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.
Recommended
Varieties
Onion varieties are
classified into two categories: Long-day
(better
for cool climates) and short-day
(better
for warm climates).
Long-day
Varieties
- ‘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
Short-day
Varieties
- ‘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.
Pests/Diseases
- 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.
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Harvest/Storage
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!
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Frequently Asked Questions
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