Leek seed buying and growing guide

Grow Large American Flag Leeks

Large American Flag is a traditional leek variety grown for its substantial white stems, upright blue-green foliage and mild onion-like flavour. It develops slowly through cool conditions and can remain in the garden until required, providing a useful extended harvest period.

Seedmart supplies Large American Flag leek seeds for home gardens, raised beds, containers, market gardens and commercial vegetable production throughout Australia. The variety is open pollinated, untreated and suited to growers seeking dependable winter and cool-season leek production.

For the longest white stems, transplant seedlings into shallow trenches or gradually draw soil around the lower plant as it grows. Harvest young leeks for fine tender stems or allow plants to mature for thick stalks suited to soups, roasts, pies, sauces and slow-cooked dishes.

Why Grow Large American Flag Leeks?

Hardy Cool-Season Crop

Large American Flag tolerates cold conditions and is well suited to autumn, winter and spring vegetable production.

Thick White Stems

The variety produces substantial elongated bases that can reach approximately 5 cm in diameter under favourable conditions.

Mild Onion-Like Flavour

Leeks provide a softer, sweeter allium flavour than many mature bulb onions.

Extended Harvest Window

Mature plants can remain in suitable garden soil and be harvested progressively as required.

Suitable for Deep Containers

Leeks can be grown in tubs, raised planters and deep pots where soil, moisture and spacing are adequate.

Packet and Larger Quantities

Choose smaller packs for household planting or larger quantities for repeated and market-garden sowings.

What Is a Leek?

A leek is a member of the allium family grown for its long white and pale-green leaf bases. It is closely related to onion, garlic, shallot, spring onion and chives.

Unlike a bulb onion, a leek does not normally form a distinct rounded bulb. Its overlapping leaf sheaths create an elongated cylindrical stem-like base.

Leek plants generally produce:

White Blanched Bases

The tender lower portion develops where light is excluded by soil, close spacing or another blanching method.

Pale-Green Inner Leaves

The central green section is tender enough for slicing, sautéing and general cooking.

Dark Blue-Green Foliage

The upper leaves are firmer and strongly flavoured but remain useful in stocks and long-cooked dishes.

Flowering Stems

Plants retained through their reproductive cycle produce tall stems with rounded allium flower heads and mature seed.

The familiar leek stem is formed from overlapping leaf bases. Hilling or trench planting excludes light and increases the length of the pale edible section.

What Is Large American Flag Leek?

Large American Flag is a traditional open-pollinated leek known for thick white stems, upright foliage, cold tolerance and dependable winter production.

It is suitable for:

  • Full-sized mature leeks
  • Young or baby leek harvesting
  • Autumn and winter vegetable gardens
  • Soups, stocks and stews
  • Roasting, braising and sautéing
  • Fresh-market bunches
  • Seed saving where adequate isolation is maintained

Under suitable conditions, plants commonly grow approximately 30–50 cm high and can develop substantial stems.

Large American Flag is the variety currently offered in this category. The page should focus on its actual characteristics rather than presenting unavailable leek varieties as part of the Seedmart range.

Leeks vs Onions

Leeks and onions are related alliums but produce different harvest structures and culinary results.

Leeks Bulb Onions
Produce elongated overlapping leaf bases. Produce a rounded underground or partly exposed bulb.
Have a mild, sweet and gently onion-like flavour. Flavour ranges from sweet and mild to strong and pungent.
Require hilling or trenching for a long white section. Bulbs generally need room to expand near the soil surface.
Commonly used in soups, pies, braises and sauces. Used raw, fried, roasted, pickled and cooked across many dishes.
Can remain in cool garden soil until required. Mature storage onions are commonly cured after harvest.
Do not normally form a substantial round bulb. Bulb formation is a principal production objective.

Leeks vs Spring Onions

Leeks and spring onions can look similar while young, but they differ in size, texture and maturity.

Leeks Spring Onions
Develop broad, flat or folded leaves. Generally develop narrow, hollow or tubular leaves.
Produce thick cylindrical white bases. Produce slender white stems or small immature bulbs.
Require a long growing period. Are commonly harvested much earlier.
Usually cooked, especially when mature. Frequently eaten raw or lightly cooked.
Have a mild, substantial onion flavour. Have a fresh, sharper onion flavour.
Need wider mature spacing. Can be grown relatively close together.

Leeks vs Shallots

Leeks and shallots belong to the allium group but are grown for different plant parts.

Leeks Shallots
Harvested for elongated white leaf bases. Harvested for small clustered or individual bulbs.
Have a soft, mild onion flavour. Have a concentrated flavour combining onion and garlic-like qualities.
Usually used fresh after lifting. Bulbs may be cured and stored.
Can be harvested young or mature. Generally harvested once bulbs mature.
Require blanching for the longest white section. Do not require stem blanching.

What Part of a Leek Do You Eat?

The white base and pale-green inner section are the most tender and commonly used parts of a leek.

The darker green leaves are firmer and more fibrous but are still useful for flavouring stocks, broths, soups and long-cooked dishes.

Leek Part Texture and Flavour Suitable Uses
White base Tender, mild and slightly sweet Sautéing, roasting, soups, pies, sauces and gratins.
Pale-green section Moderately tender with a fuller leek flavour General cooking, frying, stews and braised dishes.
Dark-green leaves Firm, fibrous and strongly flavoured Stocks, broths, bouquet garni and long cooking.
Young whole leek Fine, tender and mild Roasting, grilling, steaming and whole-vegetable presentation.
Flower stalk Becomes firm as flowering progresses Young tender portions may be cooked, but mature stems reduce market quality.
Most of the leek is usable. Remove the roots and damaged leaf tips, then reserve clean dark-green foliage for stock rather than automatically discarding it.

What Do Leeks Taste Like?

Leeks have a mild allium flavour that is generally sweeter, softer and less pungent than mature bulb onion.

White Base

Mild and Sweet

The blanched lower section has the softest flavour and most tender texture.

Pale Green

Fresh and Onion-Like

The middle section provides greater flavour while remaining suitable for most recipes.

Dark Leaves

Strong and Herbaceous

Upper foliage has a fuller allium flavour and requires longer cooking.

Young Leeks

Delicate and Tender

Baby leeks can be cooked whole or sliced with minimal trimming.

Roasted

Sweet and Caramelised

Dry heat concentrates the natural sweetness of the white and pale-green sections.

Slow-Cooked

Soft and Savoury

Leeks break down into a silky base for soups, sauces and braised dishes.

Can Leeks Be Eaten Raw?

Yes. Young or finely sliced leek can be eaten raw, although its texture is firmer than spring onion and its flavour can remain relatively strong.

Raw leek is best taken from the white or pale-green section and sliced thinly.

Potential raw uses include:

  • Finely sliced salads
  • Slaws
  • Sandwiches and wraps
  • Fresh garnishes
  • Potato salad
  • Soft-cheese mixtures
  • Dressings and relishes

Mature dark-green leaves are generally better suited to cooking.

How to Grow Leeks in Australia

Leeks are long-season alliums requiring fertile free-draining soil, consistent moisture and cool to mild growing conditions.

Begin with Strong Seedlings

Raise leeks in trays or nursery rows before transplanting them into their final spacing.

Prepare Deep Fertile Soil

Loose soil allows roots to develop and makes trenching, hilling and harvest easier.

Maintain Steady Moisture

Regular watering supports continuous stem thickening and reduces tough, interrupted growth.

Blanch the Lower Stem

Exclude light gradually to increase the length of the tender white portion.

Leeks require patience. Large American Flag is a slow-maturing crop, but healthy plants provide substantial stems and a flexible harvest period.

When to Plant Leeks in Australia

Leek sowing periods vary by climate. In subtropical regions, they are generally grown through the cooler months, while cool and temperate regions have a broader planting window.

Climate Zone General Sowing Period Growing Notes
Cool September to March Raise crops from spring through early autumn and allow mature plants to develop during cool conditions.
Temperate September to February Spring, summer and early autumn sowing can provide autumn through spring harvests.
Subtropical April to July Use the cooler part of the year for the most reliable stem growth.
Tropical Generally not recommended Persistent warmth and humidity can make high-quality mature leek production difficult.
Arid March to May Provide reliable irrigation and protection from hot drying winds.

These planting periods are general guides. Local frost, elevation, heat, humidity, soil conditions and irrigation availability should also be considered.

When to Plant Leeks in Australian States and Cities

Location General Planting Guide Key Considerations
Brisbane and South East Queensland April to July Grow through autumn, winter and early spring before severe heat returns.
Sydney and coastal New South Wales February to September Autumn and winter crops are reliable where drainage and airflow remain adequate.
Inland New South Wales February to August Protect small seedlings from severe frost and maintain irrigation during dry weather.
Melbourne and Victoria September to March A broad cool-season window supports autumn, winter and spring harvests.
Canberra and cool inland districts September to February Raise seedlings through mild conditions and allow mature plants to stand through winter.
Adelaide and South Australia March to August Maintain moisture during dry autumn and spring weather.
Perth and south-west Western Australia March to August The climate can suit cool-season leek production, although this product is currently restricted from shipment to Western Australia.
Tasmania September to March The cool climate is suitable for leeks, although this product is currently restricted from shipment to Tasmania.
Darwin and tropical northern Australia Generally not recommended Persistent tropical warmth can reduce stem quality and make long-season production difficult.

How to Grow Leeks from Seed

Large American Flag leeks can be direct-sown, but they are commonly raised in trays or nursery beds before transplanting.

  1. Choose the appropriate sowing period.
    Plan the crop so most stem development occurs through cool to mild weather.
  2. Prepare a fine seed-raising medium.
    Use a clean mix that retains moisture while draining freely.
  3. Sow shallowly.
    Plant the seed approximately 5–10 mm deep.
  4. Maintain consistent moisture.
    Do not allow the fine seedbed or young seedlings to dry completely.
  5. Provide strong light.
    Bright conditions produce sturdy seedlings rather than weak elongated growth.
  6. Allow seedlings to develop.
    Raise them for approximately eight to ten weeks or until they are strong enough to transplant.
  7. Harden plants gradually.
    Introduce seedlings progressively to outdoor conditions.
  8. Transplant into trenches or planting holes.
    Position plants according to the intended blanching system.
  9. Maintain water and nutrition.
    Support uninterrupted growth throughout the long production period.
  10. Hill progressively.
    Draw soil around the lower stems as plants grow without burying the central leaves.
Do not rush the seedling stage. Strong, pencil-thick transplants generally establish more reliably than weak or severely root-bound seedlings.

How Deep Should Leek Seeds Be Planted?

Plant Large American Flag leek seeds approximately 5–10 mm deep.

Seedling Trays

Use a fine, free-draining seed-raising medium.

  • Sow approximately 5–10 mm deep
  • Cover lightly
  • Water with a gentle spray
  • Provide strong light after emergence

Direct Sowing

Sow into fine, weed-free soil where plants can establish without heavy competition.

  • Prepare a level seedbed
  • Sow in shallow drills
  • Maintain even moisture
  • Thin seedlings to final spacing

How Long Do Leek Seeds Take to Germinate?

Large American Flag leek seeds commonly germinate within approximately 14–21 days under suitable conditions.

Soil Temperature

An approximate soil-temperature range of 18–23°C supports reliable germination.

Moisture

Keep the seedbed evenly moist without leaving it waterlogged.

Sowing Depth

Deeply buried seed can emerge slowly or fail to reach the surface.

Seedling Light

Bright light after emergence helps produce sturdy, upright plants.

Can Leek Seedlings Be Transplanted?

Yes. Transplanting is a standard leek-production method and makes it easier to create long blanched stems.

Seedlings are commonly transplanted after approximately eight to ten weeks.

When transplanting:

  • Choose healthy upright seedlings
  • Harden them gradually
  • Water the nursery area before lifting
  • Keep roots moist during handling
  • Place plants into trenches or deep planting holes
  • Water them into position
  • Avoid filling deep holes completely with soil immediately

How Deep Should Leek Seedlings Be Transplanted?

Leek seedlings can be placed into holes or shallow trenches approximately 10–15 cm deep to encourage a longer pale section.

The plant should remain upright, with the youngest central leaves above the soil.

A common planting method is to:

  1. Create a deep narrow hole.
    Use a dibber or similar tool.
  2. Lower the seedling into the hole.
    Keep the roots positioned downwards.
  3. Leave the hole partly open.
    Do not tightly pack soil around the stem.
  4. Water into the hole.
    Water settles soil gently around the roots.
  5. Allow soil to fill gradually.
    Rain, irrigation and cultivation progressively close the hole.
Do not bury the central growing point. Soil should cover the lower stem gradually while the active leaves remain exposed.

How Far Apart Should Leeks Be Planted?

Spacing influences stem diameter, plant population and airflow.

Production Goal Approximate Plant Spacing General Result
Baby leeks Approximately 5–10 cm Produces finer stems for early whole-plant harvest.
Standard mature leeks Approximately 15–20 cm Provides room for substantial stem development.
Large individual plants Approximately 20–25 cm Encourages thicker stems and easier harvest access.
Row spacing Approximately 30–45 cm Allows room for weeding, hilling and harvesting.
Commercial production Adjusted to target grade Plant density should match required stem diameter and bunch specification.

Can Leeks Be Grown in Pots?

Yes. Leeks can be grown in deep containers where soil volume, spacing and moisture are adequate.

Container Requirements

Choose a deep pot, tub or raised planter.

  • Allow approximately 30 cm of soil depth or more
  • Provide unrestricted drainage holes
  • Use fertile, moisture-retentive potting mix
  • Space plants according to required stem size

Container Management

Potted leeks can dry more rapidly than garden-grown plants.

  • Check moisture regularly
  • Feed during the long growing period
  • Add potting mix gradually around the stems
  • Protect containers from severe drying winds

Do Leeks Need Full Sun?

Leeks generally perform best in full sun but tolerate light partial shade.

Provide at least approximately six hours of direct sunlight for strong stem growth.

Heavy shade may result in:

  • Thin elongated foliage
  • Slow stem thickening
  • Pale weak plants
  • Reduced harvest weight
  • Extended periods of wet foliage

Light afternoon shade can be useful where young plants are exposed to severe heat.

What Soil Do Leeks Need?

Leeks prefer fertile, loose and free-draining soil with a pH of approximately 6–7.

Suitable preparation may include:

  • Incorporating well-decomposed organic matter
  • Breaking up compacted soil
  • Removing stones and persistent weeds
  • Preparing trenches where long white stems are required
  • Applying balanced fertility
  • Maintaining good drainage

Avoid placing fresh concentrated manure directly around young roots.

Watering and Feeding Leeks

Leeks require consistent moisture throughout their long growing period.

Water deeply enough to maintain active root growth without leaving the soil continually saturated.

Large American Flag generally benefits from:

  • Balanced fertility before planting
  • Adequate nitrogen during leaf and stem growth
  • Regular moisture during dry weather
  • Mulch between rows
  • Additional feeding during extended production
  • Good drainage during prolonged rain
Interrupted growth reduces stem quality. Repeated drought, severe weed competition and nutrient stress can produce thin or tough leeks.

How to Blanch Leeks

Blanching excludes light from the lower stem, preventing chlorophyll development and creating a longer white section.

Trench Planting

Plant seedlings in a shallow trench and gradually fill it as the plants grow.

Deep Planting Holes

Place seedlings into narrow holes that fill naturally through watering and cultivation.

Progressive Hilling

Draw loose soil around the stems several times during the growing season.

Collars or Sleeves

Use suitable barriers around the lower stems to exclude light without adding soil between the leaves.

When hilling:

  • Wait until plants are established
  • Add soil gradually rather than all at once
  • Keep soil out of the central leaf fan
  • Avoid burying wet or diseased foliage
  • Maintain good drainage
  • Stop before the central growing point is covered

Why Do Leeks Need Blanching?

Blanching is not essential for plant survival, but it improves the culinary quality and market appearance of the lower stem.

Blanched sections are generally:

  • Paler in colour
  • More tender
  • Milder in flavour
  • Easier to slice
  • More familiar to retail customers
  • Suitable for standard bunch grading

Unblanched green portions remain edible but have a firmer texture and stronger flavour.

How Long Do Leeks Take to Grow?

Large American Flag leeks commonly require approximately 120–150 days from sowing to mature harvest.

Growth Stage Typical Period General Characteristics
Germination Approximately 14–21 days Seedlings emerge as fine upright green shoots.
Transplant stage Approximately 8–10 weeks Seedlings are moved into trenches, rows or final containers.
Baby leek harvest Approximately 70–100 days Fine young stems harvested before full diameter develops.
Mature Large American Flag Approximately 120–150 days Substantial white and pale-green stems suitable for full harvest.
Flower and seed production Longer than the vegetable harvest period Selected plants complete a biennial reproductive cycle.

Maturity varies with temperature, transplant age, spacing, soil fertility, moisture and target stem diameter.

When to Harvest Leeks

Leeks can be harvested at several stages.

Young leeks are tender and mild, while mature Large American Flag plants provide thicker stems and greater harvest weight.

Signs of maturity include:

  • Stems have reached the required diameter
  • The lower section is firm and upright
  • Plants display healthy blue-green foliage
  • The blanched section has reached a useful length
  • Plants have not developed a mature flower stem
  • Outer leaves remain sound enough for handling

How to Harvest Leeks

Loosen the soil before lifting mature leeks. Pulling directly from compacted ground can snap the stem or leave roots behind.

  1. Water dry soil beforehand.
    Moist soil is easier to loosen than hard dry ground.
  2. Insert a garden fork beside the plant.
    Avoid piercing the stem.
  3. Lift the root zone.
    Loosen soil beneath and around the leek.
  4. Pull the plant gently.
    Hold the base rather than the upper leaves.
  5. Shake off loose soil.
    Avoid forcing soil deeper between the leaves.
  6. Trim for the intended use.
    Remove roots and damaged foliage after harvest.

Can Leeks Stay in the Ground After Maturity?

Yes. Mature leeks can remain in cool, well-drained soil and be harvested as required.

Leaving them in the ground can provide convenient garden storage, but quality may decline where plants experience:

  • Waterlogging
  • Severe heat
  • Rust or other leaf disease
  • Thrip damage
  • Flowering
  • Repeated freeze and thaw conditions
  • Excessive stem splitting

Harvest before conditions cause significant deterioration.

Do Leeks Regrow After Cutting?

A leek base can produce new green growth where the basal plate and roots remain alive.

Regrowth is generally smaller than the original plant and should not be expected to produce an identical second commercial stem.

For experimental regrowth:

  • Retain several centimetres of the basal section
  • Keep the root plate intact
  • Place the base in shallow water temporarily
  • Transfer it into soil after new growth begins
  • Maintain moisture
  • Harvest the regrowth while young

Seed-grown plants provide stronger roots, predictable variety identity and full-sized production.

How to Clean and Prepare Leeks

Soil can collect between leek leaves as the stems are blanched. Thorough cleaning is therefore essential.

  1. Trim the roots.
    Remove the basal roots without cutting away excessive white stem.
  2. Remove damaged foliage.
    Discard yellow, split or severely damaged leaves.
  3. Cut the leek lengthwise.
    Split the stem from the pale-green end towards the base.
  4. Separate the layers.
    Open the leaves so trapped soil becomes visible.
  5. Rinse thoroughly.
    Wash under clean running water or in a bowl of clean water.
  6. Drain well.
    Remove excess moisture before frying or roasting.
  7. Slice for the recipe.
    Cut into rings, half-moons, strips or larger sections.

How to Cut and Slice Leeks

The best cutting method depends on the intended dish.

Cutting Method How to Prepare It Suitable Uses
Thin rings Slice the cleaned white and pale-green stem across its width. Soups, sautés, omelettes and sauces.
Half-moons Split the leek lengthwise, then slice across each half. Pies, stews, frying and braising.
Long strips Cut cleaned sections lengthwise into narrow pieces. Stir-fries, garnishes and vegetable mixtures.
Large sections Cut young or mature leeks into substantial lengths. Roasting, grilling and braising.
Dark-green leaf pieces Wash thoroughly and cut into manageable sections. Stocks, broths and long-cooked dishes.

How to Cook Leeks

Leeks can be cooked quickly for texture or slowly until soft and sweet.

Sautéed

Soft Sliced Leeks

Cook rings or half-moons gently in oil or butter until tender without excessive browning.

Roasted

Sweet Caramelised Leeks

Roast larger sections until soft, browned and concentrated in flavour.

Soups

Classic Savoury Base

Use leeks in potato soup, vegetable soup, broth and creamy pureed dishes.

Braised

Tender Whole Sections

Cook slowly with stock, herbs, wine or sauce until the layers soften.

Pies

Mild Allium Filling

Combine cooked leeks with potato, chicken, fish, cheese, mushrooms or other vegetables.

Stir-Fried

Fine Leek Strips

Cook narrow slices briefly with other vegetables, noodles, meat or tofu.

How Long Should Leeks Be Cooked?

Cooking time depends on the cut size, maturity and required texture.

Cooking Method General Cooking Period Desired Result
Sautéing Approximately 8–15 minutes Soft slices with mild sweetness.
Steaming Approximately 8–15 minutes Tender young or medium-sized sections.
Boiling Approximately 10–20 minutes Soft leeks for purees, soups or further cooking.
Roasting Approximately 25–40 minutes Browned edges and soft interiors.
Braising Approximately 25–45 minutes Very tender whole or halved leeks.
Stock According to the stock recipe Flavour extracted from firm green leaves and trimmings.

Cooking periods are general guides. The age, thickness and size of the leek pieces will affect the time required.

How to Store Fresh Leeks

Freshly harvested leeks should be cooled and protected from dehydration.

For household storage:

  • Remove loose soil
  • Trim damaged leaves
  • Leave sound roots attached for short-term storage where practical
  • Refrigerate in a suitable produce bag or container
  • Avoid tightly sealing wet unwashed leeks
  • Wash thoroughly before cooking
  • Discard slimy, mouldy or unpleasant-smelling material

Uncut leeks generally store better than heavily trimmed or sliced stems.

Can Leeks Be Frozen?

Yes. Leeks can be frozen for later cooked use.

For freezing:

  1. Clean thoroughly.
    Remove all trapped soil from between the layers.
  2. Trim and slice.
    Prepare rings, half-moons or recipe-sized pieces.
  3. Blanch where preferred.
    Brief blanching can help preserve colour and storage quality.
  4. Cool rapidly.
    Transfer blanched pieces into cold water.
  5. Drain thoroughly.
    Remove excess surface moisture.
  6. Freeze in portions.
    Use suitable freezer-safe containers or bags.

Frozen leeks are best used in:

  • Soups
  • Stews
  • Pies
  • Sauces
  • Stocks
  • Cooked fillings

Can Leeks Be Grown as Microgreens?

Leeks can be grown as microgreens using untreated seed suitable for edible seedling production.

Leek microgreens generally have fine green leaves and a mild allium flavour.

They require:

  • A clean growing medium
  • Even seed distribution
  • Consistent moisture
  • Patience during germination
  • Bright light after emergence
  • Good airflow
  • Careful cutting because of their fine upright leaves
Use only untreated seed for edible shoots. Chemically treated seed must not be used for sprouts, microgreens or direct food consumption.

Do Leeks Flower or Bolt?

Leeks are botanically biennial and can produce a flower stem after sufficient maturity and cold exposure.

Bolting may be encouraged by:

Plant Maturity

Older plants naturally progress towards reproduction.

Cold Exposure

A prolonged cold period can prepare mature plants to flower.

Rising Temperatures

Warmer conditions and increasing day length support flower-stem development.

Plant Stress

Drought, root restriction and interrupted growth can reduce vegetable quality.

Once a firm flower stem develops, the leek becomes less suitable for standard fresh-market sale.

Common Leek Growing Problems

Poor Germination

Dry seedbeds, deep sowing, waterlogging and unsuitable temperatures can reduce emergence.

Thin Stems

Crowding, insufficient fertility, drought and inadequate growing time can limit diameter.

Short White Sections

Shallow planting and inadequate hilling reduce blanching length.

Rust-Coloured Spots

Allium rust can produce orange or brown pustules on foliage.

Silvery Leaf Damage

Thrips can scar leaves and reduce plant vigour.

Premature Flowering

Plant maturity, cold exposure and environmental stress can trigger bolting.

How to Manage Leek Rust and Thrips

Leeks can be affected by allium rust and thrips, particularly where crops remain dense or stressed.

Management practices include:

  • Maintaining adequate spacing
  • Improving airflow
  • Avoiding continual overhead irrigation late in the day
  • Removing severely affected foliage
  • Controlling volunteer alliums
  • Rotating onion-family crops
  • Maintaining steady plant growth
  • Using only legally registered crop-protection products according to their labels

What to Plant with Leeks

Leeks can share beds with cool-season vegetables that have compatible moisture and spacing requirements.

Potential neighbouring crops include:

  • Carrots
  • Beetroot
  • Celery
  • Lettuce
  • Spinach
  • Silverbeet
  • Brassicas
  • Radish as an early crop
  • Herbs and flowers supporting beneficial insects

Avoid placing leeks beside crops that will heavily shade them or interfere with hilling and harvest.

Can Leek Seed Be Saved?

Yes. Large American Flag is open pollinated and can produce seed where selected plants complete their biennial cycle.

To save leek seed:

  1. Select healthy plants.
    Retain vigorous specimens with desirable stem length and diameter.
  2. Allow plants to overwinter.
    Protect the selected leeks from severe damage.
  3. Permit flowering.
    The plants produce tall stems with round allium flower heads.
  4. Support pollination.
    Insects transfer pollen between flowers and plants.
  5. Allow seed heads to mature.
    Wait until capsules begin drying and dark seed becomes visible.
  6. Harvest before excessive shedding.
    Cut mature heads and finish drying them under cover.
  7. Clean and store.
    Remove dry plant debris and keep the seed cool and dry.

Will Leeks Cross with Onions?

Leeks generally do not cross with ordinary bulb onions because they belong to different allium species.

Different leek varieties can cross with one another when flowering at the same time. Leeks may also cross with compatible forms of Allium ampeloprasum.

Crossing does not change the edible stems of the current crop. It affects the characteristics of saved seed.

Growers saving Large American Flag true to type should isolate flowering plants from compatible leek varieties.

Packet and Larger-Quantity Leek Seeds

Home and Small-Scale Growers

Smaller quantities suit household gardens, raised beds and container growers trialling leeks for the first time.

  • Grow young or mature leeks
  • Harvest progressively through cool weather
  • Use trench or deep-hole transplanting
  • Grow untreated open-pollinated seed

Market Gardens and Commercial Growers

Larger quantities support scheduled fresh-market and bunching production.

  • Available in 10 g, 100 g and 250 g quantities
  • Suitable for repeated seasonal sowings
  • Useful for full-sized and baby-leek markets
  • Compare stem diameter, blanch length and harvest labour
Compare value by saleable stem production. Germination, transplant survival, plant density, white-stem length, stem diameter, cleaning labour and marketable yield all influence the actual production cost.

Important Considerations for Commercial Growers

Commercial leek production requires uniform seedlings, consistent blanching and a defined stem specification.

Seedling Uniformity

Even emergence and transplant size support consistent maturity and grading.

Stem Diameter

Plant spacing and harvest timing influence whether leeks grade as baby, standard or large stems.

Blanched Length

Trenching, planting depth and hilling determine the length of the white marketable section.

Crop Duration

A 120–150-day crop requires long-term weed, water and fertility management.

Cleaning Labour

Soil trapped between leaves can increase washing and trimming requirements.

Post-Harvest Cooling

Fresh leeks should be cooled promptly and protected from dehydration after lifting.

Conduct local production trials before large sowings. Germination, transplant survival, rust pressure, stem diameter, blanch length and maturity can vary with climate, spacing, soil and crop management.

Frequently Asked Questions

What is a leek?

A leek is a cool-season allium grown for its elongated white and pale-green leaf bases.

What is Large American Flag leek?

Large American Flag is an open-pollinated heirloom leek producing thick white stems, upright foliage and mild onion-like flavour.

Are leeks onions?

Leeks and onions are related alliums, but leeks produce elongated leaf bases rather than a rounded bulb.

Are leeks the same as spring onions?

No. Spring onions are slender and fast-growing, while leeks develop much thicker stems over a longer growing period.

What part of a leek do you eat?

The white and pale-green sections are the most tender. Clean dark-green leaves can also be used in stocks and long-cooked dishes.

Can you eat the green part of a leek?

Yes. The dark-green leaves are edible but firmer and more strongly flavoured than the white stem.

What do leeks taste like?

Leeks have a mild, slightly sweet onion-like flavour that becomes softer and sweeter after cooking.

Can leeks be eaten raw?

Yes. Finely sliced young white and pale-green leek can be used raw in salads, slaws and garnishes.

How do you grow leeks from seed?

Sow approximately 5–10 mm deep, raise strong seedlings and transplant them into trenches or deep planting holes.

When should leeks be planted in Australia?

Cool and temperate growers can sow from spring through early autumn. Subtropical growers generally sow from April to July.

When should leeks be planted in Brisbane?

Around Brisbane, Large American Flag leeks are generally best sown from April to July.

When should leeks be planted in Melbourne?

Around Melbourne, leeks can generally be sown from September through March.

How deep should leek seeds be planted?

Plant Large American Flag leek seeds approximately 5–10 mm deep.

How long do leek seeds take to germinate?

Large American Flag leek seeds commonly germinate within approximately 14–21 days.

What temperature do leek seeds need to germinate?

An approximate soil-temperature range of 18–23°C supports reliable germination.

Can leek seedlings be transplanted?

Yes. Leeks are commonly transplanted after approximately eight to ten weeks.

How deep should leek seedlings be planted?

Seedlings can be placed in holes or trenches approximately 10–15 cm deep while keeping the central leaves above the soil.

How far apart should leeks be planted?

Large American Flag leeks are generally spaced approximately 15–20 cm apart, with closer spacing used for baby leeks.

Can leeks be grown in pots?

Yes. Use a deep container with fertile potting mix, good drainage and consistent moisture.

Do leeks need full sun?

Leeks generally perform best in full sun but tolerate light partial shade.

How often should leeks be watered?

Water often enough to maintain consistent root-zone moisture. Frequency depends on soil, weather and plant size.

Why are my leeks thin?

Crowding, drought, poor fertility, weeds and insufficient growing time can limit stem diameter.

Why do leeks need blanching?

Blanching excludes light from the lower stem, creating a longer pale section with milder flavour and softer texture.

How do you blanch leeks?

Plant in trenches or deep holes and gradually hill soil around the lower stems while leaving the central leaves exposed.

How long do leeks take to grow?

Large American Flag commonly requires approximately 120–150 days from sowing to mature harvest.

When should leeks be harvested?

Harvest once the stems reach the preferred diameter and blanch length, before mature flower stems develop.

How do you harvest leeks?

Loosen the soil with a garden fork and lift the plant gently from the base.

Can leeks stay in the ground after maturity?

Yes. They can remain in cool, well-drained soil and be harvested progressively while quality remains acceptable.

Do leeks regrow after cutting?

The basal plate can produce new green growth, although the regrown plant is generally smaller than the original leek.

How do you clean leeks?

Split the leek lengthwise, separate the layers and rinse thoroughly to remove soil trapped between the leaves.

How do you cut leeks?

Remove the roots and damaged leaves, clean the stem and slice it into rings, half-moons, strips or larger sections.

How do you cook leeks?

Leeks can be sautéed, roasted, steamed, boiled, braised or added to soups, pies and sauces.

How long should leeks be cooked?

Thin slices may soften within 8–15 minutes, while large roasted or braised sections can require 25–45 minutes.

Can leeks be frozen?

Yes. Clean, slice and freeze leeks for later use in soups, stews, pies and sauces.

How should fresh leeks be stored?

Refrigerate uncut leeks in a suitable produce bag or container and protect them from dehydration.

Can leeks be grown as microgreens?

Yes, using untreated seed suitable for edible microgreen production.

Do leeks flower?

Yes. Mature leeks can produce tall allium flower stems after cold exposure and seasonal change.

Why are there orange spots on leek leaves?

Orange or brown pustules can indicate allium rust, particularly where foliage remains damp or crops are densely planted.

What can be planted with leeks?

Leeks can share beds with carrots, beetroot, celery, lettuce, spinach, brassicas, radish and selected herbs.

Can Large American Flag leek seed be saved?

Yes. Large American Flag is open pollinated. Allow selected plants to flower and produce fully mature dry seed.

Will leeks cross with onions?

Leeks generally do not cross with common bulb onions, but different compatible leek varieties can cross with one another.

Is Seedmart Large American Flag leek seed chemically treated?

The current product is identified as having no chemical treatment. Check the product specifications before each order because seed lots can change.

Is Large American Flag open pollinated?

Yes. The current product is identified as an open-pollinated, non-hybrid heirloom.

How many Large American Flag leek seeds are in one gram?

The current product specification lists approximately 375 seeds per gram.

What quantities of leek seed are available?

The current Large American Flag product is available in 10 g, 100 g and 250 g quantities.

Can Large American Flag leek seed be shipped to Western Australia or Tasmania?

The current product page states that this seed is not shipped to Western Australia or Tasmania because of quarantine restrictions.

Large American Flag leek seeds for Australian growers

Grow Leeks in Packet or Larger Quantities

Seedmart supplies Large American Flag leek seed for household gardens, raised beds, deep containers, market gardens and commercial vegetable production. Grow this traditional Allium ampeloprasum heirloom for thick white stems, mild onion-like flavour and dependable cool-season harvests.

Review the product page for current pack sizes, seed treatment, specifications, quarantine restrictions and ordering information before purchasing.