How to Grow Onions

Choose sweet onion varieties for enjoying raw or cooked within a couple of months of harvest. Storage types keep much longer, and will last until the following spring in the right conditions. All onions are photoperiodic – day length triggers bulb development. Our varieties are all “long day” types, suitable for northern US and Canada. Follow along with this handy How to Grow Onions from Seeds Guide and grow food.

Latin
Allium cepa
Family: Amaryllidaceae

Difficulty
Scallions are easy to grow. Bulbing onions and shallots may require transplanting and curing after harvest. By following instructions, even novice gardeners should have no trouble.

We Recommend: Patterson (ON591) was bred for a long storage life, making it an extremely economical onion to grow. Plant lots of them, and they’ll keep you going until the following spring. The onions are slightly sweet and quite pungent.
For Urban Gardeners: Scallions are actually very easy to grow, they take up very little room, and they are surprisingly cold hardy, so you can grow them from early spring until around November. Give them some cloche cover, and you can harvest all winter. They are all excellent, but Kincho (ON569) may be the closest to what you would find in the supermarket.

Timing
Start indoors in February to mid-March, and transplant in April. Overwintering onions need to be started in early July, and transplanted by the middle of August, and will be ready in June. Scallions can be direct sown every 3 weeks from April to late August. Optimal soil temperature for germination: 21-25°C (70-75°F). Seeds will emerge in 6-12 days, depending on conditions.

Starting
Transplants are preferred for home gardeners. Sow 3 seeds 5mm-1cm (¼-½”) deep in each cell of a 72-cell tray. Transplant as a clump, spacing each 12-15cm (5-6″) apart in rows 45-75cm (18-30″) apart. Scallions can be spaced at 2-5cm (1-2″) apart in rows 15cm (6″) apart.

Growing
Ideal pH: 5.5-6.5 (6.0-6.8 for scallions). Fertile and well-drained soil in full sun is essential. Add well-rotted compost and dig ½-1 cup copmlete organic fertilizer into the soil beneath each 3m (10′) of row. Keep moisture high in the top 20-30cm (8-12″) of soil. Most of the bulb should form on the surface of the soil, so don’t transplant too deeply. Bulb size is dependent on the size of the tops: the bigger the tops, the bigger the bulb. Provide August-planted scallions with the frost protection of a cloche or heavy row cover by the end of October.

Harvest
Stop watering in the beginning of August to mature the bulbs in dry soil. After half the tops have fallen, push over the remainder, wait a week and lift the bulbs. Curing is essential for long storage. Spread bulbs out in the sun for about a week, covering them at night to protect from dew. When the outer layer of the onion changes from moist to dry and crisp, it is cured. If weather is poor, cure inside. Storage: Keep onions in mesh sacks or hang in braids so they get good ventilation, and hang sacks where air is dry and very cool, but not freezing. Check them regularly and remove any sprouting or rotting onions. Well-cured storage onions should keep until late spring.

Seed Info
In optimal conditions at least 75% of seeds should germinate. Usual seed life: 1 year. Per 100′ row: 260 seeds (scallions 1.2M), per acre: 76M seeds (scallions 1,045M).

Diseases & Pests
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. Avoid overhead watering and plant in open sunny locations. Use lots of compost and practice strict sanitation and rotation procedures. Spraying with copper hydroxide every 7-14 days at the first sign of a problem may help prevent disease from spreading.

The pungent odour of onions repels many pests and also protects nearby garden vegetables.

Companion Planting
Plant chamomile and summer savory near onions to improve their flavour. Onions also work well alongside beets, Brassicas, carrots, dill, kohlrabi, leeks, lettuce, strawberries and tomatoes. Don’t plant onions near asparagus, or peas of any kind.