Lactuca sativa 'Oakus'

RHS Plant Profile
lettuce 'Oakus'

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A strong, leafy, biennial, butterhead variety of lettuce with striking, dark purple to almost black leaves, usually grown as an annual, with a good flavour and resistance to downy mildew. Sow from March to August for harvesting from June through to October

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

0.1-0.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
1 year
Max Spread
0.1-0.5 metres
Max Height
0.1-0.5 metres

Growing Conditions

Chalk Clay Loam Sand
Moisture
Moist but well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
South–facing or West–facing
Exposure
Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H2

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming
Genus
Lactuca can be annuals, biennials, perennials or shrubs, with alternate leaves, milky white sap and daisy-like flowers in white, yellow or blue. The genus includes a wide range of wild plants, as well as species cultivated for their edible leaves (lettuce)
Name Status
Accepted

How to Grow

Cultivation

Grow in full sun on moisture-retentive soil. Sow a short row every fortnight to ensure continuity of cropping. Use cloches or biodegradable horticultural fleece to protect early and late crops. See lettuce cultivation for more information and lettuce, butterhead and leafy trial 2025

Propagation

Propagate by seed. See sowing vegetable seeds

Suggested planting locations and garden types

  • City and courtyard gardens
  • Cottage and informal garden
  • Patio and container plants
  • Flower borders and beds
  • Wall side borders

Pruning

No pruning required

Pests

May be susceptible to grey moulds and downy mildews

Diseases

May be susceptible to grey moulds and downy mildews but this variety does show some resistance to mildew