Double Red Knockout RoseDouble Red' is grown for its cherry red double (twice the petal count of 'Red' Knock Out) flowers that appear in clusters in great profusion from spring until frost. Garden writers tell us 'Double Red' Knock Out differs from 'Red' Knock Out in three ways: Even richer cherry red flowers, its flowers are "double" rather than single to semi double and it matures smaller & more compact, at 3 4' rather than 4 5'.