GrowingHQ
OrnamentalclimberStraightforward

Passionflower

Passiflora caerulea

An extraordinary-looking flower on a plant that is far tougher than it appears — the blue passionflower is hardy in most of Britain against a wall, grows several metres in a season, and produces orange egg-shaped fruits in a good summer that are edible and not worth eating.

Position
Full sun or Partial shade
Water
moderate demand
Drainage
Free-draining
Grows to
400–900 cm × 200–400 cm
Hardiness
H4
Harvest
September and October
Difficulty
Straightforward

August

In flower

Coming next month: harvest.

Passionflower’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
PlantMay. June.
In flowerJune. July. August. September.
HarvestSeptember. October.
PruneMarch. April.

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, Partial shade
Frost
Hardy
Hardiness rating
H4 (RHS)
Grows best at
12–28 °C
Soil
Loam, Sandy, Chalky
Soil pH
6–7.5
Drainage
Free-draining
Water needs
moderate
Drought
moderate tolerance
Waterlogging
poor tolerance
Heat
good tolerance
Wind and exposure
poor tolerance
Where these figures come from
LightSourced guidancemoderate confidence
  • Royal Horticultural Society: Passionflower — position

Checked 2026-08-13

FrostSourced guidancehigh confidence
  • Royal Horticultural Society: Passionflower — 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: Passionflower — temperature

Checked 2026-08-13

SoilSourced guidancemoderate confidence
  • Royal Horticultural Society: Passionflower — soil

Checked 2026-08-13

Soil pHSourced guidancemoderate confidence
  • Plant Finder — Missouri Botanical Garden: Passiflora caerulea — culture

Checked 2026-08-13

DrainageSourced guidancemoderate confidence
  • Royal Horticultural Society: Passionflower — 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 conditionPassionflower 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 Passionflower as it stands: The pH suits it: it wants 6 to 7.5, 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.
Chalky and alkalineGrows well herePassionflower grows perfectly well on chalky and alkaline without special measures, though it is not the soil it would choose.
LoamPrefers this soilLoam suits Passionflower as it stands: The pH suits it: it wants 6 to 7.5, 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 Passionflower as it stands: The pH suits it: it wants 6 to 7.5, 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 conditionPassionflower 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 Passionflower as it stands: The free drainage is exactly what it wants. Loam is among the soils it is recorded as suiting.
Made ground and urban soilWorks, with one conditionPassionflower 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
400–900 cm
Mature spread
200–400 cm
Rooting depth
50 cm
Spacing
200–300 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: Passionflower — spacing

Checked 2026-08-13

How far apart to plant passionflowerThree passionflower plants drawn in a row at their recorded spacing of 200–300 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.200–300 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.

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
Semi-evergreen — holds its leaves in a mild winter
In a container
Workable in a container, with conditions
Where these figures come from
FoliageSourced guidancehigh confidence
  • Royal Horticultural Society: Passiflora caerulea — foliage

Checked 2026-08-13

In a containerHorticultural consensusmoderate confidence

No external citation — see the evidence type above.

Checked 2026-08-13

How it climbs
Tendrils or leaf stalks — needs mesh or wire to grip
Vigour
Vigorous — needs a substantial support and annual attention
Where these figures come from
How it climbsSourced guidancehigh confidence
  • Royal Horticultural Society: Passiflora caerulea — support

Checked 2026-08-13

VigourSourced guidancemoderate confidence
  • Royal Horticultural Society: Passiflora caerulea — vigour

Checked 2026-08-13

Support it needs. Wires, mesh or trellis for the coiling tendrils to grip. Train the main stems horizontally while they are young — flowering shoots break upwards along a horizontal stem, so a fan multiplies the display over a vertical one.

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

GreenhouseWell suited
source

Sourced guidancemoderate confidence

  • Agriculture and Horticulture Development Board — AHDB: Passiflora under protection

Checked 2026-08-13

Raised bedWorkable
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

ContainerWorkable
source

Sourced guidancemoderate confidence

  • Royal Horticultural Society: Growing method suitability

Checked 2026-08-13

PolytunnelWorkable
source

Sourced guidancemoderate confidence

  • Agriculture and Horticulture Development Board — AHDB: Passiflora under protection

Checked 2026-08-13

Growing it

  • TrainingIt climbs by coiling tendrils, so wires, mesh or trellis all work and a bare wall does not. Spread the main stems horizontally while young: flowers come from shoots that break along a horizontal stem, so training it sideways multiplies the display.
  • PruningWait until April before cutting winter damage out. Passiflora caerulea often looks dead after a hard winter and shoots strongly from the base or from apparently lifeless wood — cutting in February frequently removes stems that would have recovered.
Where this guidance comes from
TrainingSourced guidancemoderate confidence
  • Royal Horticultural Society: Passiflora — training

Checked 2026-08-13

PruningSourced guidancemoderate confidence
  • Royal Horticultural Society: Passiflora caerulea — pruning

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.

Is it worth putting under cover?

Whether it will grow there is on the methods table above. This is whether the space is well spent, which is a different question and usually the one being asked.

StructureWhat protection is worthWhat decides it
GreenhouseOnly possible under cover
source

GrowingHQ editorial positionmoderate confidence

What protection is worth for this crop, judged against the same standard as every other record in this file.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

Fruit ripening. The plant is hardy enough to survive outdoors in the south and the fruit almost never ripens there; under glass it does.Room for a permanent vine on wires; Hand pollination in a closed houseThe distinction people miss is that surviving and fruiting are different questions for this plant. Outdoors it answers yes and no.
PolytunnelExtends the season
source

GrowingHQ editorial positionmoderate confidence

What protection is worth for this crop, judged against the same standard as every other record in this file.

  • GrowingHQ editorial synthesis — GrowingHQ

Checked 2026-08-13

Overnight temperature. Glass holds overnight heat that polythene loses, so a tunnel runs cooler at night than a greenhouse in the same garden. For a crop at the edge of its heat requirement that difference decides whether the fruit ripens.

Safety and edibility

  • Which parts are ediblechildrenThe ripe orange fruit of Passiflora caerulea is edible and bland. Unripe green fruit contains cyanogenic compounds and causes stomach upset, and the leaves are not edible at all — this is not the same species as the commercial passion fruit, Passiflora edulis.
    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Passiflora caerulea — fruit

    Checked 2026-08-13

    Eat only fully ripe orange fruit, and tell children the green ones are not food. There is little reason to eat them at all beyond curiosity.

Sources for this page

Agriculture and Horticulture Development Board · 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.