rose mallow Rose Mallow is hibiscus moscheutos, often referred to as sea mallow swamp and swamp rose mallow. It is a deciduous hibiscus shrub that grows in cold regions. It is a salt marsh plant and grows up to 7 meters in height. The flowers are around 4 to 7 inches wide long with green, oval leaves. The flowers are mainly pink in color that deepens as they age. Rose mallows need full sun, well-drained, slightly acidic soil and plenty of water to grow.