For the beginning gardener, cosmos are an ideal plant. There are many different species of cosmos, but just about all of them germinate very quickly, grow very rapidly, and are hardy enough to tolerate an early spring frost and the summer's blazing sun. Most cosmos grow to be anywhere from 2 to 7 feet (60 to 215 centimeters) tall -- depending on the species -- and tend to be placed in the rear of garden arrangements.
There are two predominant species of cosmos in the U.S. South -- cosmos sulphureus (yellow cosmos) and cosmos bipinnatus (pink cosmos). Although cosmos may perform better in drier, hotter environments, they will grow just about anywhere they can consistently receive a day full of sunshine. In fact, cosmos lavished with too much water and shade become frail and bloom inconsistently [source: The Gardener's Network].
Yellow cosmos grow to be between 2 to 4 feet (60 to 120 centimeters) tall with flowers of red, orange or yellow, and long, narrow green leaves. Yellow cosmos are traditionally planted in spring, usually raked into the soil, and will germinate once the soil reaches a temperature of 70 degrees Fahrenheit (21 degrees C). Yellow cosmos only take a few weeks to germinate, and will bloom very quickly after. Once the flower has bloomed, yellow cosmos require little watering or maintenance. If planted in fertile soil outside of its native climate, yellow cosmos will grow very lanky and tall. Likewise, using fertilizer on yellow cosmos will produce a much leafier, taller plant.
Pink cosmos share many of the same growing tendencies as yellow cosmos, but are especially popular in the sandier soils near the Gulf of Mexico and the Atlantic Coast. Pink cosmos range in height from 1 to 7 feet (30 to 215 centimeters) tall depending on the species and growing conditions, with flowers white, pink, rose or red in color. Though they both thrive in similar climates and soils, pink cosmos are generally not as hardy as yellow cosmos, and often require stakes to hold their stems upright. Pink cosmos are often used in grassy, meadow-like gardens, quite often because their nectar is known to be one of the best for attracting butterflies [source: Scheper].