days), move them to a cooler area (15-18°C / 60–65°F) with bright light to prevent legginess.
6. Lighting
- Onions require 12–16 hours of light daily. Use grow lights if natural light is insufficient.
- Position lights 2–4 inches above seedlings, adjusting as they grow.
7. Watering and Fertilizing
- Keep the soil evenly moist but not waterlogged.
- Young onions generally do not require fertilizer.
8. Trimming
- When seedlings reach 4 inches tall, trim the tops to 2–3 inches. This prevents them from becoming floppy and encourages stronger growth.
9. Hardening Off
- About 1–2 weeks before transplanting outdoors, gradually expose seedlings to outdoor conditions. Start with an hour of sunlight daily and increase the exposure time each day.
By following these steps, you’ll have healthy, robust onion seedlings ready to thrive in your Zone 3 garden.
Preparing the Soil
Onions thrive in loose, well-drained soil with plenty of organic matter. Follow these steps to prepare your garden beds:
- Test and Amend Soil: Aim for a soil pH of 5.5-6.5. Add compost or well-rotted manure to enrich the soil.
- Improve Drainage: Use raised beds or loosen heavy clay soils to prevent waterlogging.
- Add Nutrients: Onions are heavy feeders. If needed for poor soil quality, incorporate a balanced fertilizer before planting.
Planting and Spacing
Here are key planting guidelines for onions in Zone 3 Alberta:
- Timing: Overwinter in August/September or start seeds indoors in late winter (February–March). Transplant seedlings or sets outdoors as soon as the soil is workable in spring, around 2–3 weeks before the last expected frost.
- Spacing: Space onions 6 inches apart in rows 18-30 inches apart in full sun. Proper spacing ensures each bulb has room to develop.
- Depth: Plant sets 1 inch deep, with the pointed end up. When transplanting seedlings, bury them just enough to cover the roots.
Care During the Growing Season
Onions require consistent care for healthy bulb development. Follow these tips:
1. Watering
- Provide 1 inch of water per week, more during dry spells. Allow soil to dry out a between waterings.
- Avoid overhead watering to reduce the risk of fungal diseases.
2. Weeding
- Onions compete poorly with weeds. Regular weeding is crucial.
- Mulch around plants to suppress weeds and retain soil moisture.
3. Fertilizing
- Apply a balanced fertilizer once or twice during the growing season.
4. Pest and Disease Management
- Botrytis blast and downy mildew are common leaf diseases. One starts with white spots and streaks, the other with purple-grey areas on leaves. Leaves wither from the top down and plants die prematurely. Separate the overwintered and spring crops because disease starts in older plants and moves to younger (from West Coast Seeds).
- Prevent diseases such as onion rot by avoiding overwatering and rotating crops annually.
Harvesting and Storage
When the tops of your onions turn yellow and flop over, it’s time to harvest. Follow these steps for the best results:
- Preparation: Stop watering in early August to mature the bulbs in dry soil.
- Harvesting: Gently loosen the soil and pull onions by hand. Avoid bruising the bulbs.
- Curing: Let onions dry in a warm, airy space for 2–3 weeks until the necks are completely dry.
- Storing: Store cured onions in a cool, dark, and dry location. Varieties like Patterson can last for several months when stored properly.
Tips for Extending the Growing Season
To make the most of Zone 3 Alberta’s short growing period, utilize these tips:
- Overwinter or start seeds 10-12 weeks before the last frost for your area.
- Onions are hardy. Don’t stress about heavy frost, light freezes, or snow.
More Resources
US States and their universities have a fantastic system called the Cooperative Extension System. They are an absolute treasure trove of information about a whole lot of rural life topics.
Final Thoughts
Growing onions in Zone 3 Alberta requires advanced preparation but not much else in the way of unusual work, and the results are well worth the effort.
Have Questions or Tips?
Do you grow onions in Zone 3? Share your experiences and tips in the comments below!
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