Cosmos is the airy, effortless, romantic annual that gardeners reach for when they want a long summer of bloom with almost no work.
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Cosmos is the airy, effortless, romantic annual that gardeners reach for when they want a long summer of bloom with almost no work. On tall, slender stems above a haze of fine, feathery foliage, it carries simple, elegant, daisy-like flowers — most often in white, pink, and crimson — that nod and shimmer in the slightest breeze. Cosmos is one of the easiest plants to grow from seed, it flowers tirelessly from midsummer to frost, it is a favorite of bees and butterflies, and it makes a wonderful cut flower. Its single, gardener-friendly quirk: do not grow it in rich soil or feed it, or you get a forest of leaves and very few flowers.
Cosmos is native to the Americas, especially Mexico and the southern United States, where its ancestors grow in warm, sunny, open scrub and meadowland — often in poor, dry soil. (The Spanish missionaries who named it saw harmony and order in its evenly placed petals — "cosmos.") This origin in lean, sunny, warm conditions explains everything about its care, above all its dislike of rich soil. The most popular garden type is Cosmos bipinnatus; the orange-and-yellow Cosmos sulphureus is a related, more heat-loving species.
Cosmos is a tall, airy, branching annual, typically 60–150 cm tall (dwarf varieties are more compact). Its foliage is finely divided, feathery, and almost fern-like, giving the whole plant a light, see-through quality. The flowers are borne singly on long, wiry stems — broad, flat, daisy-like blooms with a ring of (usually) eight petals around a yellow center, in white, every shade of pink, and rich crimson, plus modern picotee, double, and rolled-petal forms. The effect in a border is soft, loose, and gracefully informal.
Full sun — cosmos needs at least six hours of direct sun for sturdy growth and free flowering. In shade it grows leggy and flowers poorly. A spot with some shelter helps protect the tall, slender stems from wind.
Poor to average, well-drained soil — and this is the key point. Cosmos evolved on lean ground; rich, fertile soil produces tall, lush, leafy plants with very few flowers. Do not improve the soil for cosmos.
Water to establish and during prolonged dry spells; once growing, cosmos is fairly drought-tolerant. Avoid waterlogging.
Do not feed. This is the single most important rule for cosmos. Feeding — especially with nitrogen — gives masses of feathery foliage and almost no flowers. Lean, hungry conditions are exactly what makes cosmos bloom.
Cosmos is a frost-tender annual — killed by the first frost and grown fresh from seed each year. Sow or plant out only after the danger of frost has passed.
Cosmos is very easy from seed. Sow directly outdoors after the last frost where the plants are to grow, or start in pots indoors a few weeks earlier and plant out after frost. Germination is fast and reliable. Cosmos often self-seeds, returning the following year — though garden hybrids may not come true. Successional sowing extends the display.
Cosmos (Cosmos bipinnatus and related garden species) is generally regarded as non-toxic / low-toxicity and is considered safe for cats, dogs, horses, and humans — it is not a recognized poisoning hazard and is widely grown in family and wildlife gardens. (Note: the unrelated "chocolate cosmos," Cosmos atrosanguineus, is a different, tuberous plant.) A safe, pollinator-friendly, family-friendly garden flower.
Pros
Cons
Not ideal for shady gardens, rich well-fed borders (it will not flower), or gardeners wanting a permanent perennial.
Why does my cosmos have lots of leaves but no flowers? This is the classic cosmos problem, and the cause is almost always soil that is too rich, or feeding the plant. Cosmos evolved on poor ground — rich, fertile conditions and fertilizer push leafy, feathery growth at the expense of flowers. Stop feeding it, and grow it in lean soil.
Should I feed cosmos? No — do not feed cosmos. Feeding produces masses of foliage and very few flowers. Lean, hungry, poor soil is exactly what makes cosmos bloom well.
How do I keep cosmos flowering all summer? Deadhead regularly, or cut flowers for the vase — removing spent flowers before they set seed keeps cosmos blooming continuously. Pinching young plants for bushy growth, and full sun, also help.
Is cosmos easy to grow from seed? Yes — cosmos is one of the easiest annuals from seed. Sow directly outdoors after the last frost, or start indoors a few weeks earlier; germination is fast and reliable, and plants often self-seed for the following year.
Are cosmos safe for pets? Yes — garden cosmos is generally considered non-toxic to cats, dogs, and horses, and is a safe, pollinator- and family-friendly plant.