Shrub · Rosaceae
Knock Out Rose
Rosa
Give it full sun and a quick yearly prune, and the Knock Out just keeps blooming from June to frost.
Full sun
Every 7–14 days
USDA 5–9
3–4 ft · 0.9–1.2 m
Overview
So what makes the Knock Out rose such a big deal? Breeder William Radler wanted a rose that would flower all season without all the spraying and babysitting the old roses needed, and his original 'Radrazz' showed up in 1999. It's part of the rose family, but think of it as a tough, easygoing landscape shrub rather than a fancy show rose.
The real draw is how little it asks for. It's self-cleaning, which means it drops its old flowers by itself, and it keeps reblooming from June right up to frost without any deadheading. It also stands up to black spot and powdery mildew, the fungus that scared a lot of folks off roses, and once its roots settle in it barely notices a dry spell.
And it won't take over the yard either, since it holds to a tidy mound of about 3 to 4 feet (91 to 122 cm) in most gardens. That makes it easy to tuck into a foundation bed, run as a low hedge, or drop in a big container, and you get a long stretch of bloom to enjoy all summer and fall.
Care
The short version: give it full sun, well-drained loam, and a good deep soak while it settles in, then only water during dry stretches once it's established. Mulch around the roots, feed it in spring, and cut back about a third of the oldest canes each spring to keep it open and blooming.
Light
This rose blooms best in full sun, six to eight hours a day. It'll get by in partial shade too, but expect fewer flowers and a looser, leggier shape if it's not getting enough light.
Water
Water it deeply and often right after planting until the roots grab hold, then you can back off, because it's drought tolerant once established. A good soak every 7 to 14 days during a dry stretch does the job, and about 3 inches of mulch kept off the stem helps hold the moisture in.
Soil
Give it well-drained loam with a pH somewhere between 6.0 and 7.0. It's not picky about the soil itself, but drainage really matters, so mix some compost into heavy clay before you plant.
Temperature
It's a genuinely cold-hardy rose, handling winter lows near -20°F (-29°C) and summer heat up to 100°F (38°C). That covers most temperate gardens without any special fuss.
Humidity
Regular outdoor humidity is fine, so there's no number you need to chase. What matters more is airflow, since crowded, stuffy air is what gives the odd fungal spot a chance to take hold.
Feeding
Feed it once in spring with a balanced rose or general-purpose fertilizer to power that first burst of growth. A seasonal feeding through the year keeps the blooms coming, and this laid-back shrub doesn't ask for anything more.
Pruning
It barely needs pruning at all. In spring, use the renewal method and cut about a third of the oldest canes right down to the soil line to keep it open and push out fresh growth. Deadheading's optional since it cleans itself, but snipping the spent blooms can hurry the next flush.
Repotting
In a pot it hardly ever needs moving, but keep an eye out for roots circling or poking out the drainage holes, water running straight through, or growth that just stalls. Any of those, and it's time to bump it up to a bigger pot.
Size & spacing
The shrub settles into a rounded shape around 3 to 4 feet (91 to 122 cm) tall and about as wide. Give each one that same 3 to 4 feet (91 to 122 cm) of space so air can move and the canes don't get crowded.
When to plant
This is a hardy shrub that shrugs off winters as cold as -20°F (-29°C), so it lives in the garden all year in zones 5 through 9. Just plant it in spring once the last frost's gone, and you'll get a repeat show of bloom from June until frost finally calls it a 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
Good news: Knock Out roses skip most of the drama that comes with other roses, so you won't run into much. The one thing to really watch for is rose rosette disease, which is fatal and worth catching early. Take a look below and match the symptoms before you do anything.
Clustered red shoots that look like a broom, loaded with soft thorns
Seeing weird red canes bunched up like a broom? That's rose rosette disease, a virus a mite too small to spot carries around, and it's the one thing that can actually kill a Knock Out. The giveaway is that bright red new growth crowding together and covered in soft, bendy thorns. There's no fixing it, so pull the whole plant, roots and all, bag it up, and toss it before the mite hops over to your other roses.
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
Lacy, chewed leaves and tattered flowers when summer peaks
If the leaves look like green lace and the flowers are all chewed up, it's usually Japanese beetles, munching the soft bits between the veins and going after the open blooms. The easiest trick is to flick them into a jar of soapy water first thing in the morning, when they're still too cold to fly off. This shrub is tough and won't mind a little nibbling, so there's no need to fuss unless aphids, thrips, or mites also start piling onto the new growth.
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-spotted leaves that go yellow and drop off
Those dark blotches are black spot, a fungus that shows up in warm, wet weather, though honestly you won't see much of it since the Knock Out series was bred to shake it off. The marks are round and black with feathery edges on the top of the leaf, and the leaf yellows and drops soon after. Just rake up the fallen leaves and bin them, open the plant up so air can move through, and water at the base so the leaves stay dry.
Fix:
- Remove and dispose of fallen infected leaves
- Improve air circulation and avoid wetting foliage when watering
Toxicity
Got pets or little kids around? You're in the clear, because true roses are safe. Every part of this rose is non-toxic to cats, dogs, horses, and people, and the petals and hips are actually edible. The only real thing to watch is the thorns, which can scratch a curious nose or prick a bare hand when you're pruning.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
No poison worries with a cat here. The thorns are really the only thing to watch, since they can scratch a nosy nose or paw, and a cat that swallows a bunch of woody stem might get a bit of a tummy ache.
Dogs None
Nothing about this rose will poison a dog, so no stress there. Keep an eye on the thorns though, because a dog chewing the canes can jab its mouth, and a big wad of stem isn't easy to digest.
Horses None
The ASPCA calls it non-toxic to horses, so a horse can munch the leaves or petals and be totally fine. It's just those sharp thorns you'll want to keep in mind.
Rabbits None
Rabbits can nibble the leaves and petals no problem. A thorn can still scratch though, so a smooth, thornless bit of stem makes for a gentler snack.
Livestock None
Cows, goats, and sheep can browse the foliage without any poisoning. The thorns are the only snag, and most of them just graze right around them anyway.
Birds None
There's nothing here to poison a bird, and plenty of them actually love the cover those thorny canes give. Even better, the hips that come after the flowers make a nice winter snack.
People None
Roses are perfectly safe around people, and you can even eat the petals and the hips. The thorns are the only catch, so pop on some gloves when it's 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
Here's the thing: Knock Out isn't just one rose, it's a little family, with picks that change up the flower color, how many petals you get, and the size of the shrub. These are the ones you'll bump into most.
Knock Out (Rosa 'Radrazz')
This is the one that kicked it all off, William Radler's original 1999 to 2000 introduction with single cherry-red blooms, and every other rose in the series came from it.
Double Knock Out
Want a fuller flower? This double-flowered form in the group gives you plenty more petals.
Pink Knock Out
This is the pink one in the series, perfect if you'd rather have a softer color than the classic red.
Rainbow Knock Out
A smaller pick that opens up coral-pink blooms with a cheerful yellow eye right in the middle.
Petite Knock Out
Short on space? This compact, miniature-scale form was made for small beds, edges, and pots.
How to propagate
Cuttings root pretty easily, but there's a legal catch you'll want to know about before you start a new plant from one you already have.
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 anytime from late spring through summer, and they'll root over a few weeks and get comfortable across a whole season. Here's the catch though. This cultivar is patented under US Plant Patent PP#11836, so propagating it to sell or hand out is off-limits by law while that patent's still in force.
Myths
Knock Out roses can't catch any disease at all.
Sure, they live up to the hype against black spot and powdery mildew, brushing off the fungus that bugs older roses. But immune? Not quite. Rose rosette disease, a fatal virus with no cure, gets them just like it gets any other rose, so keep an eye out for that red, broom-like growth that tips you off.
Knock Out roses stop flowering if you don't deadhead them.
Nope, they tidy up after themselves, dropping the old blooms and reblooming from spring to frost without any help from you. Snipping off the spent flowers just moves the next round along a little faster, so it's your call, not a chore.