• AGM plants

    AGM plants have been through a rigorous trial and assessment programme. They are:

    • Excellent for ordinary use in appropriate conditions
    • Available to buy
    • Of good constitution
    • Essentially stable in form & colour
    • Reasonably resistant to pests & diseases

Lobelia laxiflora

Sierra Madre lobelia

Sierra Madre lobelia

© RHS 1999

  • Other common names Sierra Madre lobelia

  • Family Campanulaceae

  • Genus Lobelia can be annuals, perennials or shrubs, with simple leaves and showy 2-lipped flowers that may be solitary or in racemes or panicles

  • Details L. laxiflora is an herbaceous, woody-based, rhizomatous perennial to 90cm tall, with arching stems bearing long, very narrow leaves and 4cm long tubular red and yellow flowers singly in the upper leaf axils in late spring and summer

  • Plant range SW USA to Colombia

Characteristics

  • Foliage Deciduous

  • Habit Bushy

  • Toxicity Ingestion may cause severe discomfort

  • 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)

    H3

Colour

Sunlight

  • Full Sun

  • Partial Shade

  • Aspect South-facing or West-facing

  • Exposure Sheltered

Soil

  • Sand

    Sand

  • Loam

    Loam

  • MoistureWell-drained, Moist but well-drained

  • SoilSand, Loam

  • pHAlkaline, Neutral

Size

  • Ultimate height 0.5-1 metres

  • Ultimate spread 1-1.5 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Of borderline hardiness - protect with a dry winter mulch or lift and store in a frost-free greenhouse. Prefers to be grown in deep, fertile, reliably moist soil in full sun or partial shade

Propagation Propagate by semi-ripe cuttings

Suggested planting locations and garden types Flower borders and beds City & Courtyard Gardens Coastal Cottage & Informal Garden

How to care

Pruning No pruning necessary, tidy up after flowering

Pests Slugs may be a problem

Diseases Crowns may rot in damp, mild conditions

Advertise here

Did you find the information you were looking for?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.