Tree onion, a fun and unique heirloom bulb vegetable

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Tree onion is a onion that seems to have everything upside-down: it grows onions at the tip of its stalk!

Tree onion, a summary

Botanical name – Allium cepa proliferum or Allium x proliferum
Common names – Tree onion, Egyptian onion, top-setting onion and even walking onion (favorite name!), rocambole onion
Family – Alliaceae

Type – vegetable bulb, perennial
Height – ± 3 feet (0.90 to 1 meter)
Planting distance – 4 to 6 inches (10 to 15 cm)

Exposure – full sun
Soil – Light, rather sandy and moist
Planting – beginning of Fall or Spring
Harvest – Summer

In the “Rocambole” family, let me have the onion! Great choice! After our feature on rocambole garlic, here is its cousin, the rocambole onion. It’s also commonly called tree onion. This heirloom bulb vegetable is very interesting because once it’s planted, it grows back several years in a row. This gives it yet another name: perennial onion.

Planting tree onion

Go ahead and plant in October-November or in February-March. To get things right for your “walking onion”, there are a few tips to know:

• Select a location that’s in full sun.
• The soil must be light, soft, and well broken up. Is your soil too heavy and clayish? Add some sand to it to lighten it up.
• Although tree onion loves growing in nutrient-rich substrates, a precaution you should absolutely respect is that you should never add manure or decaying organic matter (compost) right before planting. You should plan this a year ahead of time, or else your bulbs have a high risk of rotting.

It’s all set! Time to plant! Here’s the procedure:

• Loosen the soil up yet again about 4 inches (10 cm) deep. Tools like the spading fork or, better yet, the broadfork, are excellent for this.
• Level the soil if needed.
• Plant the bulblets one by one, spacing them by 4 to 6 inches (10 to 15 cm) and pressing them into the soil to about an inch deep (2-3 cm). Make sure the pointy tip is upwards.
• Cover the bulblets with ½ inch (1 cm) soil.
• If you’re growing several rows, space rows by 8 inches (20 cm) to reduce competition between plants.

Care and maintenance

No care is required once the plants have settled in well. Not even watering! Even during the driest of Summers, tree onion copes with drought by going into a dormant phase. Don’t worry if the stems start turning yellow and dry up: new ones will reappear as soon as the first Autumn drizzles fall.

Diseases and pests

Although it generally resists diseases well, tree onion can be attacked by the onion fly.

Harvest and keeping

Bulblets of the rocambole onion can be picked in July-August: at this time, they easily detach from the stem. However, to keep the stems whole and avoid damaging the base of the stems, it’s often preferable to cut those stems that are bearing bulblets. After picking all these small bulbs, spread them out on newspaper for them to dry for a few days in the shade. Make sure the area is dry and well ventilated.

Learn more about tree onion

Genetic analysis demonstrates that tree onion is a hybrid of two more common onion: welsh onion, and the common onion.

Where can I get tree onion seeds?

Well, you can’t: this species only reproduces through its bulbs!

The underground bulbs bear offshoots as they grown and spread. And of course, the bulblets at the top will also take root if planted as shown above. So get your hand on bulbs or bulblets instead of seeds!

Cooking with tree onion

The long green stems of tree onion are similar to Welsh onion in how to cook them. Once a few bulblets have appeared, you can either use them as you would shallot, or pickle them with vinegar as is done with small white onions. Simply wash them well, let them dry, and dunk them in a jar filled with white vinegar. Store the jar in a space away from light, and bring it out a month later. The bulblets will be perfectly pickled and you’ll have a delicious 100% home-made condiment to share! This might interest you:

• Perennial leek: another perennial vegetable