It carries a cluster of small bulblets at the tip of a three-foot stalk, which bends over in autumn so that they root where they land. Tree onion (Allium x proliferum) is an heirloom perennial eaten as green stems, as shallots, or pickled in vinegar; plant it in light, sunny soil and it returns for years.
| 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.
Go ahead and plant in Mid-autumn-late autumn or in Late winter-early spring. To get things right for your “walking onion”, there are a few tips to know:
It’s all set! Time to plant! Here’s the procedure:
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.
Although it generally resists diseases well, tree onion can be attacked by the onion fly.
Bulblets of the rocambole onion can be picked in Midsummer-late summer: 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.
Tree onion follows a very simple cycle: it is planted at either end of winter, rests through the heat, gives its bulblets in high summer, then sets off walking in autumn. Here is what to expect and when.
| Stage | When | What to do or expect |
|---|---|---|
| Planting bulblets | Mid-autumn–late autumn or late winter–early spring | Press them in an inch deep, pointy tip up, 4 to 6 inches apart |
| Summer dormancy | Driest weeks of summer | Stems yellow and dry off; no watering needed, new ones follow the autumn rain |
| Harvest of bulblets | Midsummer–late summer | Bulblets detach easily; cut the bearing stems rather than tugging at them |
| Drying and keeping | A few days after picking | Spread on newspaper in the shade, in a dry, well ventilated spot |
| Natural spread | Autumn | The stem bends down and the bulblets root where they touch the soil |
Left alone, the plant repeats this cycle for several years running.
This heirloom is also offered as ‘Egyptian Walking Onion’, a name recalling how the autumn stem bends over so the bulblets root where they land; look for bulblets, since the species only reproduces through its bulbs.
Genetic analysis demonstrates that tree onion is a hybrid of two more common onion: welsh onion, and the common onion.
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!
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:
Actually, the bulblets are a way for the onion to extend its range: as the stem bends over in Autumn, the bulblets reach the ground where they take root and start a new plant! One foot at a time, out to conquer the world!
