Cosmos 'Purity' is a well-named newer hybrid that selects the already-popular "great white" from the old mixtures, and presents it on a plant growing only 3 to 4ft. tall.
Like all the other Cosmos varieties, it's a snap to grow from seed. From June to October the large, graceful, saucer-shaped flowers up to 10cm (4in) or more in diameter are handsomely offset by the masses of mid-green feathery foliage.
They are fantastic as a blooming screen, or a background for shorter plants and are an excellent addition to the cutting garden. Cosmos is one of the best nectar plants for attracting bees and butterflies to the garden and the flowers are perfect for pressing.
A grand stand of this garden classic in late summer can provide months of long-stemmed cut flowers for a whole neighbourhood and there's nothing like baskets of clear white Cosmos for weddings.
Flowering in just fourteen weeks from sowing, they are very easy to grow, disease free and tolerant of poor soil, heat and humidity. They are an excellent "no fuss" annual that will thrive on minimal care and a perfect choice for children or the less experienced gardener.
Sowing: Sow indoors March to April, or sow outdoors April to May
Sow indoors in early spring three to four weeks before planting outside, alternatively, the seed can also be sown directly where they are to flower in mid to late spring. Keep soil moderately moist during germination, which takes around 7 to 10 days at 20 to 30°C (68 to 86°F)
Use well drained soil and cover to a depth of 3mm (1/8in). When large enough to handle, transplant the seedlings into small pots to grow on. Acclimatise to outdoor conditions for 10 to 15 days before planting out after all risk of frost 15cm (6in) apart.
Prepare the ground well and rake to a fine tilth. If sowing more than one annual in the same bed, mark the sowing areas with a ring of sand and label. Sow 1mm (1/18th in) deep in rows 30cm (12in) apart.
Sow seed sparingly or they will choke out other seedlings.
The seedlings will appear in rows approx 6 to 8 weeks after planting and can be easily told from nearby weed seedlings. Thin the seedlings out so they are finally 30cm (12in) apart. Carefully replant thinned plants.
When the seedlings have three pairs of leaves, pinch out the tips, leaving at least one pair of leaves.
Only water in an extended drought and do not apply large doses of fertiliser as flowering will be suppressed.
Stake the taller varieties with a single or tripod of canes and some twine. Cosmos foliage is finely-cut into threadlike segments. When flowering, the taller varieties may become top heavy. This problem is alleviated when grown in groups, as the bi-pinnate leaves interlock, and the colony supports itself.
Deadhead to prolong flowering and encourage new flower buds. At the season's end, don't be too quick to pull up withering cosmos plants. Birds (particularly gold finches) love to snack on their seedheads in autumn, and the seeds that they miss may drop to the ground and reward you the next year by sprouting into a whole new crop.
Cosmos is a cut-and-come-again bloomer, meaning that the sooner you cut the blooms, the quicker new buds will pop up to replace them. The blooms appear so profusely that you'll still have plenty of colour in the garden after you've picked your flowers. If you sear the stem end in boiling water for twenty seconds they will last seven to ten days in the vase.
Cottage/Informal Gardens, Flowers Borders and Beds. Container Planting.
Cosmos have been reassuring gardeners ever since the 1930s, when breeders first coaxed cosmos to bloom earlier than the native Mexican species. Since then the flower-growing public has been hooked.
Like many of our warm weather annuals such as marigolds, Cosmos originated in Mexico and South America. Spanish priests grew cosmos in their mission gardens in Mexico. The evenly placed petals led them to christen the flower "Cosmos", derived from the Greek kosmos, the word for harmony or ordered, or balanced universe. From this we also get the common name of "The Mexican Aster".
The species name is from the Latin pinnatus meaning “with leaflets arranged in opposite pairs. So bipinnatus means “twice-pinnate”
Synonym Cosmea bipinnata.
- Additional Information
Seed Form Natural Seeds per gram 150 seeds / gram Family Asteraceae Genus Cosmos Species bipinnatus Cultivar Purity Synonym Cosmea bipinnata Common Name The Mexican Aster Other Common Names Aka Cosmos 'Sonata White' Hardiness Half Hardy Annual Flowers Pure White Natural Flower Time June to October Height 90 to 120cm (36 to 48in) Spread 45cm (18in) Position Needs full sun to flourish Soil Lean, well drained, sandy soils. Germination 7 to 10 days at 20 to 30*C (68 to 86°F)