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Ornamentalshrub ornamentalStraightforward

Buddleja

Buddleja davidii

The butterfly bush: superb for nectar, effectively unkillable, and listed as an invasive non-native in Britain, where it colonises railway embankments, walls and derelict ground from wind-blown seed. Growing it is a choice worth making deliberately, and deadheading before it seeds is the difference between a garden plant and a source.

Position
Full sun
Water
low demand
Drainage
Free-draining
Grows to
200–400 cm × 200–400 cm
Hardiness
H6
Flowers
July to September
Difficulty
Straightforward

August

In flower

Coming next month: plant.

Buddleja’s year

Resolved for United Kingdom (general). Every window is stored against a climate event rather than a date, so a late frost pocket runs later than the band shows. What else August calls for.

ActivityJFMAMJJASOND
PlantMarch. April. September. October.
In flowerJuly. August. September.
PruneMarch.

Timing that travels

The band above resolves this plant's windows into months for one region. These are the windows themselves, stored against a climate event rather than a date — which is the form that survives being carried to a colder garden, a frost pocket, or next year.

Conditions it needs

Light
Full sun
Frost
Very hardy
Hardiness rating
H6 (RHS)
Grows best at
15–28 °C
Soil
Sandy, Loam, Chalky, Clay
Soil pH
5.5–8
Drainage
Free-draining
Water needs
low
Drought
good tolerance
Waterlogging
moderate tolerance
Heat
good tolerance
Wind and exposure
good tolerance
Where these figures come from
LightSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja — position

Checked 2026-08-13

FrostSourced guidancehigh confidence
  • Royal Horticultural Society: Buddleja — hardiness

Checked 2026-08-13

Hardiness ratingSourced guidancemoderate confidence
  • Royal Horticultural Society: RHS hardiness ratings

Checked 2026-08-13

Grows best atSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja — temperature

Checked 2026-08-13

SoilSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja — soil

Checked 2026-08-13

Soil pHSourced guidancemoderate confidence
  • Plant Finder — Missouri Botanical Garden: Buddleja davidii — culture

Checked 2026-08-13

DrainageSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja — soil

Checked 2026-08-13

Water needsHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

DroughtHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

WaterloggingHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

HeatHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Wind and exposureHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

On your soil

Computed by comparing this plant's recorded requirements against each soil's recorded characteristics. A recorded horticultural fact overrides the comparison where GrowingHQ holds one.

SoilVerdictWhy
Heavy clayWorks, with one conditionBuddleja will crop on heavy clay, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
SandyPrefers this soilSandy suits Buddleja as it stands: The pH suits it: it wants 5.5 to 8, and this soil is in that range. The free drainage is exactly what it wants. Sandy soil is among the soils it is recorded as suiting. It stands dry conditions better than most, which this soil will test.
Chalky and alkalinePrefers this soilChalky and alkaline suits Buddleja as it stands: The free drainage is exactly what it wants. Chalky soil is among the soils it is recorded as suiting. It stands dry conditions better than most, which this soil will test.
LoamPrefers this soilLoam suits Buddleja as it stands: The pH suits it: it wants 5.5 to 8, and this soil is in that range. The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. The soil holds moisture, which saves a great deal of watering.
SiltyPrefers this soilSilty suits Buddleja as it stands: The pH suits it: it wants 5.5 to 8, and this soil is in that range. The free drainage is exactly what it wants. The soil holds moisture, which saves a great deal of watering.
Peaty and acidWorks, with one conditionBuddleja will crop on peaty and acid, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.
Shallow over rockPrefers this soilShallow over rock suits Buddleja as it stands: The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting. It stands dry conditions better than most, which this soil will test.
Made ground and urban soilWorks, with one conditionBuddleja will crop on made ground and urban soil, but one thing has to be dealt with first. It needs ground that drains, and this soil holds water. A plant that stays in the ground through winter with its roots in cold, saturated soil rots — which is what kills most of what fails on heavy ground, rather than the cold.Improve the drainage before planting — a raised bed, or bulky organic matter worked in over several seasons. Do not add sand to clay in small quantities; it makes the problem worse.

Not sure which you have? Four hand tests will settle it.

Space and spacing

Mature height
200–400 cm
Mature spread
200–400 cm
Rooting depth
60 cm
Spacing
150–300 cm apart
Where these figures come from
Mature heightHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Mature spreadHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Rooting depthHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

SpacingSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja — spacing

Checked 2026-08-13

How far apart to plant buddlejaThree buddleja plants drawn in a row at their recorded spacing of 150–300 cm between plants. The spacing is drawn to scale against a one metre rule; the plants themselves are symbols rather than scale drawings, so the distance between them is the part to read.150–300 cmone metre
Measured centre to centre. Plants set closer than this compete for light and water long before they look crowded, and the crowding cannot be undone once they are in.

In a container

Minimum volume
40 litres or more
Minimum depth
45 cm
Where the container figures come from
Minimum volumeHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Minimum depthHorticultural consensusmoderate confidence
  • Royal Horticultural Society: Buddleja davidii — cultivation

Checked 2026-08-13

Only the compact dwarf cultivars are realistic in a pot.

Habit and ultimate size

What the plant becomes, rather than what it is when you buy it. The gap between the two is where most planting mistakes live.

Foliage
Deciduous
In a container
Not a realistic container plant
Where these figures come from
FoliageSourced guidancehigh confidence
  • Royal Horticultural Society: Buddleja davidii — foliage

Checked 2026-08-13

In a containerHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Growth rate
Fast — over about 60 cm a year
Ultimate height
200–400 cm
Ultimate spread
200–400 cm
Time to reach it
5–10 yearsSourced guidance
Where these figures come from
Growth rateSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja davidii — growth rate

Checked 2026-08-13

Ultimate heightSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja davidii — ultimate height

Checked 2026-08-13

Ultimate spreadSourced guidancemoderate confidence
  • Royal Horticultural Society: Buddleja davidii — ultimate spread

Checked 2026-08-13

Time to reach itSourced guidancelow confidence
  • Royal Horticultural Society: Buddleja davidii — time to ultimate size

Checked 2026-08-13

Cutting it back. Cut hard back to a low framework every spring. It flowers on the current season's growth, so this costs nothing and is the only thing that keeps it from becoming a leggy four-metre thicket flowering out of sight.
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

How it spreads. Seeds itself enthusiastically into walls, gutters and waste ground, and is a recognised problem plant on masonry rather than in gardens. Deadheading before the seed ripens is a good-neighbour act rather than a horticultural one.
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Where and how you can grow it

Each way of growing is assessed separately, and “not assessed” is a real answer rather than a gap we have filled in with a guess.

MethodSuitabilityWhat it needs
Open groundWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Traditional dug bedWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Raised bedWell suited
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

ContainerMarginal
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Dwarf cultivars only
HydroponicsNot suitable
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

Growing it

  • PruningCut back hard to about 60 cm every March. Buddleja flowers on new wood, so hard pruning produces more and larger flower spikes; left unpruned it becomes a tall bare-legged shrub flowering out of reach.
  • ProtectionDeadhead the spent flower spikes before they set seed. A single plant produces very large quantities of wind-borne seed, and this one step is what separates growing it responsibly from adding to a recognised problem.
Where this guidance comes from
PruningSourced guidancehigh confidence
  • Royal Horticultural Society: Buddleja — pruning

Checked 2026-08-13

ProtectionSourced guidancehigh confidence
  • Royal Horticultural Society: Buddleja — invasiveness

Checked 2026-08-13

Where to make a pruning cutFour stems compared. The first is cut cleanly on a slope about five millimetres above an outward-facing bud, sloping away from it, and is labelled correct. The second is cut too far above the bud, leaving a long stub that dies back. The third is cut too close, into the bud itself, which loses the shoot. The fourth is cut sloping towards the bud so rain runs onto it rather than away, which rots it. In every case the bud points outwards, away from the centre of the plant.Correct5 mm, sloping awayToo highstub dies backToo closebud lostSloping inrain sits on the bud
The bud you cut to becomes the new shoot, and it grows in the direction it points — which is why an outward-facing bud opens the plant up and an inward-facing one crosses the middle.

What goes wrong

ProblemHow oftenNotes
Capsid bugoccasional
source

Horticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

Safety and edibility

  • Legal requirementBuddleja davidii is recognised in Britain as an invasive non-native species. It is NOT listed under Schedule 9 of the Wildlife and Countryside Act, so planting it in a garden is not an offence and it remains freely on sale — a distinction worth stating, because it is often described as though it were banned. What does apply is the general position on invasive plant waste: material capable of spreading is controlled waste, and allowing an invasive plant to spread onto neighbouring or open land can create a liability.
    source

    Legal or label requirementhigh confidence

    • GOV.UK guidance — UK Government: Invasive non-native plants — prevent the spread

    Checked 2026-08-13

    Deadhead before the seed sets, which is the single effective control. Dispose of seed heads and prunings through your council's garden waste service or by burning where permitted, rather than fly-tipping or open composting near walls, railway land or waste ground. Sterile and low-seeding cultivars are widely available and are the better choice near open land.

Sources for this page

GOV.UK guidance · GrowingHQ editorial synthesis · Plant Finder · Royal Horticultural Society

Each figure on this page carries its own citation, under the “where these figures come from” note in its section. Record last reviewed 2026-08-14.