Cosmos

Cosmos are freely flowering annuals that are easy to grow by sprinkling some seeds in the garden after any danger of frost has passed. These quintessential cottage garden flowers reach full maturity in about two months. Cosmos can be slower to germinate, but it blooms quickly after that and continues to flower through the fall. The flowers sit atop long slender stems and form a cloud of attractive color all summer that attracts bees, butterflies, and birds to your garden. Cosmos flowers look a lot like daisies. They come in a broad range of colors, with more cultivars developed every year. The leaves grow opposite on stems and are deeply lobed, pinnate, or bipinnate and feathery-looking depending on the type. If you plan to have cosmos and live in the southern U.S., consider keeping them as potted plants since they tend to be invasive there.

Cosmos grow easily in beds and make great cut flowers. When established, the plants can handle drought, poor soil conditions, and general neglect. They even self-sow. This is a truly low-maintenance plant.

While some pests, like aphids, flea beetles, and thrips feed on cosmos, they’re easy to control with a strong spray of water or insecticidal soap. Aster yellows, bacterial wilt, and powdery mildew may also affect cosmos. Space plants accordingly to ensure good airflow to avoid diseases.

Taller varieties look good in the middle or rear of the border with goat’s beard, coneflowers, and black-eyed Susans. Shorter varieties make very colorful, airy edging plants.

Light

For the best flowering, choose a site that gets full sun. Cosmos will grow in partial shade but will have fewer blooms and be less vigorous when planted in shady areas. These plants will also thrive under uninterrupted full sun in the hottest conditions, much like their native habitat: the arid regions of Mexico and Central America.

Soil

Cosmos plants prefer a neutral soil with a pH of 6.0 to 8.0, although they will grow in poor soil where many flowering plants languish. They perform best in medium moisture, well-drained soils, but they will perform adequately in dry soils. Avoid planting in a rich soil; it can cause the plants to get too tall and flop over. You can prevent drooping by staking the plants or growing them close to other plants that can support them.

Water

Once established, you will not need to water your cosmos plants unless there is a prolonged drought. Where water is limited, these are the last plants that require irrigation.

Temperature and Humidity

Hot weather is ideal for cosmos, and they thrive in any humidity level.

Fertilizer

Fertilizing can negatively impact cosmos. Cosmos can handle poor soil. Too much fertilizer can often lead to strong plants with lots of foliage but few blooms. Unless your plants seem to be struggling, these plants do not need fertilizer.

Types of Cosmos

There are over 25 species of cosmos. However, three species are most commonly used in gardens and landscaping. Cosmos sulphureus is native to Mexico, Central America, and northern South America. With golden yellow blooms, it is very drought tolerant and loves hot weather. The plant grows 2 to 6 feet tall and comes in double and semi-double flowers. Some of the more recent cultivars tend to be shorter, more orangy, and with smaller flowers.

Cosmos bipinnatus are colorful daisy-like flowers that come in white, pinks, reds, and orange. At 1 to 4 feet in height, they are shorter than C. suphureus and are available in several popular hybrid series. Although they are not quite as heat tolerant as C. sulphureus, C. bipinnatus will grow well in just about any sunny space.

Chocolate cosmos are a separate species: Cosmos atrosanguineus. The dark red flowers smell like chocolate. This perennial is hardy to USDA zone 7, but it is higher maintenance than annual cosmos. Like dahlias, it grows from tubers.