What to learn how to grow onions? here you are at the right place! Onions are a must-grow vegetable. Why? Well, where to begin! To start, onions are very easy to grow and, properly prepared, bulbs will store reliably for up to six months.
As with potatoes, there’s something deeply satisfying about the weighty harvest you can get from even a small area, and as the starting point to so many recipes there’s every reason to grow your own. So let’s not hang about: here’s our Sowing to Harvest guide to onions.
Dried or fresh, raw or cooked, onions are a foundational part of a variety of soups, salads, breads, and casseroles. Onions are easier to grow than you might think, and they’re a great plant for tucking into spare corners and along the edges of garden beds. Here’s how to grow them:
Getting Started with Onions
Bulb onions come in traditional yellow and red, but look out for white varieties too, which are often bigger, milder and great thinly sliced into salads.
For an extensive list of varieties check out our Garden Planner where you can bring up a list of varieties for every crop (including onions of course!) and read through variety descriptions at your leisure. Drop some onions into your plan, then bring up the Plant List to check the best sowing, planting and harvesting dates for your specific location.
Onions love a sunny and open site in well-drained soil enriched with organic matter such as compost or well-rotted manure. If your soil is heavy and tends to remain overly wet then grow onions in raised beds or on mounds to improve drainage.
Types of Onions
Onions come in a wide variety of shapes, sizes, and colors. The white, yellow, or red bulbs range in size from small pickling onions to large Spanish cultivars; they can be globe-, top-, or spindle-shaped.
Most types can be pulled young as green onions, but there’s also a perennial bunching type called Allium fistulosum that’s practically disease- and insect-proof and produces superior scallions.
Each bulb of the multiplier or potato onion (A. cepa Aggregatum group) multiplies into a bulb cluster. So with every harvest, you’ll have bulbs to replant for a continual supply.
The Egyptian or top onion (A. cepa Proliferum group) produces a bulb cluster at the end of a long stem with a second cluster frequently forming on top of the first. It also has an underground bulb, which is often too pungent to eat.
Other tasty plants include chives (A. schoenoprasum), garlic chives (A. tuberosum), and shallots (A. cepa Aggregatum group). Learn more about growing garlic here.
Onion varieties are classified into two categories: Long-day (better for cool climates) and short-day (better for warm climates).
- ‘Yellow Sweet Spanish’: large, round shape; yellow-white.
- ‘First Edition’: high-yielding, stores well, flavorful, creamy-yellow
- ‘Red Wethersfield’: flat bulbs that store well, white flesh, red-skinned
- ‘Stuttgarter’: sold in sets, early maturity with slightly flat shape, yellow
- ‘White Bermuda’: extremely mild, with thick, flat bulbs; white
- ‘Burgundy’: good table onion with mild, sweet white flesh, red-skinned
How to Plant Onions
- Plant onions as soon as the ground can be worked in the spring, usually late March or April. Make sure outdoor temperatures don’t dip below 20°F-6°C).
- Select a location with full sun, where your onions won’t be shaded by other plants.
- Soil needs to be well-drained, loose, and rich in nitrogen; compact soil affects bulb development.
- Add aged manure or compost to the soil in early spring, before planting. Onion plants are heavy feeders and need constant nourishment to produce big bulbs.
- At planting time, mix in some nitrogen fertilizer.
- Onion seeds are short-lived. If planting seeds indoors, start with fresh seeds each year. Start seeds indoors about 6 weeks before transplanting to the garden.
- Think of onions as a leaf crop, not a root crop. When planting onion sets, don’t bury them more than 1 inch under the soil.
- For sets or transplants, space plants 4 to 5 inches apart in rows 12 to 18 inches apart.
- Practice crop rotation with onions.
- Add mulch between the rows of onions. This will help retain moisture and stifle weeds.
Growing Onions from Seed Indoors
For the earliest start, sow onion seeds into plug trays or pots to transplant later as seedlings. This avoids the need for thinning out, encourages a more economical use of seeds and, given the protection of a greenhouse or cold frame, means sowing can start at least a month sooner in late winter.
Fill plug trays with seed-starting or general-purpose potting mix, pressing it down firmly into the cells. Sow a pinch of four to eight seeds per cell, then cover with more potting mix to a depth of a quarter to half an inch (1cm). Water with a fine spray.
Transplant the resulting seedlings while they’re still quite small to avoid disturbing the delicate roots. Make holes into prepared ground, planting each clump of seedlings about 4in (10cm) apart before firming in and watering.
Can You Plant a Sprouted Onion?
Yes, you can plant a sprouted onion, though you won’t get more onions from it. You will get lots of tasty green sprouts, however! Here’s how to do it:
- Fill a pot with potting soil and make a hole in the middle that is about the depth and width of the onion.
- Place the onion in the hole and cover with soil.
- Water and put the pot in a sunny spot.
- Harvest the green sprouts as needed for cooking.
If you get a sprout with a flower, wait until the flower goes to seed. Save the seeds for planting in the spring.
Sowing Onions Outside
Direct sowing can commence in spring as soon as the soil is workable and has warmed up a little. Rake the soil level then mark out seed drills about half an inch (1cm) deep and a foot (30cm) apart.
Sow the seeds very thinly, cover back over then water along the rows to settle them in. Thin the seedlings in stages until they’re about 2in (5cm) apart for lots of smaller onions or 4in (10cm) apart for fewer but bigger bulbs.
Covering early sowing’s or transplants with row cover or fleece helps to speed things along at the start of the season, and may help reduce the tendency to bolt.
Some especially hardy varieties of onion may also be sown in late summer to sit through winter and give an extra early crop in spring or early summer.
Growing Onions From Sets
In many regions you may be able to buy onion transplants for immediate planting. An alternative is to plant sets. Sets are part-grown onions that are super-easy to grow and save time sowing.
On the downside they don’t store as well as onions grown from seed or transplants, and they carry a higher risk of bolting (flowering) which makes the bulb too tough to eat. There are, however, heat-treated varieties available that are more resistant to bolting.
Nevertheless, sets are clear winners when it comes to convenience. Plant sets in mid spring into prepared, weed-free ground once the soil is workable and has warmed up a little.
Leave just the tips poking up from the ground and space them 2-4in (5-10cm) apart, depending on the final size of bulb you’re after. Some sets may also be planted in early autumn, to give a harvest up to two months earlier next summer.
How to Care for Onions
- Fertilize every few weeks with nitrogen to get big bulbs. Cease fertilizing when the onions push the soil away and the bulbing process has started. Do not put the soil back around the onions; the bulb needs to emerge above the soil.
- Generally, onion plants do not need consistent watering if mulch is used. About one inch of water per week (including rain water) is sufficient. If you want sweeter onions, water more.
- Onions will look healthy even if they are bone dry, so be sure to water during drought conditions.
- Thrips: To control thrips—tiny insects about as fat as a sewing needle take a dark piece of paper into the garden and knock the onion tops against it; if thrips are present, you will spot their tan-colored bodies on the paper. A couple of treatments with insecticidal soap kills them. Follow the package directions. Spray the plants twice, three days apart, and the thrips should disappear.
- Onion Maggots: Cover your emerging onion crop with a fine mesh netting. Seal it by mounding soil around the edges. The onion maggot likes to lay its eggs at the base of plants, so the netting should prevent that. You should also keep mulch away because the insects like decaying organic matter, and make sure you completely harvest your onions as the season progresses. Onion maggots are usually a problem in very rainy periods, so these precautions may be unnecessary if you have a dry season.
How to Harvest Onions
- Pull any onions that send up flower stalks; this means that the onions have stopped growing. These onions will not store well but can be used in recipes within a few days.
- When onions start to mature, the tops (foliage) become yellow and begin to fall over. At that point, bend the tops down or even stomp on them to speed the final ripening process.
- Loosen the soil around the bulbs to encourage drying.
- When tops are brown, pull the onions.
- Be sure to harvest in late summer, before cool weather. Mature onions may spoil in fall weather.
- Clip the roots and cut the tops back to 1 inch (but leave the tops on if you are planning to braid the onions).
- Let the onions cure on dry ground for a few days, weather permitting. Always handle them very carefully the slightest bruise will encourage rot to set in.
- Allow onions to dry for several weeks before you store them in a root cellar or any other storage area. Spread them out on an open screen off the ground to dry.
- Store at 40 to 50°F (4 to 10°C) in braids or with the stems removed in a mesh bag or nylon stocking.
- Mature, dry-skinned bulbs like it cool and dry.
- Don’t store onions with apples or pears, as the ethylene gas produced by the fruits will interrupt the onions’ dormancy. Onions may also spoil the flavor of these fruits (as well as potatoes).
- A pungent onion will store longer than a sweet onion. Eat the sweet varieties first and save the more pungent onions for later.
Harvesting and Storing Onions
Harvest time is approaching once most of the leaves have bent down towards the ground. Bulbs will continue to swell over the next few weeks before coloring up nicely in time for harvest.
When they’re ready, lift them up with a fork or trowel then move those destined for storing under cover to dry. Any form of cover, from an airy shed to a greenhouse is ideal. In warm, dry climates simply leave the onions where they are on the soil surface. Space bulbs out so there’s good airflow between them. Racks can help with this. This drying process, called ‘curing’, takes about two weeks and toughens up the outer skin of the onion so it will keep for longer.
Store onions suspended in nets, tied into bundles or woven into beautiful onion strings. Onions should keep until at least midwinter, and as long as spring.
Are you able to understand how to grow onions now?
If yes, then why not go ahead and start to grow onions already! Smiles
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