Sunflowers (Helianthus annuus) are annual plants native to North America that grow extraordinarily well in Colorado. This plant can withstand light frosts, and so is an excellent choice for early planting if you just can't wait to get started with your garden. Sunflowers track the sun during their bud stage through a natural phenomena called "heliotropism," by which motor cells in the stem just below the bud cause the head to follow the sun as it moves from east to west. It returns to the eastward orientation at night. In later stages of the flower's life, the stem thickens and the sunflower ceases movement and faces only eastward. One to numerous blooms (depending on which of the 60 species you plant) start bursting mid- to late-summer and last through the fall. The yellow, orange or bronze heads are made up of hundreds of tiny flowers called florets. Here are some tips for planting sunflowers if you live in Colorado.
Choose drought-resistant flowers to ensure healthy plants if you live on Colorado's Front Range or in any of its other drier areas (most of the state). Sunflowers are native to high plains and are a dry-land crop that has roots that extend as far as 6 feet into the soil (see Resources below).
Sow seeds 1½ inches deep and 6 to 12 inches apart in full sun and soil that is well drained and lean (such as clay loam). Place them next to annuals, perennials or herbs.
Thin the plants as they begin to pop out of the ground by snipping them off at the base. Don't pull them out of the ground, or you may uproot neighboring plants.
Water the plants. Sunflowers will grow almost anywhere with minimal watering, but they should occasionally be watered deeply.
Protect the plants. Sunflowers have few enemies, and diseases such as rust can be avoided if you choose a rust-resistant seed and rotate the plants so the disease doesn't establish itself in the soil.