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Rose 'Double Knock Out'

Rosa 'Radtko' (Double Knock Out) · Rosaceae Popular

Rose 'Double Knock Out' (Rosa 'Radtko' (Double Knock Out)) in flower
Photo: Photo by David J. Stang, via Wikimedia Commons (CC BY-SA 4.0)

Fully double, cherry-red flowers, like a small florist's rose, in flush after flush from spring to hard frost.

Size
4 ft tall, 4 ft wide
Zones
5 to 9
Light
Full sun
Flowers
Late May to mid October
Pets
No toxicity recorded
Job in a bed
Anchor

A bed built around rose 'Double Knock Out'

The planner designed this bed around rose 'Double Knock Out' when this page was made: a 16 × 8 ft (4.9 × 2.4 m) English border in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why rose 'Double Knock Out' stands where it does.

A 16 × 8 ft (4.9 × 2.4 m) bed at eye level in early August: Rose 'Double Knock Out', Creeping phlox 'Candy Stripe', Sea thrift, White mugwort, Wild quinine, Anise hyssop, Ornamental onion 'Purple Sensation', Asiatic lily, Persian fritillary.
A 16 × 8 ft (4.9 × 2.4 m) English border in zone 6, full sun, seen from the path in early August.
4. White mugwort44. White mugwort44. White mugwort41. Rose 'Double Knock Out'12. Creeping phlox 'Candy Stripe'22. Creeping phlox 'Candy Stripe'22. Creeping phlox 'Candy Stripe'23. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift32. Creeping phlox 'Candy Stripe'22. Creeping phlox 'Candy Stripe'22. Creeping phlox 'Candy Stripe'22. Creeping phlox 'Candy Stripe'22. Creeping phlox 'Candy Stripe'25. Wild quinine55. Wild quinine55. Wild quinine55. Wild quinine55. Wild quinine54. White mugwort48. Asiatic lily88. Asiatic lily88. Asiatic lily89. Persian fritillary99. Persian fritillary99. Persian fritillary97. Ornamental onion 'Purple Sensation'77. Ornamental onion 'Purple Sensation'77. Ornamental onion 'Purple Sensation'73. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift33. Sea thrift36. Anise hyssop66. Anise hyssop66. Anise hyssop66. Anise hyssop66. Anise hyssop67. Ornamental onion 'Purple Sensation'77. Ornamental onion 'Purple Sensation'78. Asiatic lily89. Persian fritillary98. Asiatic lily8
From above, to scale. Each circle is one plant, as wide as the room it needs.

The plants

  1. 1 Rose 'Double Knock Out' × 1, red
  2. 2 Creeping phlox 'Candy Stripe' × 8, pink
  3. 3 Sea thrift × 13, white
  4. 4 White mugwort × 4, cream
  5. 5 Wild quinine × 5, white
  6. 6 Anise hyssop × 5, lavender
  7. 7 Ornamental onion 'Purple Sensation' × 5, purple
  8. 8 Asiatic lily × 5, orange
  9. 9 Persian fritillary × 4, purple

Why this plant

  • The bed's only structure. Shrubs and grasses keep their shape when the perennials die down, and it is the only one here.
  • The only red.

Why here

  • Anchors a back corner. At 4 ft it is one of the taller plants here, and the tallest close the ends of the bed, where they stand in front of nothing.
  • A step in the back row. Next to ornamental onion 'Purple Sensation' (2½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
  • One plant, alone. A shrub is seen as an object, and needs clear ground around it.

Why now

  • In flower for 21 weeks. From late May to mid October.
  • Closes the season. For its last four weeks nothing else on the plan is in flower.

Planned as an English border: 8 of the 8 groups (100%) are drifts, longer along the bed than they are deep. Creeping phlox 'Candy Stripe' is the first into flower, in mid April, and rose 'Double Knock Out' the last to finish, in mid October. The bed is balanced: the left half carries 49% of the visual weight and the right half 51%. Every line of the Design check comes out Good or better.

The planner's own design check: 8 Excellent, 9 Good.

Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.

Where rose 'Double Knock Out' goes in a border

At 4 ft it belongs at the back of a bed. In the planner's ten height classes it is moderately tall (3 to 4 ft).

Its job: anchor. A shrub that gives the bed permanent structure. Planted singly, as soon as the front edge is laid; everything else is arranged around it.

The double form of the best-selling rose in North America. Like the original it shrugs off black spot and needs no deadheading. Cut it back hard in early spring.

  • Low-care colour all season
  • Hedges and massing
  • Foundation planting in sun

What to plant with rose 'Double Knock Out'

Plants recorded as good partners for it, and what each pairing does:

Questions about rose 'Double Knock Out'

Does rose 'Double Knock Out' need sun or shade?

Rose 'Double Knock Out' grows in full sun (6 or more hours of direct sun a day).

It wants ordinary well-drained soil, of average fertility, and a good soak in dry spells.

What zones does rose 'Double Knock Out' grow in?

USDA zones 5 to 9. It is hardy to zone 5, which means it survives winter nights down to about −10 °F (−23 °C).

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does rose 'Double Knock Out' flower in my zone?

In zone 5 it flowers late May to mid October. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.

Roughly when rose 'Double Knock Out' is in flower
Zone 5Late May to mid October
Zone 6Late May to mid October
Zone 7Mid May to mid October
Zone 8Early May to mid October
Zone 9Early May to mid October

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 rose 'Double Knock Out' be planted?

3½ ft (100 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 4 ft (120 cm), so a group knits into one patch.

It grows 4 ft (120 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many rose 'Double Knock Out' plants do I need?

At 3½ ft apart, set out in staggered rows:

  • 1 to fill 10 square feet (about 1 m²)
  • 4 for a single row 10 ft (3 m) long
  • 3 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one, planted singly: it is the bed's structure, and everything else is arranged around it.

In the bed above, the planner used one in one group.

Is rose 'Double Knock Out' poisonous to dogs and cats?

No toxicity is recorded for dogs, cats, horses or people, according to the ASPCA.

"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.

What flowers after rose 'Double Knock Out'?

Rose 'Double Knock Out' is over by mid October. These start as it finishes and carry the same spot on, so it never goes flat:

What does rose 'Double Knock Out' look like in winter?

Rose 'Double Knock Out' drops its leaves and stands as bare branches. That is when to see its shape, and to prune it if it needs pruning.

More Rosa

In these guides

Zone guides: Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9

In flower in: May · June · July · August · September · October

Every fact on record

Type
Shrub
Size
4 ft (120 cm) tall, 4 ft (120 cm) wide
Plant
3½ ft (100 cm) apart
Height class
Moderately tall (3 to 4 ft)
Place in the bed
Back
Flowers
Late May to mid October; open bowls; red
Leaves
Medium texture, deciduous; dark green
Shape
Rounded, clumping
Hardy in
USDA zones 5 to 9
Light
Full sun
Soil
Average, well-drained
Water
Moderate
Feeding
Light, in spring
Family
Rosaceae

Checked against ASPCA poison lists. 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.