Shrub · Rosaceae
Knock Out Rose
Rosa
Give it full sun and one easy cleanup prune a year, and your Knock Out rewards you with bloom from June to frost.
Full sun
Every 7–14 days
USDA 5–9
3–4 ft · 0.9–1.2 m
Overview
The Knock Out rose is a wonderful place to begin if roses have ever felt out of reach. Breeder William Radler wanted a rose that flowered all season long without the endless spraying and fussing that older roses seem to demand, and his original 'Radrazz' arrived in 1999. It sits in the rose family and grows as a forgiving, low-care landscape shrub rather than a delicate show rose, so mistakes here are easy to recover from.
The best part is how little it asks of you. The shrub is self-cleaning, letting go of its faded flowers on its own, and it reblooms from June clear through to frost with no deadheading required. It stands up to black spot and powdery mildew, the fungal headaches that scared many people off roses, and once its roots settle in it takes dry spells in stride.
It stays a comfortable size, too, keeping to a rounded mound of 3 to 4 feet (91 to 122 cm) in most gardens. That makes it a friendly fit for a foundation bed, a low hedge, or a roomy container, and you get a long, generous bloom season to enjoy through summer and fall.
Care
The short version: give it full sun, well-drained loam, and a good deep drink while it settles in, then water only during dry stretches once it is 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
Your Knock Out will bloom its heart out in full sun, six to eight hours a day. It will carry on in partial shade if that is what you have, though you can expect fewer flowers and a looser, leggier shape.
Water
Water deeply and often right after planting until the roots take hold, then you can ease right off, because this rose is drought tolerant once established. A good soak every 7 to 14 days during a dry spell is all it wants, and about 3 inches of mulch kept back from the stem helps the soil hold its moisture.
Soil
Plant it in well-drained loam with a pH somewhere between 6.0 and 7.0. It is not picky about soil, but drainage matters most, so work some compost into heavy clay before you plant and it will thank you.
Temperature
This is a tough, cold-hardy rose that takes winter lows near -20°F (-29°C) and summer heat up to 100°F (38°C). That wide range covers most temperate gardens with no special coddling needed.
Humidity
Everyday outdoor humidity suits it just fine, so there is no target number to chase. Good airflow matters far more, since it is crowded, still air that gives the odd fungal spot a chance to start.
Feeding
Feed it once in spring with a balanced rose or general-purpose fertilizer to power that first flush of growth. A seasonal feeding as the year goes on keeps the flowers coming, and this easygoing shrub asks for nothing more.
Pruning
Its pruning needs are refreshingly 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 coax out fresh growth. Deadheading is entirely optional, since the plant tidies itself, though snipping spent blooms can speed the next flush.
Repotting
Grown in a container, this rose rarely needs moving, but keep an eye out for roots circling or pushing out the drainage holes, water running straight through, or growth that stalls. Any one of those is your cue to move it up to a larger pot.
Size & spacing
The shrub eases into a rounded shape around 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 elbow room so air moves freely and the canes never crowd one another.
When to plant
This is a hardy shrub that comes through winters as cold as -20°F (-29°C), so it stays out in the garden all year in zones 5 through 9. Set it out in spring once the last frost has passed, and you can look forward to a repeat show of bloom from June until frost finally closes the season.
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
You will be glad to hear Knock Out roses sidestep most of the trouble that dogs other roses, so hiccups are few and far between. The one exception to watch for is rose rosette disease, which is fatal and worth catching early. Match what you are seeing below before you do anything.
Reddened shoots bunched like a broom and bristling with soft thorns
Take a breath, because this one is uncommon, but it helps to know it. What you are seeing is rose rosette disease, a virus carried by a mite too tiny for the eye, and it is the single trouble that can end a Knock Out. Fresh canes flush an odd bright red and bunch into a broom shape studded with soft, bendy thorns. Sadly there is no saving it, so lift the whole plant with its roots, seal it in a bag, and throw it away so nearby roses stay clear.
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
Foliage nibbled to lace and blooms left ragged in high summer
If the leaves look like green lace and the blooms are gnawed, Japanese beetles are almost always behind it, munching the soft tissue between the veins and chewing into the open flowers. The easy fix is to knock them into a jar of soapy water early in the morning, while the chill still keeps them slow. Try not to worry, since this shrub is sturdy and takes light nibbling in stride, so you only need to step in if aphids, thrips, or mites gather on the new growth too.
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
Dark blotches on foliage that yellow before dropping
Those dark marks are black spot, a fungus that acts up in warm, damp weather, but rest easy, since the Knock Out series was bred to resist it and a serious case is unusual. You will see round black blotches with feathery edges on the top of a leaf, and that leaf soon yellows and drops. Gather the fallen leaves and bin them, open the shrub up so air moves through, and pour water at the base to keep the foliage dry.
Fix:
- Remove and dispose of fallen infected leaves
- Improve air circulation and avoid wetting foliage when watering
Toxicity
Here is reassuring news for pet owners and parents: true roses are safe company. 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 nosy pet or prick a bare hand at pruning time.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
You can relax around a curious cat, since this rose will not poison one. The thorns are the only worry, as they might scratch an inquisitive nose or paw, and a cat that gulps down a lot of woody stem may feel a little queasy.
Dogs None
There is no poisoning risk for dogs with this rose, so no need to fret. Just mind the thorns, because a dog that chews the canes can prick its mouth, and a large mouthful of stem sits heavy and hard to digest.
Horses None
The ASPCA lists it as non-toxic, so a horse nibbling the leaves or petals comes to no harm at all. Keep the sharp thorns in mind and you are set.
Rabbits None
Rabbits can happily nibble the leaves and petals with nothing to fear. A thorn can scratch, though, so offer them a smooth, thornless length of stem for a kinder browse.
Livestock None
Cattle, goats, and sheep may browse the foliage safely with no poisoning to worry about. The thorns are the lone catch, and most animals just graze gently around them.
Birds None
Nothing on this rose will harm a bird, and plenty of them love the shelter those thorny canes give. Better still, the hips that form after the flowers make a welcome winter meal.
People None
Roses are gentle company for people, and the petals and hips are both edible. The thorns are the one thing to handle with care, so slip on gloves when it is time to 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 a single rose but a small, welcoming family, with selections that change up the flower color, the number of petals, and the size of the shrub. These are the ones you are most likely to meet.
Knock Out (Rosa 'Radrazz')
This is the one that started it all, breeder William Radler's original 1999 to 2000 introduction with single cherry-red blooms, and every other rose in the series traces back to it.
Double Knock Out
If you love a fuller flower, this form in the group opens double, many-petaled blooms.
Pink Knock Out
For anyone who prefers a gentler shade than the original red, this is the pink-flowered pick of the series.
Rainbow Knock Out
A smaller choice that greets you with coral-pink blooms lit by a soft yellow eye at the center.
Petite Knock Out
When space is tight, this compact, miniature-scale form was bred just for small beds, edges, and containers.
How to propagate
Cuttings root willingly enough, but there is a legal wrinkle you will want to know about 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
You can take cuttings from softwood or semi-hardwood growth in late spring through summer, and with a little patience they root over several weeks and settle in across a full season. There is one thing to know before you begin. This cultivar is patented under US Plant Patent PP#11836, which means propagating it to sell or hand out is legally off-limits while the patent still holds.
Myths
Knock Out roses shrug off any disease and never fall ill.
It is true they live up to their reputation against black spot and powdery mildew, brushing off the fungal woes that trouble older roses. Even so, they are not untouchable. Rose rosette disease, a fatal virus with no cure, strikes them the same as any other rose, so keep a friendly eye out for the red, broom-like growth that tells you it is there.
Knock Out roses won't keep blooming unless you deadhead them.
Happily, they clean themselves, letting go of spent blooms on their own and reblooming from spring to frost without a bit of help from you. Clipping off the old flowers only nudges the next wave along sooner, so think of it as a treat you can offer, never a duty.