• 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

Asclepias incarnata

swamp milkweed

  • Other common names swamp milkweed
    water nerveroot

  • Family Apocynaceae

  • Genus Asclepias can be evergreen or deciduous perennials or subshrubs, with simple, entire leaves and umbel-like clusters of small, distinctively shaped flowers followed by paired fruits containing seeds embedded in silky fibres

  • Details A.. incarnata is a thick-stemmed perennial with dense stems and narrow, mid-green leaves up to 15cm long. Clusters of dark purplish-pink flowers are produced from the upper part of the stems from mid-summer to early autumn, followed by narrow, upright seed pods up to 7cm long, green at first then turning pale brown before splitting to release the seeds with their parachutes

  • Plant range NE & SE USA


  • Foliage Deciduous

  • Habit Bushy

  • Toxicity All parts, particularly the roots, may cause mild stomach upset if ingested. Wear gloves and wash hands after handling

  • 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)




  • Full Sun

  • Aspect South-facing or West-facing

  • Exposure Sheltered


  • Clay


  • Loam


  • Sand


  • MoistureMoist but well-drained, Poorly-drained

  • SoilClay, Loam, Sand

  • pHAcid, Alkaline, Neutral


  • Ultimate height 1-1.5 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Grow outdoors in moist, fertile, loamy soil in full sun. Will thrive near a pond or stream

Propagation Propagate by seed or by division, or root basal cuttings in spring

Suggested planting locations and garden types Cottage & Informal Garden Prairie Planting

How to care

Pruning No pruning required

Pests Generally pest free

Diseases Generally disease free

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