The fire - engine - red double blooms of 'Double Knock Out' keep coming until hard frost, and its new growth is a stunning burgundy red. Aptly named, this popular successor to 'Knock Out' is fuller and more floriferous, producing clusters of 2 1/2in, incandescent blooms with 18 - 25 petals. A hardy variety naturally resistant to black spot and other diseases and pests.