Last year was the warmest March on record: this year it has so far been the coldest. Spring ain’t what it used to be. None the less, it’s reliably time to harvest the ‘spring onions’.
I don’t mean the things you buy in the shops as spring onions (or scallions) since I don’t grow them. Let’s face it, onions are a pain to grow from seed. You need lots of added soil fertility and fanatical weeding of things that look regrettably similar to grass seedlings. Then, just as they are starting to look after themselves, you dig them up and eat them. By this time it’s usually August, which isn’t spring, not even here in Aberdeen.
Fortunately there are two perennial vegetable species which produce excellent spring onions even when it’s still snowing and with very little fuss for the rest of the year: tree onion (Allium cepa proliferum) and welsh onion (Allium fistulosum).
Tree onion is the same species as the ordinary onion. A lot of allium species can produce either flowers or tiny bulbs called bulbils (or both) in their flower heads and tree onion is a kind of onion that goes for all bulbils. These often sprout when they’re still on the plant, giving it a tree-like appearance. The stem then usually falls over, giving the plant another of its many names – walking onion – as the bulbils put down roots and the plant ‘walks’ around the garden. It also reproduces by bulb division underground, like a shallot or a daffodil.
This gives two ways to exploit tree onions for spring onions. First you can dig up the parent plant when it resprouts in the spring, divide out some of the bulbs and replant the rest. The other way is to gather the bulbils when they are produced later in the year and plant them out into a bed where they will grow on into very well shaped spring onions. It’s kind of like having a free supply of onion sets for spring onions and yet another name for this plant is ‘topset onion’ (You can also let them grow on into bulb onions, but they tend not to be very big.). You can plant some in the autumn for spring growth as they are extremely hardy but they will also keep well if you store them in a cool, dry place, so you can make successional sowings later on in the year too.
Welsh onion is a different species from regular onion but it’s very similar to tree onion. Instead of bulbils it produces a rather fleshy flower head which can also be used as a flavouring or left to produce seed (picking the flowers stops the plants producing seed and diverts their energy back into making bulbs). Like tree onions they divide underground and can be lifted and divided as spring onions in March and April.
Both species can also be harvested by picking leaves in the summer. I find that welsh onion makes bigger and more regular-sized spring onions by division and tree onion is better for leaves, partly because you can use the bulbils to produce a really dense patch. So the best use is probably welsh onions for division in the spring and tree onion for leaves and sets for growing on. If you allow welsh onions to flower you will be very popular with the bees.
Real spring onions can be used in all the same ways that you would use the seed-grown ones. My favourite is spring onion sambar: you fry a large handful of whole spring onions until they are soft, then add tamarind, coconut and spices to make a sauce and simmer for a few minutes. It’s a great way to forget the sleet driving at the window. Search for:
Onions are a staple ingredient in cuisines around the world. Their pungent, aromatic flavor adds depth and complexity to savory dishes. But have you ever heard talk of mysterious “tree onions” that seem to sprout from branches rather than underground? This strange concept naturally leads to the question – can onions really grow on trees?!
The idea of finding onion bulbs dangling from tree limbs certainly sounds bizarre. However there is a unique type of onion that earns the name “tree onion” due to its unusual growth habit. Let’s take a look at what tree onions really are and why they have this misleading moniker.
What is a Tree Onion?
The tree onion (Allium × proliferum) is a real thing! It’s a perennial onion plant that gets its name from the way it propagates itself. Rather than producing flowers like regular onions, tree onions form clusters of small bulbils at the tops of the stems. These bulbils are essentially tiny onion bulblets that can begin sprouting and growing while still attached to the parent plant.
As the bulbils swell, the stems often start to bend under their weight. When the stalks eventually topple over and touch the ground, the bulblets will root and form new onion plants Thus, it appears as if new onions are “walking” along or spreading through a garden, leading to other colorful names like walking onions, Egyptian onions, and topsetting onions.
So tree onions don’t actually grow on trees – their bulblets just tend to sprout from the top of the bending stems, giving the visual impression of a plant growing upside down!
Where Do Tree Onions Come From?
Tree onions likely originated in central Asia and were spread around the globe by travelers. Their adaptability to a wide range of climates made them a useful food source to bring along on voyages.
The bulblets allow the plant to be easily propagated and shared. As settlers brought walking onions to new lands, the plants earned intriguing regional nicknames like Egyptian onions, Polish onions, and winter onions.
Genomic research has shown that tree onions are a hybrid between common onions (Allium cepa) and Welsh onions (Allium fistulosum). They combine the hearty, multiplying nature of Welsh onions with more bulb formation.
Growing Tree Onions
Tree onions thrive with minimal care in most temperate regions. Once established, these hardy perennials will come back year after year. All you need is a starter plant or bulbil to get your own patch going.
Here are some key tree onion growth habits:
- Tolerant of cold, heat, drought, and poor soils
- Grow 1-3 feet tall
- Form marble-sized bulbils instead of flowers
- Bulbils sprout while still attached to the stem
- Stems topple over once bulbils are heavy, spreading the plant
- Relatively pest and disease resistant
Tree onions are extremely easy keepers in the garden. Give them full sun to part shade and some occasional watering. The bulbs readily multiply to form dense clumps and will spread steadily each year.
You can also grow tree onions in containers to control spread if desired. The miniature 1-2 inch bulbs are ideal for potted cultivation.
Harvesting Tree Onions
The best thing about growing tree onions is getting to harvest different parts of the plant throughout the season:
Spring – Snip young leaves and stems when they first emerge. Use like scallions or chives.
Summer – Pick some unripe bulbils for early onion flavor. Allow remaining bulbils to fully mature on the stems.
Fall – Gather ripe bulbils once stems topple over. Use fresh or dried.
Winter – Dig up mature bulbs as needed. They store well in a cool location.
The mature underground bulbs tend to be small and elongated. Tree onion bulbs and bulbils provide a nice pungent bite and can be used cooked or raw like regular onion bulbs.
Using Tree Onions
Tree onions offer home gardeners a perpetual harvest of oniony goodness! Both the bulbs and bulbils can be used in any recipe calling for regular onions. Their strong flavor stands up well to cooking.
Some tasty ways to use up your tree onion bounty:
- Sauté bulbils as a flavorful aromatic base for soups, stews, etc.
- Pickle tree onion bulbs and bulbils.
- Add chopped bulbs or bulbils to salads, salsas, guacamole, etc.
- Use green stems and leaves as a fresh garnish.
- Caramelize mature bulbs as onion side dish or topping.
- Roast bulbs and bulbils with meats, veggies, cheese, etc.
- Dehydrate mature bulbs or bulbils for storage.
- Make tree onion powder or salt.
Let your creative cooking skills run wild! Having an endless supply of tree onions makes it easy to experiment with new recipes.
An Unusual Yet Useful Plant
While tree onions aren’t seen in stores due to their unusual growth habit, their quirky propagation is exactly what makes them a fun novelty for home gardens. They provide a perpetual harvest of oniony flavor with very little effort required.
So embrace the adventure of growing your own patch of perpetually multiplying onions! Tree onions are low maintenance, visually interesting, and offer great taste. Their “upside down” growth may seem bizarre at first, but these versatile plants are a boon for any gardener’s kitchen.
forest gardening in Scotland and beyond
Last year was the warmest March on record: this year it has so far been the coldest. Spring ain’t what it used to be. None the less, it’s reliably time to harvest the ‘spring onions’.
I don’t mean the things you buy in the shops as spring onions (or scallions) since I don’t grow them. Let’s face it, onions are a pain to grow from seed. You need lots of added soil fertility and fanatical weeding of things that look regrettably similar to grass seedlings. Then, just as they are starting to look after themselves, you dig them up and eat them. By this time it’s usually August, which isn’t spring, not even here in Aberdeen.
Fortunately there are two perennial vegetable species which produce excellent spring onions even when it’s still snowing and with very little fuss for the rest of the year: tree onion (Allium cepa proliferum) and welsh onion (Allium fistulosum).
Tree onion is the same species as the ordinary onion. A lot of allium species can produce either flowers or tiny bulbs called bulbils (or both) in their flower heads and tree onion is a kind of onion that goes for all bulbils. These often sprout when they’re still on the plant, giving it a tree-like appearance. The stem then usually falls over, giving the plant another of its many names – walking onion – as the bulbils put down roots and the plant ‘walks’ around the garden. It also reproduces by bulb division underground, like a shallot or a daffodil.
This gives two ways to exploit tree onions for spring onions. First you can dig up the parent plant when it resprouts in the spring, divide out some of the bulbs and replant the rest. The other way is to gather the bulbils when they are produced later in the year and plant them out into a bed where they will grow on into very well shaped spring onions. It’s kind of like having a free supply of onion sets for spring onions and yet another name for this plant is ‘topset onion’ (You can also let them grow on into bulb onions, but they tend not to be very big.). You can plant some in the autumn for spring growth as they are extremely hardy but they will also keep well if you store them in a cool, dry place, so you can make successional sowings later on in the year too.
Welsh onion is a different species from regular onion but it’s very similar to tree onion. Instead of bulbils it produces a rather fleshy flower head which can also be used as a flavouring or left to produce seed (picking the flowers stops the plants producing seed and diverts their energy back into making bulbs). Like tree onions they divide underground and can be lifted and divided as spring onions in March and April.
Both species can also be harvested by picking leaves in the summer. I find that welsh onion makes bigger and more regular-sized spring onions by division and tree onion is better for leaves, partly because you can use the bulbils to produce a really dense patch. So the best use is probably welsh onions for division in the spring and tree onion for leaves and sets for growing on. If you allow welsh onions to flower you will be very popular with the bees.
Real spring onions can be used in all the same ways that you would use the seed-grown ones. My favourite is spring onion sambar: you fry a large handful of whole spring onions until they are soft, then add tamarind, coconut and spices to make a sauce and simmer for a few minutes. It’s a great way to forget the sleet driving at the window. Search for:
The 2 Most Important Tips for Growing Big Onions
FAQ
Can onions grow on trees?
The tree onion (Allium × proliferum) is a perennial plant similar to the common onion (A. cepa), but with a cluster of bulblets where a normal onion would have flowers. Tree onions are also known as Spring onions, Green onions, topsetting onions, walking onions, or Egyptian onions.
Is an onion a tree or a plant?
onion, (Allium cepa), herbaceous biennial plant in the amaryllis family (Amaryllidaceae) grown for its edible bulb. The onion is likely native to southwestern Asia but is now grown throughout the world, chiefly in the temperate zones.
Where do onions grow?
Onions are grown all over the world, but they are particularly well-suited to temperate regions. Major onion-producing countries include China, India, the United States, Russia, and Iran. Within the United States, key growing regions include Washington, Idaho-Eastern Oregon, California, and West-Central Oregon.
Are tree onions edible?
Edible Uses: The plant forms small bulbs at the top of the flowering stem, these can be eaten raw or cooked[16, 33]. They have a strong onion flavour and are often used as pickled onions or added to salads[K]. As long as the bulbils are dried properly at harvest time, they store well[4].