"Willing" is the word that comes to mind when I think of the cosmos clan. I have abused them beyond conscience, always to be rewarded with filigreed foliage and happy, dancing flowers. Last year, my Cosmos bipinnatus seedlings languished indoors far too long, but once I plopped them into the kitchen garden among the tomatoes and haricots verts, then proceeded to ignore them, they galloped up to 4 feet, producing masses of white, pink, lavender, and dark-red daisylike flowers until frost.
C. bipinnatus ranges in height from 20 inches to 5 feet and bears mostly large, single flowers, though 'Psyche' is often semi-double, and 'Seashells' has fascinating, rolled petals. Some varieties, such as 'Daydream' and 'Candy Stripe', are bicolored, with splashes, edges, stripes, or centers in the red-pink range contrasting with white. The 'Sonata' and 'Fairy Mix' selections are the most dwarf, at 20 inches. C. bipinnatus petals are thin and silky, catching light beautifully, while the stems are wiry, so these are dancing flowers in even a light breeze.
If you're looking for hot colors -- orange, red, yellow, gold -- you'll want to grow C. sulphureus. Sometimes called Klondyke types, these are not only brighter but generally shorter than their pastel cousins, have smaller, semi-double blooms, and foliage that's less lacy. Most of them are about a foot tall, with the clear, lemon-yellow 'Sunny Lemon Twist' reaching a bit over 2 feet. 'Ladybird Scarlet' is bright orange-red, and there is also orange and gold 'Ladybird'. 'Bright Lights' is a mix of yellow, gold, orange, and dark red; 'Red Crest' is reddish-orange.
Both C. bipinnatus and C. sulphureus are easy to grow from seed. They germinate quickly and can be sown directly into the ground with great success. If you're starting seeds indoors, wait until six to eight weeks before warm, settled weather is due. Outdoors, sow the seed after the danger of frost is past. Barely cover the seed with soil, either indoors or out, as they need some light to germinate. Cosmos will self-seed if you don't deadhead them. You can save the seed if you're so inclined, but the flowers won't always come true to type; fancy varieties often revert to the simple single-flower form.
As Mexican natives with a Greek name (derived from kosmos, meaning beautiful), cosmos love the sun, though they'll do fine in semi-shade in warmer zones. While they will repay you for good (but not overly rich) soil and regular watering, the sulphureus types especially thrive in stony or sandy, hot, dry conditions. Overfeeding or too much water may delay flowering. The taller varieties tend to sprawl, so they look better with some support and a bit of wind protection.
Cosmos will tolerate overcrowding, but they'll be happier spaced 1 to 2 feet apart, depending on their ultimate height. Mine have never had any problem with either pests or diseases.
Cosmos are great cut flowers, especially if you put them in warm water first, then transfer them to cool water after a few minutes. Keeping the flowers cut regularly, or deadheading the ones that escape you, will guarantee a long season of bloom.
You can find Cosmos in abundance at our North Bergen/Edgewater Store starting in June.
by Mary Morgan of Fine Gardening Magazine