Lagarosiphon major

RHS Plant Profile
curly waterweed

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curly waterweed visionspictures.com

Other common names

curly water thyme, giant water thyme

Synonyms

Elodea crispa

Aquatic

This plant is listed as an invasive non-native species in the UK – see Cultivation section for details. A submerged perennial with dense, recurved, dark green leaves. It produces small, inconspicuous, white to pale‑pink flowers in summer

Position

Full sun

Soil Types

Loam

Max Height

Up to 10 cm

Max Spread

0.5-1 metres

Size

Time to Maturity
5–10 years
Max Spread
0.5-1 metres
Max Height
Up to 10 cm

Growing Conditions

Loam
Moisture
Poorly–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
South–facing or East–facing or West–facing
Exposure
Exposed or 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)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Hydrocharitaceae
Native to GB/Ireland
No
Foliage
Semi evergreen
Habit
Submerged
Genus
Lagarosiphon are semi-evergreen, submerged aquatic perennials forming a cluster of branched stems clothed in spirally arranged, linear-lanceolate leaves, and tiny white or pink flowers in summer
Name Status
Correct

How to Grow

Cultivation

This plant is listed on Schedule 9 of the Wildlife & Countryside Act (1981), the GB Non-Native Species Secretariat list of Species of Special Concern and the EU list of Invasive Alien Species of Union Concern (applies in NI). It should not be planted or caused to grow in the wild in the UK. It is also banned from sale, and gardeners who already have it should take steps to control it. See RHS advice on invasive non-native species for further information

Propagation

See cultivation notes

Pests

See cultivation notes

Diseases

See cultivation notes