Shrub · Rosaceae
Knock Out Rose
Rosa
Give it full sun and a yearly cleanup prune, and the Knock Out blooms from June to frost with almost no fuss.
Full sun
Every 7–14 days
USDA 5–9
3–4 ft · 0.9–1.2 m
Overview
The Knock Out rose changed what gardeners expect from a shrub rose. Breeder William Radler set out to make a rose that bloomed all season without the constant spraying and fussing older roses demand, and the original 'Radrazz' arrived in 1999. It belongs to the rose family and grows as a tough, low-care landscape shrub rather than a prized show rose.
What sets it apart is how little it asks. The shrub is self-cleaning, dropping its spent flowers on its own, and it reblooms from June right through to frost without deadheading. It stands up to black spot and powdery mildew, the fungal troubles that drove many gardeners away from roses, and once its roots take hold it shrugs off dry spells.
Size stays manageable too, holding to a rounded mound of 3 to 4 feet (91 to 122 cm) in most gardens. That makes it an easy fit for a foundation bed, a low hedge, or a large container, and the long bloom season earns its keep through summer and fall.
Care
The short version: full sun, well-drained loam, and a deep drink while it settles in, then water only in dry stretches once established. Mulch the root zone, feed in spring, and cut back about a third of the oldest canes each spring to keep it open and blooming.
Light
Knock Out roses bloom hardest in full sun, six to eight hours a day. They will take partial shade and keep going, but less light means fewer flowers and a looser, leggier shrub.
Water
Water deeply and often right after planting until the roots take hold, then ease off, since this rose is drought tolerant once established. A soak every 7 to 14 days in a dry spell is plenty, and about 3 inches of mulch held back from the stem keeps the soil from drying out.
Soil
Plant in well-drained loam with a pH between 6.0 and 7.0. The shrub is not fussy about soil, but good drainage matters most, so loosen heavy clay with compost before planting.
Temperature
This is a cold-hardy rose, taking winter lows near -20°F (-29°C) and summer heat up to 100°F (38°C). That range covers most temperate gardens with no special protection.
Humidity
Ordinary outdoor humidity suits it fine, so there is no number to hit. Good airflow counts for more, since crowded, still air is what lets the occasional fungal spot get started.
Feeding
Feed once in spring with a balanced rose or general-purpose fertilizer to fuel the first flush of growth. A seasonal feeding through the year keeps the blooms coming, and this undemanding shrub needs no more than that.
Pruning
Pruning needs are low. In spring, use the renewal method and cut about one-third of the oldest canes right down to the soil line to keep the shrub open and push fresh growth. Deadheading is optional, since the plant cleans itself, though snipping spent blooms can speed the next flush.
Repotting
In a container this rose rarely needs moving, but watch for roots circling or pushing out the drainage holes, water running straight through, or growth that stalls. Any of those means it is time to step up to a larger pot.
Size & spacing
The shrub settles into a rounded form of 3 to 4 feet (91 to 122 cm) tall and about as wide. Give each plant that same 3 to 4 feet (91 to 122 cm) of room so air moves freely and the canes never crowd.
When to plant
This is a cold-hardy shrub that survives winters down to -20°F (-29°C), so it lives in the garden year-round in zones 5 through 9. Plant it in spring once the last frost has passed, then enjoy a repeat show of bloom from June until frost shuts the season down.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring after last frost
- Harvest: June to frost (repeat blooming spring through fall)
Hardiness
USDA hardiness zones: 5–9
Temperature: down to -29°C
Troubleshooting
Knock Out roses dodge most of the trouble that plagues other roses, so problems are few. The big exception is rose rosette disease, which is fatal and worth learning to spot early. Match what you see below before you act.
Red, broom-like growth with a mass of soft thorns
This is rose rosette disease, a virus carried by a mite too small to see, and it is the one problem that can kill a Knock Out. The new canes turn bright red and bunch up like a witch's broom, covered in soft, pliable thorns. There is no cure, so dig the whole plant out, roots and all, bag it, and bin it before the mite moves on to its neighbors.
Fix:
- There is no cure; infected plants cannot be saved and the virus is systemic so it cannot be pruned out
- Promptly remove and bag the entire infected plant including roots and dispose of it
- Do not replant a rose in the same spot until remaining roots are gone
Leaves chewed to lace and ragged flowers in midsummer
Japanese beetles are the usual culprits, stripping the soft tissue between the veins until the leaves look like lace and gnawing the open blooms. Pick the beetles off into a jar of soapy water in the cool of the morning when they move slowly. This shrub is tough enough to shrug off light feeding, so step in only when aphids, thrips, or mites pile onto the tender new growth as well.
Fix:
- Hand-pick Japanese beetles into soapy water
- Tolerate minor feeding on this vigorous shrub
- Manage aphids with a strong spray of water or appropriate controls as needed
Black spots on the leaves that yellow and fall
This is black spot, a fungus that flares in warm, wet spells, but the Knock Out series was bred to resist it and a bad case is rare. The marks show up as round black blotches with feathery edges on the upper side of the leaf, and the leaf yellows and drops soon after. Rake up and bin the fallen leaves, open the plant to better airflow, and water at the base so the foliage stays dry.
Fix:
- Remove and dispose of fallen infected leaves
- Improve air circulation and avoid wetting foliage when watering
Toxicity
Good news for pet owners and parents: true roses are safe. Every part of this rose is non-toxic to cats, dogs, horses, and people, and the petals and hips are even edible. The only real hazard is the thorns, which can scratch a curious nose or prick a bare hand at pruning time.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe to be around. The only real risk is the thorns, which can scratch a curious nose or paw, and a cat that swallows a lot of woody stem could get an upset stomach.
Dogs None
No poisoning concern with this rose. Watch out for the thorns instead, since a dog that chews the canes can prick its mouth, and a big mouthful of stem is hard to digest.
Horses None
Listed as non-toxic by the ASPCA, so grazing the leaves or petals does no harm. The sharp thorns are the one thing to keep in mind.
Rabbits None
The leaves and petals are safe for rabbits to nibble. A thorn can still scratch, so a thornless stretch of stem is the kinder browse.
Livestock None
Cattle, goats, and sheep can browse the foliage without poisoning. The thorns are the only catch, and most animals simply graze around them.
Birds None
Nothing here will poison a bird, and many enjoy the cover the thorny canes give. The hips that follow the flowers are a welcome winter food.
People None
Roses are safe around people, and both the petals and the hips are edible. The thorns are the only hazard, so wear gloves when you prune.
Although non-toxic, the canes bear thorns that can cause mechanical injury (mouth or paw trauma); ingesting large amounts of stem material could pose a foreign-body obstruction risk.
Varieties
Knock Out is not one rose but a small family, with selections that vary the flower color, the petal count, and the size of the shrub. These are the ones you will run into most.
Knock Out (Rosa 'Radrazz')
The original 1999 to 2000 introduction from breeder William Radler, with single cherry-red blooms, and the cultivar the whole series grew out of.
Double Knock Out
A double-flowered form within the group that carries fuller, many-petaled blooms.
Pink Knock Out
The pink-flowered selection in the series for gardeners who want a softer color than the original red.
Rainbow Knock Out
A smaller selection that opens coral-pink blooms with a yellow eye at the center.
Petite Knock Out
The compact, miniature-scale form bred for small beds, edges, and containers.
How to propagate
Cuttings root readily enough, but there is a legal wrinkle worth knowing before you start a new plant from one you already own.
Stem cuttingsModerate
Late spring to summer from softwood or semi-hardwood growth · Several weeks to root, established over a season
Take cuttings from softwood or semi-hardwood growth in late spring through summer, and expect them to root over several weeks and settle in across a full season. One catch outweighs the technique here. This cultivar is patented under US Plant Patent PP#11836, so propagating it to sell or give away is legally restricted while the patent stands.
Myths
Knock Out roses are immune to every disease and never get sick.
They earn their name against black spot and powdery mildew, shrugging off the fungal troubles that plague older roses. But immune they are not. Rose rosette disease, a fatal virus with no cure, hits them just like any other rose, so watch for the red broom-like growth that gives it away.
Knock Out roses have to be deadheaded to keep flowering.
They are self-cleaning and drop their spent blooms on their own, then rebloom from spring to frost with no help from you. Snipping off the old flowers only speeds the next flush along, so it is a choice, not a chore.