Commonly known as a mosquito plant, Pelargonium x citrosum is actually a cross-bred scented geranium. It reaches an average height of 2 to 3 feet and spreads to about the same diameter. The lemony scent is similar to citronella, a mosquito repellent oil derived from a tropical Asian grass, Cymbopogon nardus. The pelargonium mosquito plant thrives in U.S. Department of Agriculture plant hardiness zones 8 to 10, and it is a perennial evergreen in most areas of zones 9 and 10. The lacy leaves of these drought-tolerant plants provide deep textural interest in xeriscaped gardens as well as a fresh aroma.