Leeks (Allium porrum) refine stews, soups and stir-fries of all kinds with their spicy aroma. Once you have chosen the right varieties of the white-green vegetables, you can harvest them all year round. Whether summer leeks, autumn leeks or winter leeks
A vegetable for every season
Leeks are wonderful to plant in spring or summer – but you can harvest them almost any time. Even in winter, when the beds are noticeably empty, the leek remains sturdy and provides a vitamin-rich supply for the kitchen even at temperatures below zero.
It all depends on the right variety and good timing: The robust winter leek forms firm, dark green foliage and comes into the bed quite late. The summer and autumn varieties start earlier, are usually much more tender and more productive, but usually do not tolerate frosty temperatures.
Like onions and garlic, leeks belong to the genus Allium in the subfamily Allioideae, but they taste much milder than their pungent relatives. Unlike the field garlic (Allium ampeloprasum), which is native to the Mediterranean region and is probably the wild species, it does not form a bulb.
The characteristic stems of the biennial, herbaceous plant are composed of tubular lower leaves that form a false shoot. Of particular culinary interest are the lower, white stem areas, which are promoted by mounding. The upper leaves, on the other hand, appear flattened, which is why leeks are often called broad leeks.
Location and soil
Leeks thrive best in a sunny to semi-shady location. If the soil is also deeply loosened, well-drained and humus-rich, nothing stands in the way of successful cultivation. It is best to work mature compost or well-rotted manure into the soil. Green manure also provides good starting conditions.
You can grow summer leek varieties on the windowsill as early as January. The seeds need 20 to 25 °C during the germination phase – in the growing phase it should already be 17 to 20 °C to avoid shoots. Sow the autumn varieties in a cold frame from mid-March. Winter leek seeds are sown in the soil from April to mid-May – in May (after the Ice Saints) they also germinate directly outdoors. When the plants are as thick as a pencil, they move into their final location.
If you want to make things easy for yourself and prefer a mixed culture, sow directly between the rows of cabbage, carrots or celery in May. When the young plants have developed three leaves, they are thinned out.
Leek varieties for summer, autumn and winter
The bolt-resistant summer varieties 'Hilari' and 'Kulaures' are planted in March or April and can be harvested as early as late July. For May planting dates, autumn varieties such as 'Herbstriesen' or 'Shelton' are suitable and can remain in the bed from August to December. In July, plant the robust winter leek, for example 'Blaugrüner Winter' or 'Avano'. Harvesting begins in December and lasts until spring.
The early varieties can be planted out under a fleece from mid-March – in April the seedlings can already be planted outdoors without protection. Winter leeks should move into their final location by the end of July at the latest.
The seedlings are planted 15 to 20 centimetres apart in previously made 15 centimetre deep furrows (or holes in light soils). The row distance is at least 25 centimetres.
Do not close the holes immediately – watering well is sufficient for the plants to grow. Over the next few weeks, pile up the plants. Due to the lack of light in the soil and the lack of photosynthesis, the stems will get the coveted white stem – a principle that is also often used for asparagus.
Tip: To prevent the onion fly and leek moth from destroying the leeks from the inside, cover the leeks with a fine-meshed protective net immediately after planting. The netting also protects against late frosts, which can trigger flowering.
Prune leeks when planting
It is usually not necessary to shorten the roots when planting. If the roots are very long, prune them at most so that they do not bend when you plant them.
If the roots are weak or damaged, you can trim the foliage a little to ensure a good leaf-to-root ratio. In summer, shortening the foliage also has a beneficial effect on the water balance of the tender plants. In this way, the evaporation area is reduced in the early stages. However, you should not remove more than a third.
The perfectly bleached leek
To obtain a long, white stem, mound the leeks several times during the season with soil up to a height of about 25 centimetres. If there is not enough soil, you can pull kitchen paper rolls or black plastic tubes over the plants about 4 to 6 weeks before harvest.
Always make sure that the leaf axils are not covered with soil and thus no soil substrate trickles into the leaf rings – this facilitates later processing in the kitchen!
The hotter summers make it clear: leeks need even soil moisture to grow vigorously. Especially in the main growth phase from June to September, you should water additionally in case of persistent drought and on light sandy soils. This is because the leafy vegetables acknowledge a lack of water with slow growth and quite thin stems.
Straw or grass mulch keeps the urgently needed moisture well in the soil. In the first few weeks, the mulch layer also helps to suppress weeds. Straw mulch laid high even provides the desired bleaching effect.
A good supply of nutrients is also important: after basic fertilisation with compost or composted manure, the strong grower is always given an organic fertiliser, for example horn meal. Comfrey and nettle liquid manure also work quickly and reliably. They are best applied at weekly intervals. Be careful not to pour the liquid manure into the shoots!
Tip: If possible, winter-hardy varieties should not be repeatedly exposed to frosty temperatures. For this reason, mounding and covering with leaves and brushwood (or a fleece) is advantageous during the cold season.
When the stems have reached a diameter of 3 centimetres, you can harvest the leeks. Summer leeks should be taken out of the ground before the first frost at the latest, whereas winter leeks provide a fresh culinary treat even in the cold season. However, even hardy representatives should not end up in the kitchen too late, as they prepare for flowering in early spring – the first signs are hardening at the base.
As the plants are deep in the soil, care is needed when pulling them out – the shafts can easily break. It is best to first loosen the soil with a digging fork and then carefully lift the plants from below – this way they will remain intact when removed.
Tip: Harvesting is easy even when the ground is frozen if you spread a thick layer of autumn leaves in good time.
Harvesting leek seeds
A cold stimulus in winter causes the leeks to “shoot”. Finally, in the second year, a pretty ball of flowers appears that strongly resembles ornamental leeks. If there is no more space in the vegetable patch, the selected seed-bearing plants can also be moved to the border.