In the Garden: Cosmos: A Worthy Annual

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By Charles Kidder

Spanish priests in colonial Mexico gave the name Cosmos to a flower that possessed an orderly, symmetrical shape, in honor of the (supposedly) harmonious and orderly universe. They could just as easily have given the same name to the sunflower, but perhaps they saw the cosmos first. And given our current knowledge, I dare say that we no longer consider the universe to be quite so harmonious.

With the same common and scientific name, the genus Cosmos consists of some three dozen species, all native to the Americas, but naturalized through much of the tropical and warm temperate world. Along with dandelions, sunflowers, asters, etc., they are part of the very large family known currently as the Asteraceae. Formerly known as the Compositae, the “flower” in fact consists of many small flowers: each individual petal is a flower, as is each tiny dot in the disc at the center of the inflorescence.

Most cosmos species are annuals; indeed, all are so in our climate. And here we come to one of its most worthy attributes, at least in the mind of this lazy gardener. To “plant” cosmos, simply throw the seeds on the ground. If you’re feeling energetic, you could tamp them lightly with your foot or scratch them in with a rake. Last fall I just sprinkled the seeds around my garden, and in late spring they started popping up. (Germination doesn’t occur until the soil warms up to about 75 degrees, so be patient.) Assuming that something doesn’t go awry, this year’s crop of cosmos will seed into the garden and get it ready for next year.  The obvious message here: don’t be in a hurry to “clean up” your garden. When you do clean up, sprinkle some of the black, spiky seeds onto sunny places. Or better yet, just lay the whole stalk on the ground.

Two species of Cosmos are commonly available for sale in our area. The wild Cosmos bipinnatus appears with pink, purple and white flowers, often all occurring in the same population. Although almost all varieties of C. bipinnatus have flowers in this color range, a new cultivar ‘Xanthos’ has appeared with pale yellow blooms. The 4’ to 5’ stature of the species can lead to floppy plants if they don’t have something to lean on, but cosmos actually has a strategy to deal with that. The frilly foliage of neighboring plants can interlock, providing rigidity to the whole group. If you prefer shorter plants, dwarf varieties reaching only one to two feet in height are available. Some of these varieties are also listed as “early” types, with flowers starting earlier in the season. (Hailing from tropical latitudes with shorter summer days, cosmos generally bloom for gardeners in temperate latitudes in late summer into fall.)

The sulfur cosmos (C. sulphureus) can grow even taller than bipinnatus; the straight species can reach seven feet, although dwarf varieties are available. As the name implies, sulfur cosmos often has yellow flowers, but orange and orangey-red varieties are also common.

All cosmos want full sun and do not require particularly rich soil. In fact, overly fertile soil will just lead to tall, floppy plants, so throw the seeds on some of the nastier corners of your garden. Shrubs or tall ornamental grasses can provide support, as long as the cosmos gets sufficient sun.  You can prolong bloom by deadheading, but I wouldn’t advise the tedium of snipping off individual flowers. Just wait until they’re nearly spent and whack off the tops of the plants with shears. Or if you want flowers for a vase, cut them just as the petals unfold, and they should be good for 7-10 days.

A couple of other notes about cosmos:  Chocolate cosmos (C. atrosanguineus) is a species often described as a perennial, but only in zones 8 (or 9) and warmer. Producing sterile seeds, it must be propagated from root divisions. Depending on whom you believe, the dark red/chocolate-brown flowers produce some degree of chocolate fragrance. And speaking of food, what about a cosmos that you can eat? The foliage of Cosmos caudatus (Ulam Raja, or King’s salad) is commonly eaten raw in Malaysia. I couldn’t find any source for seed, but you might have better luck.

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Now for an update on abelias.  In the June column I mentioned that two of our Abelia ‘Radiance’ plants had produced long shoots that stuck up oddly from the rest of this low-growing cultivar. As a test, I cut one plant down to the main structure, and left the other one alone. As of this writing—early October—the uncut plant still looks rather odd (see picture).  The pruned shrub looks more graceful, so I expect to cut the others back next spring.

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