Pearl onion

You plant pearl onions from late summer to autumn and let them overwinter in the ground. They are quite frost-hardy and sprout again in spring. In severe frosts without snow cover or frequent alternation of frost and thaw, cover the bed with a little brushwood or leaves, and harvest only when the foliage begins to wilt.

Pearl onions (Allium ampeloprasum var. sectivum, the true pearl leek) are propagated most safely, and true to type, by their bulblets (daughter bulbs): the plant forms several small bulblets underground. When the foliage wilts around 1 July, lift the clump and separate the small daughter bulbs from the mother bulb. Let them dry further for a few days in an airy, shady place, then from September to December at the latest insert them into loose, sandy, humus-rich, well-drained soil: spacing in the row about 3 to 4 cm (small bulblets) to around 10 cm (larger ones), row spacing 15 to 20 cm, only a few centimetres deep. The bulblets sprout quickly, overwinter in the ground as green leek and in the following year, from early July, yield ripe pearl onions again. Bulblets are the reliable, true-to-type method for heritage varieties.

The true pearl leek can be grown from seed only to a limited extent: it does form a spherical flower head with viable seed, but this happens in the garden only exceptionally, because the flower stalk usually wilts or is cut off before seed ripens. If you want to try, let a plant flower and set seed and sow the seeds shallowly (1 to 2 cm) outdoors from mid-March; germination takes about two to three weeks at 10 to 20 °C. Plants raised from seed take considerably longer to reach harvestable size than those raised from bulblets. Caution when buying seed: much of what is sold as “pearl onion” (e.g. ‘De Barletta’ or ‘Weiße Königin’) is botanically Allium cepa (related to the bulb onion) and not the perennial pearl leek; it produces similar small pickling onions, but is a different species and does not form overwintering bulblet clumps.