Tree onion: how to grow, care for & harvest walking onions

The tree onion or Egyptian walking onion is a pretty rare plant. Nevertheless, with its striking appearance, its many uses and easy care, it makes an interesting addition to any garden.

The tree onion (Allium x proliferum or Allium cepa var. viviparum) is curious looking: The small bulbs do not form underground, but rather above ground directly on the stalks, forming several tiers. But this is not just an attractive onion, it is also delicious and most parts of the plant can be enjoyed nearly all year round. Read on to find out everything about the cultivation of tree onions, from planting to harvesting and use.

Tree onion: origin and characteristics

The tree onion, also known as the Egyptian walking onion, is a fairly unknown member of the Allium genus. This onion species, which is thought to have originated in Siberia, is also hardy here and even evergreen in mild winters. Its round, hollow stalks can be harvested all year round. The plants can grow up to 80cm high and form small bulbs instead of flowers from June until September. It is not uncommon for these to sprout on the stalk, forming a second, sometimes even a third tier. As summer draws to a close, the stalks become top-heavy and fall over, creating new plants where the bulbs hit the ground – hence the name walking onion. This method of reproduction is also reflected in one of its Latin names, Viviparum, which means “giving birth to life”.

Planting tree onions

Tree onion plants can be bought in some specialist shops. Often, however, the small bulbs are passed on from gardener to gardener. This is the only way to propagate walking onions, as the plant does not flower and therefore does not produce seed.

Tree onions are not too fussy when it comes to their location and they do not require a huge amount of nutrients either. They prefer sunny to semi-shady locations on limey, humus-rich and loose soils with a pH above 6.5.

Important: Allow a cultivation break of at least 4 years between planting tree onions and other allium plants such as onions, leeks and spring onions, otherwise crop rotation diseases may occur.

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Planting tree onion bulbs step by step:

• Remove weeds and hoe the soil to loosen and prepare the bed.
• Soils in our regions naturally acidify over time. One factor that increases this natural process is fertilising. Therefore, it can be helpful to work some lime into the soil before planting. If you are unsure whether liming is necessary, first determine the pH value of your soil.
• Space the bulbs 30-40cm apart and press lightly into the soil. Alternatively, you can also put the bulbs about 5cm deep into the soil.
• After sowing it is important to make sure that the soil does not dry out. But it should also never be too wet around the onion because this can cause the tree onion to rot and not sprout.

Tip: It is best to plant healthy looking bulbs that have not yet sprouted. This increases the chances of good growth.

Egyptian walking onion care

Tree onions are easy to care for. Like all onions, they are light feeders and do not normally need fertiliser. Take care with nitrogen-based fertilisers: too much nitrogen increases vegetative growth, which means that less bulb mass is formed. If necessary, a fertiliser containing potassium can be applied in spring. Potassium is also an important plant nutrient that helps plants maintain their water balance and makes the plants more resistant to disease and frost.
It is only necessary to water your walking onions during prolonged dry periods.
Especially in the beginning of their growth, you may need to remove weeds around the young tree onion plants.

Tip: Remove old and withered foliage regularly to give new stems enough space to grow. The onion fly (Delia antiqua) is a major pest of tree onions, its larvae feed on the underground parts of the plant. This can cause the stems to become unstable and bend over. Remove infested plants and find a new location to plant the tree onions.

How to propagate walking onions

In nature, tree onions propagate through the bulbs that are attached to the stems of the plant. At some point, the small bulbs are so heavy that the stem bends and the bulbs sink to the ground. There they take root, sprout and form new plants.
Since the tree onion does not produce flowers and seeds, it can only be propagated vegetatively – either by dividing the mother bulb or via the small bulbs. You can simply let nature take its course and let the plant reproduce itself, or you can harvest the bulbs and put them in the ground yourself. The best time for harvesting is August, when the bulbs are ripe and firm.
Another method of propagating bulbs is to divide the mother bulb. The plant forms several secondary bulbs while storing up reserves. Dig these up in autumn and plant them individually in new locations.

Are walking onions winter hardy?

Tree onions are a hardy perennial. This means that they can survive the winter in your veg patch and sprout again in the new year. If the winter is mild, the plant will even remain green and you can continue to harvest the spring onion-like stems.
Insulate potted tree onions to protect them from frost and also place them out of the wind.

Harvesting and using tree onions

All parts of the walking onion are edible. Not only the small bulbs and the green stems but also the mother bulbs in the soil. This means that at least part of the tree onion can be used almost all year round. Avoid harvesting the green stems excessively, especially if the plant is still to form the above ground bulbs. These small bulbs form between June and September and can be harvested as soon as they have reached the desired size. In autumn, from the end of September, harvest the remaining bulbs and use straight away or store them. In suitable conditions – cool, dark and above all very dry – these can be stored until the next spring. However, only onions that have not yet sprouted are suitable for storing.

In the kitchen, the small tree onions can be used in many ways. Because of their size, they are excellent for pickling but also great raw, fried or as an onion seasoning. Because of their finely aromatic, pungent and oniony taste, walking onions are also popular in pasta or as a side dish with meat and fish.
The green stems are an excellent substitute for chives and spring onions. In terms of nutrients, tree onions are in no way inferior to ordinary onions. As they contain essential oils, eating the bulbs can have a positive effect on vascular diseases such as arteriosclerosis and high blood pressure.

Summary: Harvesting and using Egyptian walking onions

• All parts of the tree onion can be used in the kitchen.
• Harvest the stems all year round once they have started sprouting and use them like spring onions or chives.
• The small onions are ready for harvesting from July and can be harvested for storage from the end of September. Tree onions can be used whole and pickled, fried or eaten raw in salads.

Tip: Do not remove all the bulbs on one stem in summer, but leave a few on the plant, as these will eventually form the next tier.

Do you like to experiment and grow unusual vegetables in your garden? Then read our article on curious vegetables.