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perennial

Swamp milkweed

Asclepias incarnata

Climate-suitable non-native

Growing guidance

Horticultural figures below are practitioner estimates for planning, pending expert review. The botanical record further down is sourced and verifiable.

Current-climate suitability

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Future-climate resilience

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Sun

Full sun

Soil moisture

moisture-retentive, waterlogged

Heat tolerance

Up to about 38°C

Cold tolerance

Down to about -32°C

Waterlogging tolerance

5/5

Drought tolerance

2/5

Mature size

0.9–1.5 m tall, 0.6 m spread

Seasonal interest

Summer · Rose pink

Maintenance

low

Wildlife supported

General wildlife value 5/5 (verified species relationships are shown only where structured data exists)

How to plant it

General steps for this plant. Save a garden and these become specific to your location, soil and light.

  1. Step 1When to plant

    Plant during March to May or September to November.

    Autumn planting gives roots a head start; spring planting suits cold or wet soils.

  2. Step 2Where to put it

    Choose a position in full sun for most of the day. Allow 0.6 m of room around it — mature spread is 0.6 m and mature height 0.9–1.5 m.

    Light in your garden is not answered, so this is the plant's own requirement.

  3. Step 3Preparing the ground

    Dig a hole twice as wide as the root ball and no deeper, loosen the sides, and plant so the top of the root ball is level with the surrounding soil.

    Soil is not answered. This plant grows in moisture-retentive, waterlogged conditions.

  4. Step 4Watering while it establishes

    Water thoroughly at planting (5–10 litres), then only when the top few centimetres of soil are dry, through the first growing season.

    Even a drought-tolerant plant (2/5 here) only becomes drought-tolerant once established.

  5. Step 5Mulch

    Spread 5–7 cm of composted bark or garden compost around the plant, keeping it clear of the stem.

    Mulch cuts water loss and suppresses weeds through the first summer, when losses are most likely.

  6. Step 6The first year

    Check it after strong wind and in long dry spells. Little else is needed.

    Maintenance level on the plant record is low.

  7. Step 7What to watch for

    Sap is an irritant; wear gloves. Toxicity: notable. Site it accordingly if children or pets use the space.

    Taken from the plant record and your measured climate figures, not from a general description.

Spacing: about 0.6 m apart — roughly 28 plants for every 10 m² if planted as a group.

What this guide could not use

  • No location saved, so planting times are general rather than local.
  • Soil moisture is not answered, so soil preparation is general advice.
  • Light is not answered, so the position below is the plant's own preference.
  • Whether you can water is not answered, so watering assumes hand watering.
Answer five questions to make this specific

Built by fixed rules from: Plant record for Swamp milkweed (last reviewed 2026-06-01). Planting guide version gf-planting-1.0.0. Timings and volumes are practitioner estimates for planning, not a substitute for local nursery advice.

Known risks or warnings

Sap is an irritant; wear gloves.

Toxicity: notable

Status and jurisdiction

Climate-suitable non-native in United Kingdom (Great Britain).

Register consulted: GBIF Backbone Taxonomy distributions for Great Britain

Record review status: reviewed · last reviewed 2026-06-01 · plant data version gf-plants-2026.09.18. Status claims are never inferred from climate similarity, and growing figures are estimates pending expert review.

Verified botanical record

Accepted scientific name
Asclepias incarnata L.
Family
Apocynaceae (Gentianales)
Rank and status
species · accepted
GBIF record
Taxon 3170266

Recorded as introduced in: Belgium, Flemish Region, South European Russia

Ranges are exactly as recorded in the GBIF source checklists and may be incomplete for widely cultivated species.

Asclepias incarnata, the swamp milkweed, rose milkweed, rose milkflower, swamp silkweed, or white Indian hemp, is a herbaceous perennial plant species native to North America. It grows in damp through wet soils and also is cultivated as a garden plant for its flowers, which attract butterflies and other pollinators with nectar. Like most other milkweeds, it has latex containing toxic steroids, a characteristic that repels many species of insects and mammals.

Description from Wikipedia — Asclepias incarnata (CC BY-SA), shortened and unedited in substance.

Native status and geographic context

  • United Kingdom: climate-suitable
  • United States: native
  • Australia: climate-suitable

Native status is never inferred from climate similarity. Plants restricted or invasive in a jurisdiction are excluded from recommendations there.

What to do next

Create a Garden Profile to see whether this plant suits your conditions.

Demonstration data

These figures come from the demonstration dataset kept for testing and as a fallback when the measured climate service is unavailable. They are representative, not observed, and are never presented as validated live data.