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The Onion Family: Growing Alliums

You need space and patience in equal measure to grown onions.

If there is a plant group considered a staple in the modern diet, the onion family is it. From the ubiquitous brown onion to edible chive flowers, the diversity in the onion family is matched only by the many uses and flavours it brings to the kitchen.

The alliums are a huge genus of plants. Up to 800 species are named throughout the world although many of them not edible, domesticated or well known. The edible alliums are what we commonly call the onion family, and include bulbing onions, shallots, spring onions, leeks, garlic and chives. Their distinctive aroma comes from an array of sulphur compounds with many purported health benefits, like the ability to lower cholesterol levels, triglycerides and blood pressure, anti-clotting properties, strong anti-inflammatory components, as well as antiviral and anti-bacterial properties – quite a powerhouse of a family.

Climate And Soil

Being so well loved and with such a diversity of varieties, it is possible in many climates to have at least one member of the allium family growing almost all year. The bulbing varieties, including garlic, prefer cooler weather and it’s important to choose the correct variety for your area and season to avoid plants bolting to seed before filling out bulbs. In onions in particular, there are distinct early-, mid- and late-season varieties, so seek out advice from local growers if you are unsure.

Alliums prefer an open, sunny position and soil that is high in nutrients and organic matter with a pH close to neutral (pH 7.0). They do not tolerate acidic soils and have a low to moderate nitrogen requirement. Bulbing varieties are inclined to rot in waterlogged soil, so a freedraining site is important for success.

Pests And Disease

Plants in the allium family are susceptible to fungal diseases like downy mildew on young growth, and need good airflow and correct plant spacing. If downy mildew occurs, spray the plant with a mixture of three parts fullcream milk to 10 parts water to help to reduce its spread.

Pests like thrips and onion aphid can cause serious issues in your allium crops, especially when in large numbers. Thrip damage will show up as white flecks on the leaves, while onion aphids will literally suck the life from the plants. Encouraging natural predators like ladybirds, lacewings and hoverflies into your garden is the best way to sustainably keep any aphids under control, or use a soap and oil spray to quickly knock down the populations if you really need to.

Flowers thrown by alliums are called scapes and bees love them. By Kel Buckley
Save your biggest garlic bulbs for next season’s seed.. By Robyn Rosenfeldt
Bulbing onions will take six months to mature. By Robyn Rosenfeldt
You can harvest leeks when their stems are about 2 cm in diameter. By Bec Shann

Varieties Of Edible Alliums


Bulb onions are the common ones we are all familiar with. There are three main types: brown, red and white. Many gardeners will avoid growing onions unless they have a large area, due to the sheer number you’d need to grow to feed a family all year and the fact they take at least six months to mature. It’s important to select the correct type for your area and time of sowing, as the family is day-length sensitive, meaning their development is linked to whether daylight hours are decreasing, which happens prior to the winter solstice, or when they’re increasing, which occurs after the winter solstice.

‘Short-day’ varieties produce bulbs when the day length is reducing in autumn and ‘long-day’ varieties produce bulbs in response to lengthening daylight hours in spring. There are also varieties that are less sensitive and they’re more suited to northern areas like Queensland where the length of the days varies less. Ask your local nursery which varieties are right for you.

Onions should be harvested when the leaves start to die back, and can be dried and stored in a cool, dark place. Harvest them when the tops are still green for immediate use only, as these won’t keep well.

If you want a lower maintenance option, look out for Perennial Onions, also called Potato Onion. These multiply and produce bulbs that are smaller than a standard onion, but are more prolific in nature.


Spring onions are immature bulbing onions, picked for their stem and leaves. They often get named interchangeably with shallots, but are very different. The terms scallion and green onion are also used when talking about spring onions, and are all the same plant at various stages of maturity. The spring onion is a truly versatile plant and deserves a spot in every garden, including potted ones. To harvest, pull the whole plant out roots and all, or prolong their usefulness by cutting them off just above ground level and letting them grow again. Spring onions grow easily from seed in winter to spring, and will usually flower in the warmer months. As with all alliums, the flower heads are attractive to all kinds of beneficial bugs in the garden, so let them be when you can.


True shallots are distinctly different from spring onions, with a milder flavour and traditionally grown from bulbs, not seed. Plant bulbs five centimetres deep in autumn in warmer areas and late winter to spring in cooler areas.

As the plants grow the bulbs will multiply and, while they are smaller than a normal onion and more fiddly to peel, you can quickly create a self-sustaining shallot crop by replanting continuously in temperate areas. Harvest the leaves as you would for spring onions, use the bulbs in cooking, salads or for pickling and store once dried to use over time and for replanting.


Bunching onions do not form a bulb and can be grown from seed in spring through to autumn. They produce a clump similar to spring onions, but continue to multiply and can be divided in the cooler months, making them effectively a perennial. They produce a small seed head on the end of flower stems in summer, and are quite cold-hardy when established. They do best in temperate areas, but can be grown in the subtropics and have good disease resistance, making them a great perennial addition to a permaculture system. Harvest the stems as you would for spring onions.


A cross between the bulbing onion and Welsh onions, these easy to grow onions are also called Egyptian Onions. A cluster of bulblets grow around a central bulb, which then produces a tall stalk that also produces small aerial bulbs at the top. These bulblets grow leaves and more bulblets, with the weight of it all causing the stalk to fold over and touch the ground. This gives the bulblets a chance to set roots and grow a whole new plant, hence the name ‘walking’ onion. Curious, yet prolific and very adaptable, they can be grown from the subtropics down to cold temperate climates.

Spring onions snipped off at ground level will sprout and grow again; chive flowers are edible and add a pop of flavoursome colour to a salad. By Kel Buckley


Leeks are grown for their long stems, and don’t form a large bulb. In temperate areas, seed can be sown anywhere from spring to autumn, while in warmer climates they do best over the cooler months. Leeks are heavier feeders than other members of the allium family, and respond well to nitrogen-based fertiliser additions every few weeks to promote fast growth. They will grow over a number of months, and can be harvested from the time they are a couple of centimetres thick.

The trick with growing long white leeks is to plant your seedlings deep in the ground, up to the base of the lowest leaves. This blanches the lower part of the leek, keeping it white and sweet in flavour. You can also mound the soil or mulch around the base of the plants as they grow to achieve a similar effect. If that seems like too much work, they’ll still be delicious even if they are green. Leeks are actually a biennial plant and will eventually produce huge round flowering heads which are stunning if you have the space to leave them in the garden.

There is also a perennial leek, called a Multiplier or Perpetual leek. These prolifically produce small offsets around the main leek stem that can be divided and replanted regularly, meaning you’ll always have leeks in the garden.


If you’re short on space, chives are a fantastic perennial as they grow happily in pots. There are two common varieties, Common chives and Garlic chives. Common chives have round, tubular stems and produce edible flowers, making them a wonderful ornamental plant as well as a tasty addition for salads. Garlic chives have flat leaves, and as the name suggests, a subtle garlic flavour. Both have a clumping habit, with common chives being more cold tolerant. They can be divided as they grow, or left to their own devices. Being shallow rooted, they will benefit from regular watering and mulching, especially if growing in pots.


And finally, everyone’s favourite. Garlic! This coolweather- loving bulb is easy to grow and very rewarding – one single clove will result in an entire head of garlic. Garlic does well in aerated soil rich in organic matter and free from weeds. It can be planted anywhere from March to June depending on where you are and the variety, although it’s challenging to get good garlic in areas without cool winters. Plant the cloves (pointy end up) five centimetres deep at a spacing of 15–20 cm. Garlic doesn’t like competition, so mulch well to keep weeds at bay – but not so much that it rots. Harvest occurs in late spring or early summer. You know it is time when the lower leaves die back and the tips start to yellow off.

Hang your garlic, stems and all, undercover and in a well-ventilated place to dry. It can be saved to replant, used for months and the individual cloves can even be frozen if you want to keep them for longer. Some varieties of garlic will produce a flower head, called a scape, in the few weeks before the garlic is ready to harvest. These can be snapped off and are delicious in soups, stir fries or pesto.

They also make a pretty garnish. By Kel Buckley

Get a tissue


When an onion is cut, there are a series of reactions that cause the onion to release a compound called propanethial s-oxide into the air, which then dissolves on the surface of the eye and forms sulphenic acid. This tiny amount of sulphenic acid then stimulates the tear ducts to release liquid to dilute it in the eye. It’s thought that the amount of sulphur the plant draws from the soil influences pungency, and how strong the chemical reaction will be.

Not all members of the allium family have the same chemical reactions occurring, which is why the smell of fresh garlic is more delicious and less eye-watering than its bulbing-onion cousins.


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