How to Grow Leek
'Blue Solaise' from Seed
The heritage French winter leek -- deep blue-green leaves that turn vivid blue-violet in cold weather; a 19th-century variety (Bleu de Solaise) that fills the hungry gap with harvests from February to April; sow modules from January; transplant pencil-sized seedlings using the dib-and-water technique; earth up progressively for white shanks; flavour sweetens dramatically after frost; ornamental enough for cottage garden borders
Leek 'Blue Solaise' (Bleu de Solaise) is a 19th-century French heritage variety that is simultaneously the most ornamentally beautiful leek available from seed and one of the finest winter vegetables a UK gardener can grow. The leaves are an extraordinary deep blue-green -- not the conventional grey-green of most leek varieties, but a genuinely blue-toned foliage that photographs strikingly and draws attention in the vegetable garden. But the distinctive quality that has made Blue Solaise famous is its cold response: as winter temperatures drop below freezing, the leaves deepen their colour further, turning from blue-green to a rich blue-violet that is unlike anything else in the winter garden. The deeper the frost, the more vivid the blue-purple colouration becomes.
The practical qualities match the ornamental ones. Blue Solaise is among the hardiest leeks available, reliably overwintering in even the coldest UK conditions and remaining harvestable throughout February, March, and April -- precisely the "hungry gap" period when most vegetable gardens are empty and shop-bought leeks are at their most expensive. The shanks are sweet and mild after frost exposure (the same starch-to-sugar conversion that improves kale also operates in leeks). At 40-50cm with thick, crisp shanks, this variety is exceptional in potato-leek soup, the French vichyssoise, sauteed with butter, or simply braised whole as a winter side dish of quiet brilliance.
Quick Facts at a Glance
Plant Type
Hardy biennial vegetable H7 -- 19th-century French heritage; ornamental and edible
Colour
Deep blue-green leaves turning vivid blue-purple in cold weather -- unique trait
Harvest
February-April (main); extremely hardy winter leek for the "hungry gap"
Sow
Modules January-April; transplant at pencil size; drop into dibbed holes, water, leave
Blanch
Earth up progressively as leeks grow to create long white shanks
Difficulty
2 out of 5 -- long season but reliable and very hardy
Understanding the Plant
The Colour Change -- Why Cold Turns Them Blue-Purple
The deep blue-violet colouration that develops on Blue Solaise leaves in cold weather is caused by the accumulation of anthocyanin pigments -- the same class of pigments that turn autumn leaves red and purple. In leeks, anthocyanin production is triggered by cold temperatures as a stress response; the pigments act as a kind of chemical antifreeze, lowering the freezing point of leaf cells and reducing frost damage. The deeper the cold, the more anthocyanin accumulates, and the more vivid the blue-purple colouration becomes. This colour is not merely ornamental -- it is a direct indicator of the cold-sweetening process that improves the leek's flavour for winter harvesting.
The Planting Technique -- Drop-and-Water, Never Firm
The traditional UK leek planting technique is simple and effective: use a dibber (a pointed wooden or metal tool) to make holes 15cm deep at 15-20cm spacing in prepared soil. Drop one pencil-sized seedling into each hole. Do NOT fill the hole with soil -- simply pour water into the hole. As the water settles, it pulls just enough fine soil around the roots to anchor the plant without burying the stem. As the leek grows, the hole gradually fills naturally and the stem is blanched white by the soil that surrounds it. This technique, known as "dibbing in", produces the long, well-blanched white shanks that make leeks so useful in the kitchen.
Ornamental Border Value
Blue Solaise is ornamental enough to grow in a cottage garden border alongside flowers -- the deep blue-green foliage and upright architectural form create a striking structural contrast to rounded, soft-textured flowering plants. In winter, when the blue-purple colour develops, the decorative quality becomes exceptional. Heritage vegetable gardeners have long known that the most beautiful kitchen gardens mix vegetables and flowers; Blue Solaise is a prime example of a vegetable that earns its place in both the productive and ornamental garden simultaneously.
Sowing & Growing On
Sow in Modules January-April -- Transplant When Pencil-Sized
Sow 2-3 seeds per module cell, 0.5-1cm deep, at 15-18°C. Thin to the strongest seedling when 2cm tall. Grow on at 12-15°C. Transplant when seedlings are pencil-sized (approximately 6 weeks from sowing) and 15-20cm tall. Use the dib-and-water planting technique for well-blanched shanks.
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Sow 2-3 seeds per module cell at 0.5-1cm deep, 15-18°C, January-April indoors. Germination in 7-14 days. Thin to one seedling per cell when 2cm tall. Grow on in cool, bright conditions. Leek seedlings are slow initially -- they take approximately 6-10 weeks from sowing to reach transplantable pencil-sized size.
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Transplant when seedlings are pencil-sized (about 1cm diameter) and 15-20cm tall. Trim the tops to 10cm and trim the roots slightly with scissors to encourage new root growth. Use a dibber to make holes 15cm deep at 15-20cm spacing in well-prepared, fertile soil. Drop one seedling per hole. Do not fill holes with soil.
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Water the holes -- the water fills them with sufficient fine soil to anchor the plants. Do not firm soil around the seedlings; this is not needed. Water regularly until established, then once a week in dry weather. Remove any weeds growing close to the leeks as they compete for the rich soil that leeks need.
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Earth up progressively as leeks grow to blanch the white shanks. Gently draw soil up around the base of each leek 2-3 times through the growing season to increase the length of the white, tender blanched shank. Avoid getting soil into the central heart of the leek -- tip the leaves gently to one side and work soil around the outside of the stem only.
Growing On & Care
In the Kitchen -- Winter Heritage Cooking
Blue Solaise is at its finest from November through to April -- the period when the leaves are at their most vivid blue-purple and the shanks have accumulated maximum sweetness from repeated frost exposure. The classic preparation is potato-leek soup: sweat the leeks gently in butter until soft, add diced floury potatoes and stock, simmer until tender, blitz or serve chunky. The same base recipe produces vichyssoise (chilled, cream-enriched) when made with summer leeks. Blue Solaise is also exceptional simply braised whole in butter with a splash of white wine, or thinly sliced raw in winter salads where the blue-purple colour provides dramatic visual contrast.
The Cold-Weather Flavour
Leeks, like kale, undergo the starch-to-sugar conversion in cold weather that improves flavour. The Blue Solaise leeks harvested in February and March after extended winter cold are noticeably sweeter and more complex in flavour than the same variety harvested in October or November before significant cold. The compound that produces this sweetness is fructooligosaccharides -- the same class of compounds that give onions their characteristic sweetness. Frost-kissed leeks harvested in late winter represent the vegetable at its absolute flavour peak.
In the Ornamental Border
Blue Solaise looks remarkable planted alongside winter-flowering or structural garden plants. The upright architectural form (40-50cm tall) and extraordinary blue-green-to-purple colour provides a structural vertical in the winter border that few ornamental plants can match at that time of year. Planted in groups of 5-7 alongside Hellebores, winter Cornus, or evergreen structural plants, the leek colonises its winter niche with genuine ornamental authority. Harvest progressively from outside inward to maintain the display for as long as possible.
Brassica Companion -- Leek Fly Deterrent
Leeks belong to the Allium family (not Brassica) and can actually be beneficial as companion plants near carrots -- the strong Allium scent masks the carrot's odour from carrot fly. Include leeks in your vegetable plot rotation separately from the brassica rotation. Leek rust (orange powdery patches on leaves) can affect Blue Solaise -- it is primarily cosmetic and rarely affects crop quality significantly, but removing and disposing of (not composting) affected leaves reduces spread. Leek moth can be problematic in some areas; covers of fine insect-proof netting from June provide the most effective protection.
Harvesting Technique
Harvest Blue Solaise leeks using a garden fork to loosen the soil around the roots before lifting -- pulling by the leaf often snaps the leek at soil level. Slide the fork in at an angle 10cm from the leek and lever gently to loosen the root system, then lift by the base. Leeks in the ground can remain usable throughout winter and into spring -- there is no rush to harvest the whole row at once. Harvest progressively as needed, leaving the remaining plants to continue developing and improving in colour and flavour.
The Hungry Gap Vegetable
The "hungry gap" -- the period from approximately late March to June when most stored vegetables have been used and new crops are not yet ready -- is one of the most challenging times in the UK kitchen garden calendar. Blue Solaise fills this gap: it is harvestable from February through to late April or even May if plants are left, providing fresh winter vegetables exactly when the garden is otherwise empty. The overlap between Blue Solaise harvest and the beginning of the spring growing season means there is a period in March when both are available simultaneously -- a brief abundance in what is usually the leanest time.
Sowing & Harvest Calendar
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| Sow modules (Jan-Apr) |
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| Transplant (Apr-Jun) |
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| Growing (summer-autumn) |
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| Colour deepens with frost |
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| Main harvest (Feb-Apr) |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
|---|---|---|
| Leek rust (orange patches on leaves) | Fungal disease; overcrowding | Remove affected leaves promptly and dispose of (do not compost). Ensure adequate spacing (15-20cm) for air circulation. Rust is primarily cosmetic and rarely affects crop quality significantly on robust varieties like Blue Solaise. |
| Leek moth damage (longitudinal tracks in leaves) | Leek moth larvae | Cover plants with fine insect-proof netting from June to prevent egg-laying. Remove affected outer leaves during harvest. In most UK areas leek moth is absent or sporadic; it is more common in southern England. |
| Short white shanks | Insufficient earthing up; planted too shallowly | Earth up the stem progressively 2-3 times through the growing season to build a long white shank. The dib-and-water planting technique (15cm deep holes) provides the initial blanching depth; earthing up extends it further as the plant grows. |
| Slow establishment after transplanting | Seedlings too large; root damage | Transplant when pencil-sized (1cm diameter) -- seedlings transplanted too large suffer more root damage and check more severely. Trim roots slightly before transplanting to encourage new root growth. The dib-and-water technique is gentler on roots than firming soil around the stem. |
Plant Specifications
The blue-purple winter leek that fills the hungry gap -- sweet, frost-kissed, and uniquely beautiful in cold weather
Sow modules from January at 15-18°C. Grow on until pencil-sized (6-10 weeks). Transplant using a dibber: make holes 15cm deep, drop one seedling per hole, water in, leave. Earth up the stems 2-3 times as they grow for long white shanks. Watch the leaves deepen from blue-green to vivid blue-violet as winter cold arrives. Harvest the sweetest leeks of the year through February, March, and April.
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