Vernonia arkansana 'Mammuth'

RHS Plant Profile

Arkansas ironweed 'Mammuth'

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Other common names

great ironweed 'Mammuth'

Synonyms

Vernonia crinita 'Mammuth'

Herbaceous Perennial

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A clump-forming perennial to 1.8m tall with stout, upright, self-supporting stems densely clothed with narrow, lance-shaped leaves and dense clusters of rosy pink-mauve flowers from late summer to autumn

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam, Sand

Max Height

1.5-2.5 metres

Max Spread

0.5-1 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.5-1 metres
Max Height: 1.5-2.5 metres

Growing Conditions

Chalk Clay Loam Sand

Moisture: Moist but well–drained
pH: Acid or Alkaline or Neutral

Position

Full sun Partial shade

Aspect: East–facing or South–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): H7

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, Columnar upright
Genus: Vernonia are annuals, perennials, climbers, sub-shrubs, shrubs and trees, though only the perennials are in cultivation. They have upright stems, simple, stalkless leaves and flat branched heads of tubular purple or reddish pink, occasionally white, flowers
Name Status: Accepted

How to Grow

Cultivation

Cut back the old stems before onset of new growth in spring. Deadhead if self-seeding is a problem It will tolerate most soil types, but prefers rich, evenly moist soils in full sun or light shade. Mulch soils prone to drying out in summer

Propagation

Propagate by division in spring

Suggested planting locations and garden types

Cottage and informal garden
Prairie planting
Flower borders and beds

Pruning

Cut back the old stems before onset of new growth in spring. Deadhead if self-seeding is a problem

Pests

Generally pest-free

Diseases

Generally disease-free