A Beginner’s Guide to Growing Bunching Onions


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There are dozens of varieties of bunching onions but, for me, it’s the early cropping spring onion that tops the lot, and growing bunching onions couldn’t be simpler. By their nature, bunching onions need almost no care, to the point that if you forget about them, they will just die back and regrown next year, with an even bigger crop.

They make excellent companion plants for slug-prone vegetables and can act as a great way to separate rows of other veg too, as they take their nutrients from lower in the soil than most other leaf crops.

For beginners to onions, or beginners to gardening entirely, here’s our guide to growing bunching onions:

What are bunching onions?

Bunching Onions are one of the toughest veg in the garden, and one of the rare perennial crops you can make use of year after year. There is often confusion about what a bunching onion actually is, and it mostly comes from the confusion around exactly why they are called ‘bunching’. 

All bulbs, and all onions for that matter, will bunch. That’s just how bulbs grow, they multiply from the root plate of one bulb, usually inside a papery wrapper until they are ready to send out their own shoots and roots.

Bunching onions are no different, other than that they forgo the papery casing, and send shoots out as soon as the plant is ready to multiply. In cultivation, we duplicate this process by multi sowing (which I’ll talk more about later) because it provides a higher yield from a crop that doesn’t mind being cramped, but in reality, their natural habit is to grow one onion at a time, and to bunch by themselves the following year.

Are bunching onions the same as green onions?

This guide to growing bunching onions can be used to grow spring onions, green onions, welsh onions, Japanese bunching onions, and scallions because (you guessed it!) they’re all the same thing. Bunching onions were originally found in China, and their numerous names have come from varieties bred all over the world, but they all still share the same basic DNA (you can cross-pollinate different varieties with a bit of hard work – imagine that, a fresh red scallion with the fresh bite of a spring onion!).

The only thing to keep in mind when planting them is to leave enough space for each variety. Obviously, spring onions, which can be harvested just 8 weeks after sowing, need less space than a tall green onion, which will be ready around 4 months from sowing. 

Will bunching onions form bulbs?

Bunching onions are alliums, just like bulbing onions, leeks, or chives, but their habit of bunching up around a central plant is an energy saver, and as a result, they don’t form bulbs. Their bases are often rounded and bulbous, but they do not need peeling, and they do not separate within each bulbous base, as a white onion would.

They differ from regular white onions as their main crop is the base of the stem, rather than a bulb. If you’ve ever seen new tulips forming it’s much more akin to this as the new plants grow from one base plate, without the outer case. And while we tend not to eat the tougher stems of bulbing onions, the hollow leaves of bunching onions are famously good salad crops. Simply separate the leaves from the bulb after harvesting and use them raw.

Are bunching onions perennial, are they invasive, do they multiply?

Bunching onions are perennial onions in that one sowing can give crops for years and years, however, the individual plants grow by duplication, and eventually, the original plant will be taken over by its offspring.

While they will multiply, any gardener with more than ten minutes a year to spare will be able to keep them under control as they are very slow spreaders and, in most climates, unlikely to germinate from seed without our intervention.

  • Tip: If you ever find that they have spread beyond your wishes, just dig them up and eat them. Even in the middle of winter the entire plant can be eaten. It might be a little tougher, but chopped up and added to sweetcorn soup it’s a great taste of spring at the cold end of the year.

Guide to growing bunching onions:

How to start from seed

Now, if like me you find seeds fascinating, bunching onion seeds are truly beautiful little things; their tiny black seeds look like shards of flint, with sharp angular edges and a gorgeous satin casing. But that beauty hides some fascinating natural tricks, which make bunching onions absolute child’s play to sow.

Firstly, because they’re so angular they are incredibly easy to handle, despite their diminutive size. Secondly, they have no preference for up or down, or shallow or deep, and they will germinate any time they are safe from frost.

To sow from seed, wait until around 5-6 weeks before the last frost, and then fill a 9cm pot with any compost (they really aren’t fussy), and dip a 1-inch hole with your finger. Drop 8-10 seeds into that hole, and add water. The water will do the work of filling the hole, and that’s it. Leave them on a sunny windowsill for 2-4 weeks to germinate, and avoid watering them until they sprout. Caring too much is almost the only thing that will kill them.

  • Tip: One experiment to do if you’re growing with kids is to start them off in a glass, with the seeds sown against the glass so you can watch them germinate. You might remember this a child with beans, but onions grow in a unique way. They begin by sprouting to the side (no matter what way you plant them) and splitting into root and stem, which forms an elbow underground, which forces its way upward before flicking up out of the soil.

Transplanting bunching onions – when, how & how deep to plant.

Bunching onions of all kinds are easy-going crops, and as long as your soil is reasonably loose they will thrive. If you’re planting them as part of a crop rotation, add crushed eggshells to the soil surface as the slow release of phosphorus helps with root development, and will replace what they take out over the season.

Plant out into the garden as soon as the last frost has finished in spring, burying them slightly below the level of the soil. Their closest cousin is a leek rather than an onion, which gets its sweet white base on any part of the plant that is deprived of light. Bunching onions are the same, but planting deeper will help protect them from pigeons, and other cheeky wildlife who think they’ve found a tasty green worm.

Leave 3-4 inches between rows, so you have enough space to run your favorite hoe between lines of onions. Onions, but particularly bunching onions, are very ineffective ground cover plants, so you will almost definitely get some weed germination between plants, so leaving space to hoe is essential. 

How long until harvest?

You can plant all bunching onions at the very start of spring, and continue sowing right into mid-summer, and plant in the garden a month later. Smaller varieties will be ready to harvest just 4 weeks after planting out, but the taller bunching onions are usually ready around 8 weeks from sowing.

As a guide, if you sow in February then plant out in April, you’ll be ready to harvest between June and September depending on the variety. 

  • Tip: If, like me, you decided to experiment with leaving them in as a perennial crop, you could be eating them in early spring if the winter is mild. Imagine the excitement you get at the first daffodil of the year, accompanied by fresh produce you can pick and eat while pottering in the garden.

How to harvest bunching onions?

Harvesting bunching onions is even easier than sowing them. All you need to do is pull them out of the ground, preferably leaving one onion in the ground to provide next year’s crop.

If you are practicing crop rotation, lift the entire harvest out, and move a few to a new bed. Each onion will form its own bunch the following year, and almost all varieties are completely frost-hardy, so there is no need to cover or cut back over winter.

Bunching onions companion plants

Bunching onions are excellent companion plants for carrots, just like any allium. The smell is off-putting to carrot fly. Equally, alliums aren’t particularly palatable to slugs, so a wall of onions around your salad leaves can supposedly put them off (but I’ve had no luck at all with that trick). 

While bunching onions don’t need much themselves in the way of companionship, you will save yourself a lot of time and effort by planting them between rows of other veg or herbs, like lettuces or lemon balm. Their roots grow at a completely different height in the soil to salads and other leafy greens, which will help to keep the weeds down.

Alternatively, try growing them between rows of chamomile or winter savory. The chamomile or winter savory flavor won’t be impacted, but growing chamomile near any other veg boosts the essential oils in the plant, and therefore improves its flavor (this works with cabbages and other herbs too).  

Leeks are also a useful option to plant nearby as they deter onion fly, whose badly-behaved larvae can destroy allium crops entirely.

Conclusion

There you go, the undisputed champion of the easiest plant to grow award goes to the humble bunching onion, with all of its confusing heritage, fascinating lifespan, and unfussy habits. 

For any gardener, this beginners’ guide to growing bunching onions has hopefully given you a few tips to take home, but most of all, demystified some of the confusion around just exactly what a bunching onion is!

Check out these must-have gardening products

You don’t need much to start gardening, but some tools and products will make a difference in how comfortable and effective gardening can be for you. Here are my favorites:

  • Garden Trowel. A good garden trowel will last you many years. I love how sturdy this hand trowel from WOLF-Garten is, the metal doesn’t bend and it has a nice grip.
  • Trimming Scissors. I use them for delicate pruning and harvesting all summer long, and they’re super handy. These Teflon Trimming Scissors are extra nice because they don’t rust as easily.
  • Dutch Hoe. Dutch hoes may seem old-fashioned, but there’s nothing like a quick sweep through the topsoil to get rid of small weeds – no bending required. I love WOLF-Garten’s selection: this dutch hoe coupled with their universal handle.
  • Grow Lights. These grow lights from Mars Hydro are super strong, yet dimmable, so they fit every stage of growth. They don’t put out too much heat and are very economical.
  • Seedling Trays. There’s an art to choosing the best size for seedling trays so that it holds the perfect amount of water and gives the roots enough room to grow. These germination plugs are perfect when coupled with 1020 bottom trays
  • Liquid Fertilizer. You’ll need to feed your plants from the seedling stage, all the way to fruiting. This organic fish & seaweed blend is a very versatile option. Use it half-strength for young plants and full-strength for established plants.

Browse our list of tools, fertilizers & pesticides, indoor growing products and seed shop recommendations – we hope you find our selection useful and it saves you some time!

Patrick Kirk-Smith

I’m Patrick Kirk-Smith, a writer and obsessive gardener in Liverpool, UK (Zone 9a / H6). I’m never happier than when I’m covered in mud from a rainy day on the allotment, so here I am, I’m sharing tales and tips from my plot & garden.

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