Rose
Knock Out Rose
Rosa 'Radrazz' · Rosaceae
Also called: Single Knock Out Rose, The Knock Out Rose
Knock Out Rose (Rosa 'Radrazz') is a moderate-water rose well suited to Tucson and the low desert. It thrives in full sun, with a fast growth rate.
Knock Out Rose at a glance
- Water use
- Moderate (established)
- Sun
- Full sun (6+ hours); in Tucson, benefits from filtered or afternoon shade to reduce summer heat and sun scald.
- Mature size
- 3-4 ft tall and 3-4 ft wide (can reach 4 ft+ in Tucson with good care).
- Growth rate
- Fast
- Bloom
- Cherry-red to bright single (5-petal) blooms., Nearly continuous spring through fall; in Tucson blooms heavily in spring and fall, slows in extreme summer heat, and rests in winter.
- Cold hardiness
- Cold hardy to USDA zone 5 (about -20°F); very tolerant of Tucson winters. Minimal frost protection needed; foliage may brown in hard freezes but recovers.
- Soil
- Well-drained, organically amended soil; amend Tucson's caliche/alkaline soils with compost and ensure good drainage. Prefers slightly acidic to neutral pH but tolerates alkaline with iron supplementation.
- Native range
- Cultivated hybrid (introduced by Bill Radler, 2000); not native. Roses derive from Eurasian species.
- Best used as
- Landscape shrub / mass planting, Hedges and borders, Low-maintenance color, Foundation plantings, Disease-resistant rose for hot climates
- Wildlife
- Flowers attract bees and other pollinators; hips can feed birds. Susceptible to aphids and occasionally chili thrips in the Southwest.
- Toxicity
- Non-toxic to humans and pets; thorns can cause physical injury but no chemical poisoning.
How to grow Knock Out Rose in Tucson & the low desert
Watering
Water deeply and regularly: roughly 2-3 times per week in summer heat, less in spring/fall, and every 10-14 days in winter. Use drip irrigation, water to 18-24 in depth, and apply 2-3 in of mulch to conserve moisture and cool roots.
Fertilizer & nutrients
Feed monthly during the growing season (Feb-Oct) with a balanced or rose-specific fertilizer; supplement with iron/chelated iron to correct chlorosis (yellowing leaves) common in Tucson's alkaline soils. Stop feeding by late October to harden off before frost.
Pruning & care
Major prune in late winter (mid-January to mid-February in Tucson), cutting back by about one-third to one-half. Deadhead lightly through the season, though it is self-cleaning; shear lightly after each bloom flush to maintain shape.
Notes
Exceptionally disease-resistant (especially to blackspot) and low-maintenance, making it one of the best-performing roses for Tucson. Plant bare-root in January-February or container-grown in fall. Watch for chili thrips, an increasingly common rose pest in the low desert.
Sources: University of Arizona Cooperative Extension / Pima County Master Gardeners rose guides; AMWUA Landscape Plants for the Arizona Desert; Rosarian/American Rose Society guidance adapted for low desert