Oslo F1 Certified Organic

SKU: LK452
A new organic variety for fall harvest. Oslo matures late fall to winter and can be left in the field or garden until early spring in areas with mild winters. Read More

Exposure Full Sun

Matures in 110 days

Season Cool Season

Seed type Hybrid, Organic ?

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New for 2025
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Oslo F1 Certified Organic

Product Details

A new organic variety for fall harvest. Oslo matures late fall to winter and can be left in the field or garden until early spring in areas with mild winters. White shanks are heavy and broad, topped with blue-green leaves. Easy to clean, which can be an issue with some late season varieties. Excellent hybrid uniformity that commercial growers will appreciate with the ability to hold well in storage.

Quick Facts:

    • Late season leek for fall and winter harvest.
    • Excellent choice for commercial growers.
    • Can be overwintered in regions with mild winter temperatures.
    • Stores well.

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All About Oslo F1 Certified Organic

Latin

Latin
Allium ampeloprasum var. porrum
Family: Amaryllidaceae

Difficulty

Difficulty
Easy, but slow. Transplanting is required.

Season & Zone

Season & Zone
Season:Β Cool season
Exposure: Full-sun
Zone:Β Winter harvestΒ leeks are hardy to Zone 7.

Timing

Timing
Start summer/fall harvest leeks 6-8 weeks before the last frost date, in flats indoors. Start winter harvest leeks indoors from March to mid-June. In mild winter areas, start them in a humus-rich nursery bed outside, and then transplant. Optimal soil temperature: 10-25Β°C (50-75Β°F). Seeds should sprout in 10-16 days.

Starting

Starting
In flats: Sow seeds 5mm (¼”) deep, about 1cm (½”) apart. Transplant when 20cm (8β€³) tall. Space 20cm (8β€³) apart in rows 45cm (18β€³) apart. Rows can be as narrow as 20cm (8") if planting in raised beds or other situation where weeding will be simple.

Growing

Growing
Ideal pH: 5.-6.5. Leeks have short roots, so the benefit from fertile soil with lots of compost and Β½ cupΒ balanced organic fertilizer worked in beneath each 2m (6β€²) of row. Traditional garden wisdom recommends using a dibber to make holes 15cm (6β€³) deep. Transplants are then set at the bottom of the hole and the hole is left unfilled – rain will fill it in as the leek grows. To blanch further up the stem, hill soil up around the stem as the leek grows, or mulch with straw.

However, the wise and much loved garden writer Linda Gilkeson asserts that there is no need to plant leeks into holes or trenches. She recommends transplanting the seedlings only at the depth of the soil plug they grow in. They will still produce nice, tall, blanched shanks, with no soil grains between the leaves.

In late fall, mulch around leeks as high up the stems as possible. If the forecast is for weather below -10Β° (14Β°Γβ€š cover them with a blanket or tarp.

Days to maturity:Β From transplant date.

Harvest

Harvest
Dig at any size, as needed. If winter harvest leeks freeze solid, wait until they thaw out during a warm spell to harvest.

Seed Info

Seed Info
In optimal conditions at least 65% of seeds will germinate. Usual seed life: 1 year. Per 100β€² row: 240 seeds, per acre: 70M seeds.

Companion Planting

Companion Planting
Grow leeks with beets, carrot, celery, onions, and spinach. Avoid planting near beans and peas. Leeks help repel carrot rust flies.

More onΒ Companion Planting.

How to Grow Leeks

Step 1

Timing

Start summer/fall harvest leeks 6-8 weeks before the last frost date, in flats indoors. Start winter harvest leeks indoors from March to mid-June. In mild winter areas, start them in a humus-rich nursery bed outside, and then transplant. Optimal soil temperature: 10-25Β°C (50-75Β°F). Seeds should sprout in 10-16 days.

Step 2

Starting

In flats: Sow seeds 5mm (¼”) deep, about 1cm (½”) apart. Transplant when 20cm (8β€³) tall. Space 20cm (8β€³) apart in rows 45cm (18β€³) apart. Rows can be as narrow as 20cm (8") if planting in raised beds or other situation where weeding will be simple.

Step 3

Growing

Ideal pH: 5.-6.5.

Leeks have short roots, so the benefit from fertile soil with lots of compost and Β½ cupΒ balanced organic fertilizer worked in beneath each 2m (6β€²) of row. Traditional garden wisdom recommends using a dibber to make holes 15cm (6β€³) deep. Transplants are then set at the bottom of the hole and the hole is left unfilled – rain will fill it in as the leek grows. To blanch further up the stem, hill soil up around the stem as the leek grows, or mulch with straw.

However, the wise and much loved garden writer Linda Gilkeson asserts that there is no need to plant leeks into holes or trenches. She recommends transplanting the seedlings only at the depth of the soil plug they grow in. They will still produce nice, tall, blanched shanks, with no soil grains between the leaves.

In late fall, mulch around leeks as high up the stems as possible. If the forecast is for weather below -10Β°β€š cover them with a blanket or tarp.

Step 4

Germination

Days to maturity: From transplant date.

In optimal conditions at least 65% of seeds will germinate. Usual seed life: 1 year. Per 100β€² row: 240 seeds, per acre: 70M seeds.

Step 5

Harvest

Dig at any size, as needed. If winter harvest leeks freeze solid, wait until they thaw out during a warm spell to harvest.

Tips

Companion Planting

Grow leeks with beets, carrot, celery, onions, and spinach. Avoid planting near beans and peas. Leeks help repel carrot rust flies.

Customer Reviews & Questions