A Harem of Males

Phew, what a year 2020 was! Well, it’s over and, at least at this writing, things look hopeful for the future, at least from my perspective. Except if you live in a tropical or subtropical climate, there’s not much distraction from anything gardenwise, for now, so let’s take a close look at a plant no doubt sitting on many coffee tables and windowsills. Poinsettia. I’m not a big fan of their appearance, but I do like them as botanical curiosities.

Let’s share some botanical lore of this plant by setting your holiday poinsettia on a table in good light for a close look at its flowers. I say “close  ” because the flowers are not those large, red, leaf-like structures. The large, red, leaf-like structures are just that — leaves, albeit modified leaves called bracts. The bracts attract pollinating insects to the plant.

The actual flowers of the poinsettia, which are not very showy at all, originate within the small, greenish, cup-shaped structures you see above the bracts. These cup-shaped structures are “cyathiums.”
poinsettia cyathiums
Each cyathium contains a single female flower surrounded by a harem of males. Pluck a cyathium from the plant, take a sharp knife or razor, and slice it in half from top to bottom. A magnifying glass helps now. You’ll see that the inner wall of the cyathium is lined with numerous tiny flowers which, when the flower is mature, protrude up through the opening of the cup. These are all male flowers.

Look very carefully and you’ll also see a stalk attached to the very bottom of the cyathium, protruding up through the cup opening, and capped by what looks like a turban. That is the single, female flower, which, to promote cross- rather than self-pollination, emerges from the cyathium after male flowers begin to shrivel. Cross-pollination promotes genetic diversity for healthier plants. 

In addition to the male and female flowers, on the outside of the cyanthium is a single yellow gland that looks like the mouth of a fish poised to ingest food.
Cyathium close up
Next time a friend comments on the beauty of your poinsettia flower, take out a magnifying glass and closely examine a few cyathiums before looking up and agreeing nonchalantly.

Fool the Plant

Have you ever wondered how stores always manage to have blooming poinsettias for the holiday season? 

Poinsettia, along with chrysanthemums and most strawberry varieties, is a “short-day” plant. Short-days induce “short-day” plants to form flower buds. (In reality, plants are responding to long nights, but the phenomenon was originally thought to be daylength dependent, and the term “short-day” plants has stuck with us.) Poinsettia can be fooled into blooming at any time of the year merely by exposing it to artificially shortened days. 

To secure blooming plants for this past holiday season, poinsettias grown in large commercial greenhouse ranges were covered with a shade cloth so that they experienced 14 hours of darkness each “night” beginning around September. After 8 weeks of this treatment, they formed flower buds which became fully developed just before the holiday season.

You Do It

You can do this at home to make this year’s poinsettias bloom again whenever you want. Your poinsettias first will need a rest period. Loss of leaves and fading flowers indicate that your plants are entering dormancy. (Even tropical plants, such as poinsettia, do take a short, mild annual rest.) When the plants become dormant, move them to where it is cool. Water them infrequently, just enough to keep their stems from shriveling.

About April, the plants will be ready to start growing again. Cut the stems back to a few strong shoots, each about 6 inches long. Give the plants sun, warmth, and water. New shoots will push forth from dormant buds. When warm weather has settled, you can put the plants outside.

As temperatures cool in late summer, bring the plants indoors to a sunny window. Keep them away from cold drafts, which would cause their leaves to drop.

Now for the photoperiod treatment. Beginning three months before you would like the plants to bloom, make sure the plants get 14 hours of darkness each night. Moving them into a dark closet or covering them with a paper bag are convenient ways to do this.

The dark period each night must be uninterrupted. Even peek at them with a flashlight at midnight will have them acting as if they had a short night, instead of the needed long night.

After 8 weeks of the above treatment, move the plants back to their sunny window. Flower buds should be evident, and you should have blooming poinsettias within a month. If you want bloom for the holiday season next year, start the photoperiod treatment about the middle of September.


Poinsettia, Euphorbia pulcherrima, is a member of the Euphorbiaceae family, commonly called the Spurge family. A common characteristic of plants in this family — which includes Hevea braziliensis, tapped commercially to make rubber — is the milky sap they exude when cut. The sap has often been considered poisonous and was sometimes used medicinally as a purge (hence “spurge,” from the French word espugier, meaning to purge). But, as Philippus Aureolus Theophrastus Bombastus von Hohenheim, more commonly known as Paracelsus, wrote in the 15th century, “All things are poisons, for there is nothing without poisonous qualities. It is only the dose which makes a thing poison.”

In fact, the sap is only mildly poisonous to humans and other animals. It can cause a rash on the skin or mouth, and stomach upset. So go ahead and nick the stem of your poinsettia and see the milky sap exude. No need to touch it.

Red and Green for Winter

A Mexican Native Adapts to Pot

A recent snowfall draped the landscape in magic. The white blanket settled softly on every horizontal surface to create a harmony in white.

Still, I miss green. Even better than seeing some green plants would be to liven up that green with, from the opposite side of the color wheel, red. And even better still would be to have this red-and-greenery close at hand — indoors.

Three plants fill this bill well, and are easy-care houseplants.

The most obvious and common member of this clan is poinsettia. Poinsettia plantBreeding, manipulation of their greenhouse environment, and plant growth regulators have transformed this sporadically blooming native of Mexico into a compact plant bursting into large blossoms for Christmas in foil wrapped pots.

(Actually, the “blossoms” are not blossoms, but colored bracts, which are modified leaves. Peer into the whorl of bracts and you’ll see small, round, yellow cups, called cyanthiums in which inconspicuously reside the true blossoms.)

Poinsettia need not be a throwaway plant when the holiday season ends. The plant is easy to grow and, with just slightly more trouble, can be brought into bloom again this time next year. The plant is photoperiodic, meaning it blossoms after a period of exposure to short days. For poinsettia, that’s about a month of 12 hour, or less, days. That photoperiod begins about mid-September around here, so the plants could be left outdoors for the period as long as they’re not exposed to freezing temperatures. Or a plant could be moved in and out of a closet.

Although the photoperiod is spoken of in terms of length of day, length of darkness is what really matters. So each day’s dark period must be uninterrupted; no car headlights, table lamps, or even a flashlight.

If all this seems like too much trouble, just treat a poinsettia like any other houseplant. Photoperiod doesn’t stand alone in prompting flowers. Given good growing conditions, a poinsettia will still blossom — just not at Christmas.

Worth Having Even If It Does Come Late, or Early

Christmas cactus also offers red-and-greenery in winter, and is also photoperiodic. But not always. In a cool room, below 60°F., the plant will flower no matter how long each day’s light stretches. Even if it’s exposed, artificially of course, to continuous light!

Christmas cactusAbove 60°F, temperature steps in to play a role. At room temperatures, or thereabouts, a Christmas cactus needs about the same day length as does poinsettia, except that it might not need the weeks and weeks of short days before it decides to bloom. Then again, it might wait a few weeks, to throw in another wrinkle, depending on the variety of Christmas cactus.

My tack has been to give my plant reasonably good growing conditions, with bright light in winter and a little shade in summer and a well-drained potting mix rich in peat or other organic material,  and let it blossom according to its whim. In which case “holiday cactus” might be a better name for these plants than “Christmas cactus” because blossoms might unfold during Thanksgiving, Christmas, Easter, or anytime in between.

“Butterflies” in Winter

The last plant of this triad is my favorite: cyclamen. In bloom, it looks like delicate, red (or pink or white) butterflies fluttering above the mottled green, heart-shaped leaves.

Cyclamen’s native habitat — the Mediterranean, with its cool, wet winters and hot, dry summers — offers hints of the plant’s ongoing care and flowering needs. Potted cyclamen plantThis time of year, late fall going into winter, is when the plant is flowering and wants to be kept cool (preferably no higher than about 65°F.), moist (but not waterlogged), and in indirect light (which casts no more than a fuzzy shadow). Under these conditions, those butterflies can hover over the plant for weeks and weeks.

As spring comes — that is, “spring” indoors — leaves start to yellow and flowers fade. The plant is going dormant. At this point, the plant needs less water, the amount commensurate with the vibrancy of its leaves. Come fall, leafstalks start to appear again atop the bulb (botanically a corm, which is a short, swollen underground plant stem that is a storage organ), and the cycle begins again.

My favorite cyclamen species is Cyclamen hederifolium (ivy-leaved cyclamen).Hardy cyclamen in pot

Cyclamen flower in a crannied wall

Cyclamen flower in a crannied wall

It’s a very much scaled down version of the potted cyclamen you see for sale this time of year. It’s cute. Besides that, it’s also cold-hardy outdoors here. Some self-seeded “volunteers” even have established themselves to brighten up cracks between the flagstones of my terrace, blossoming each year in early fall.

Nothing To Do

If the garden, indoors and out, has no need of my attention at any time of year, it is now. I probably shouldn’t even be writing anything about gardening because pretty much nothing is going on. So I’ll make this brief.
Lack of light, warmth, and/or enough cool temperatures are keeping plants quiescent or dormant. The bonsai weeping fig, the Maid of Orleans jasmine (Jasminum sambac), the rose geranium, and other

Bonsai weeping fig, biding its time, for now

houseplants aren’t waiting for warmth. They’re indoors. These tropical plants never experience true dormancy; they’re quiescent, just sitting and waiting for better growing conditions, in this case more light.

My amaryllis bulbs aren’t waiting for brighter days. They’re now leafless, so can’t see the light anyway. Like the above houseplants, the amaryllis bulbs are now also quiescent, in this case from lack of warmth. Yes, it’s warm in my home, but not in the basement where the potted bulbs have been residing. I’ve brought the first pot of amaryllises upstairs where warmth — and water, the lack of which also has kept the bulbs purposely quiescent — can prod the bulb awake.
What about lack of enough cool temperatures to kickstart plants? That’s the case, now, with trees and shrubs outside. These plants are dormant, held back not by lack of warmth or water but by their internal physiology that needs to be switched before they’ll respond to good growing conditions.
No petals will unfold nor buds expand into young shoots until these plants are convinced that winter is over. That recognition comes after the plant experiences a period of cool — not frigid, temperatures — in the range of about 30° to 45°F. Winter’s “over” for these plants after about 1,000 total hours of exposure to cool temperatures, although the amount can vary among kinds of plants, even varieties of the same kind of plant. Also, a spell of midwinter warm weather can have the effect of removing hours from the “chilling bank.”
So what’s a gardener to do now? Nothing.
Okay, not everything green is just biding its time. Some tropical flowers take the opportunity to blossom this time of year, even if the plants might be otherwise quiescent.  Hence, we have holiday poinsettias and Christmas cactii sporting their red, pink, or white blossoms.
Not that poinsettia and Christmas cactus flowers will blossom willy nilly. As with trees and shrubs outdoors, these tropical flowers can be prodded to blossom with certain environmental conditions. They don’t know from cold, except that it damages them, so what they need to flower is a change in photoperiod. For late December blossoming, poinsettia needs 6 weeks of 15-hour-long nights uninterrupted by any light at all. Even a table lamp or a flashlight.
Christmas cactus behaves similarly, with an additional wrinkle. If temperatures are cool, in the 50’s, daylength (or, more properly, nightlength, because it’s the length of dark period to which the plants are responding) is immaterial. Plants will flower. If temperatures are warm, in the 70’s, daylength is similarly immaterial. Plants will NOT flower. With temperatures in the 60’s, plants will flower only after a period of 11-hour-long nights.
After a number of years of annual bloom, my poinsettia died, last summer. I got rid of my Christmas cactus many years ago to prevent its infestation of scale insects from spreading to other houseplants. I’ll eventually replace both but for now, there’s still nothing for me to do, gardenwise.
One plant that responds to some environmental condition, but I’m not sure what, is my orchid, the botanical mouthful Odontoglossum pulchellum. Every winter, sometime between the end of December and

February, my potted plant sends up thin flower stalks along which sprout white flowers whose thick petals look as if they were carved from wax and from which drifts a delicate fragrance. Blooms persist relentlessly, for weeks. The plants only flower in winter, but I’m not sure what exactly brings on the flowering.

After petals finally fall, the plants can take a rest, so need very little watering. The same goes for poinsettia and Christmas cactus plants. By then, of course, it’s late winter so seeds need to be sown and seedlings transplanted indoors, trees and shrubs need pruning, and there’s plenty of other stuff to do, gardenwise.