Rose
Double Knock Out Rose
Rosa 'Radtko' · Rosaceae
Also called: Double Knockout Rose
Double Knock Out Rose (Rosa 'Radtko') is a moderate-water rose well suited to Tucson and the low desert. It thrives in full sun, with a fast growth rate.
Double Knock Out Rose at a glance
- Water use
- Moderate (established)
- Sun
- Full sun (6+ hours); in Tucson, filtered or afternoon shade helps reduce summer stress and sunburn.
- Mature size
- 3-4 ft tall and 3-4 ft wide.
- Growth rate
- Fast
- Bloom
- Cherry-red to bright pink-red double (more petals, ~18-24) blooms., Nearly continuous spring through fall; heaviest in spring and fall in Tucson, with reduced bloom in peak summer heat and winter dormancy.
- Cold hardiness
- Cold hardy to USDA zone 5 (about -20°F); fully hardy in Tucson with little to no frost protection required.
- Soil
- Well-drained soil amended with compost; improve Tucson caliche/alkaline soils for drainage and add iron to manage alkalinity.
- Native range
- Cultivated hybrid (Bill Radler, introduced ~2004); not native.
- Best used as
- Landscape shrub / mass planting, Hedges and borders, Low-maintenance color, Foundation plantings, Disease-resistant rose for hot climates
- Wildlife
- Attracts bees and pollinators; provides nectar. Watch for aphids and chili thrips in the low desert.
- Toxicity
- Non-toxic to humans and pets; thorns pose only physical injury risk.
How to grow Double Knock Out Rose in Tucson & the low desert
Watering
Water deeply 2-3 times per week in summer heat, weekly in spring/fall, every 10-14 days in winter. Use drip irrigation to 18-24 in depth and mulch 2-3 in to retain moisture and cool the root zone.
Fertilizer & nutrients
Fertilize monthly Feb-Oct with a balanced or rose fertilizer; add chelated iron to prevent chlorosis in Tucson's alkaline soils. Cease feeding by late October.
Pruning & care
Hard prune in late winter (mid-January to mid-February), reducing by one-third to one-half. Self-cleaning, so deadheading is optional; light shearing after bloom flushes keeps it tidy and promotes rebloom.
Notes
The double-flowered version of the original Knock Out, offering a fuller bloom with the same outstanding disease resistance and heat tolerance, making it a top low-maintenance rose for Tucson. Plant bare-root in winter or container-grown in fall. Monitor for chili thrips.
Sources: University of Arizona Cooperative Extension / Pima County Master Gardeners rose guides; AMWUA Landscape Plants for the Arizona Desert; American Rose Society guidance adapted for low desert