Wild petunia
Ruellia humilis ·
Lavender, petunia-like trumpets open fresh each morning from June to September on a low, hairy plant. A native of dry prairies, and unrelated to true petunias.
- Size
- 16 in tall, 16 in wide
- Zones
- 4 to 8
- Light
- Full sun
- Flowers
- Mid June to early September
- Pets
- Not checked
- Job in a bed
- Edging
A bed built around wild petunia
The planner designed this bed around wild petunia when this page was made: a 12 × 6 ft (3.7 × 1.8 m) cottage garden in zone 6, full sun. It chose the other plants from the 715 that suit those conditions and its dry soil, and says below why wild petunia stands where it does.
The plants
- 1 Wild petunia × 3, lavender
- 2 Winter heath × 10, pink
- 3 Sea thrift × 5, white
- 4 Switchgrass 'Cheyenne Sky' × 8, purple
- 5 Clary sage × 3, lavender
- 6 Silver sage × 1, silver leaves
- 7 Ornamental onion 'Purple Sensation' × 4, purple
- 8 Pink lily leek × 12, pink
Why this plant
- The only trumpets. The others are bells, globes, airy sprays and others. Shape reads at a distance, where colours blur.
- The only medium leaves here. The rest are fine and bold. A change of leaf keeps plants distinct when nothing is in flower.
Why here
- In the middle. At 16 in it is seen over winter heath (10 in) in front of it.
- A step in the back row. Next to switchgrass 'Cheyenne Sky' (3 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 3 plants in one group. Massed, one kind reads as a single shape. Scattered, it would look spotty.
Why now
- In flower for 13 weeks. From mid June to early September.
- Part of the bed's peak. With sea thrift and pink lily leek in mid June: 3 kinds at once. No week has more.
Planned as a cottage garden: 30 of the 30 plants (100%), bulbs aside, stand alone or in groups of no more than five, small enough for the kinds to mingle. Lavender, pink, purple and white make a cool, restful scheme. The most in flower at one time is 3 kinds, from late May.
The planner's own design check: 14 Excellent, 3 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where wild petunia goes in a border
At 16 in it belongs at the front of a bed. In the planner's ten height classes it is short (12 to 18 in).
Its job: edging. A low, neat plant used in short runs of three or five along the front to finish the edge (or, in a formal bed, in one even row).
A long season of soft colour at the front of a dry planting. It comes up late in spring, and seeds itself modestly into gaps.
- The front of a dry, sunny bed
- Prairie and gravel gardens
- A native groundcover for poor soil
What to plant with wild petunia
Plants recorded as good partners for it, and what each pairing does:
- Butterfly weed: in flower together for seven weeks, from late June; happy in the same dry soil.
- Prairie dropseed: in flower together for four weeks, from mid August; tall enough (2½ ft) to stand behind it; happy in the same dry soil.
- Purple coneflower: in flower together for 11 weeks, from late June; tall enough (3 ft) to stand behind it.
Questions about wild petunia
Does wild petunia need sun or shade?
Wild petunia grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled.
What zones does wild petunia grow in?
USDA zones 4 to 8. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does wild petunia flower in my zone?
In zone 5 it flowers mid June to early September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Late June to early September |
|---|---|
| Zone 5 | Mid June to early September |
| Zone 6 | Mid June to early September |
| Zone 7 | Early June to early September |
| Zone 8 | Early June to early September |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should wild petunia be planted?
12 in (30 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 16 in (40 cm), so a group knits into one patch.
It grows 16 in (40 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many wild petunia plants do I need?
At 12 in apart, set out in staggered rows:
- 12 to fill 10 square feet (about 1 m²)
- 11 for a single row 10 ft (3 m) long
- 38 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as runs of three or five along the front (or one even row, in a formal bed).
In the bed above, the planner used three in one group.
Will wild petunia spread?
It seeds itself about; the risk of it taking over is moderate. Self-seeds freely. Remove the spent flowers to limit seedlings.
What flowers after wild petunia?
Wild petunia is over by early September. These start as it finishes and carry the same spot on, so it never goes flat:
- Garden chrysanthemum: from mid September to late October, 24 in tall.
- October daphne: from mid September to late October, 8 in tall, to stand in front of it and cover its fading stems.
- Meadow saffron: from mid September to mid October, 6 in tall, to stand in front of it and cover its fading stems.
What does wild petunia look like in winter?
Wild petunia dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
In these guides
Every fact on record
- Type
- Perennial
- Size
- 16 in (40 cm) tall, 16 in (40 cm) wide
- Plant
- 12 in (30 cm) apart
- Height class
- Short (12 to 18 in)
- Place in the bed
- Front
- Flowers
- Mid June to early September; trumpets; lavender
- Leaves
- Medium texture, herbaceous; green
- Shape
- Mounding, self-seeding
- Hardy in
- USDA zones 4 to 8
- Light
- Full sun
- Soil
- Lean, dry and sharply drained
- Water
- Low
- Feeding
- None needed
Not yet checked against an outside reference: its figures rest on general horticultural knowledge. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.