In a range of colours and flower shapes, Cosmos are one of the most versatile mid-height annuals for a sunny spot in borders or pots. They're loved by pollinators, with their large, daisy-like blooms. With attractive ferny leaves acting as a perfect foil for the blooms, they're one of the nation’s best-loved half-hardy annuals.
Florists value them for their long vase life, foliage and the sheer variety of colours, from white, pink, yellows, reds, bicolours and picotee edgings.
Flowers range in shape from the shell-like bipinnatus Sea Shells Mixed, to the fully double Snow Puff. It's the classic open single varieties with yellow centres that are the cottage garden - and bees and butterflies - favourites. Look for the ever-popular white Purity, Sensation Dazzler Crimson Red, Colour Mix and Candy Stripe.
Flowering from summer right through to the first frosts, they're the ideal plants to see your garden right through to the end of the season. Read more
How to grow Cosmos
Sow indoors from February-April, in a propagator at 15°C/60°F, on good-quality, moist seed compost at a depth of 0.5cm/1/4in. After germination, grow on in good light to avoid legginess and thin out into modules or small pots at the 2-4 leaf stage. Harden off young plants over a period of a couple of weeks and plant out from late May, or after the last frost. At this time, pinch out the growing tips to encourage more flowers. Space plants 30cm/12in to 45cm/18in apart, depending on final height.
Cosmos can also be sown outdoors where they are to flower from April-May. Grow in fertile, moist, but well-drained soil in full sun. Mulch to preserve moisture. Deadhead flowers regularly to prolong the flowering season. By leaving a few seed heads to ripen at the end of the season, some Cosmos may self-seed for the following year. If planting in pots use compact varieties, plant several in a large container in good-quality compost with added water-retaining gel and a slow-release fertiliser.
Did You Know?
Cosmos are natives of Mexico and the southern USA, hence one of their common names, the Mexican aster. Show less