Of Orchids and Oil

Over the past few weeks, excitement was steadily mounting on the windowsill. First came the stalk that poked up from the bases of whorls of leathery leaves. Then, buds started fattening up along the stalks. Finally, after a half a decade of growing Dendrobium kingianum, the pink rock orchid, it looked like the plant might finally reward me with some blossoms. Which it did, a couple of days ago.

The actual blossoming was somewhat anticlimactic. No flamboyant shapes or colors, just small, white blossoms. And no particularly green thumb was required to get this orchid to blossom, just time.

Pink rock orchid is known to be a tough plant. While many orchids are native to lush, tropical jungles, the conditions of which are hard to  even approach, indoors except in a hothouse, this orchid is native to rocky environments of Australia. It tolerates cold below freezing and hot temperatures over 100°F., and does not demand an inordinate amount of light. I water whenever the potting mix seems dry.

The problem is that “orchid flowering” conjures up both a greater challenge and blossoms more spectacular than are offered by pink rock orchid. So I’m now just going to look upon it as an attractive houseplant with an attractive flower. It even has a pleasant, slight scent.

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I’ve waxed enthusiastic about the handfuls of ripe figs I gather up in late summer and into fall from my greenhouse. And about heads of lettuce and mâche, celery stalks, and sprigs of parsley that fill salad bowls all winter. Yet all is not always so Eden-like within the greenhouse. Last year scale insects began to attack a couple of fig trees. Innocuous-looking, small bumps on the bark -- dormant scale insects -- threaten to wake up in a larger outbreak this year. Action is needed. Now.

Last year at this time my weapon was an old toothbrush and a solution of soapy water. The brute force method of scrubbing the insects from the bark was effective -- to a point -- but tedious.

This year I’m smothering the buggers. My weapon of choice is oil, not any old oil but a specially refined oil that minimizes damage to plants while leaving insects gasping for air. It also contains an emulsifier so it readily mixes with water. Spray oil comes in two “flavors:” dormant oil and summer oil. Plants are more likely to be damaged by oil when they are in leaf and growing, so summer oils are more refined; summer oils mixed at higher concentrations can be used as dormant oils. (Summer oils are also called “horticultural oils,” “stylet oils,” or “ultrafine oils.”)

Oil sprays have been around for a long time -- commercially for over a hundred years -- and have the advantages of causing little harm to beneficial organisms and being relatively safe for birds, humans, and other mammals. Insects and mites (which oils also control) have little likelihood of developing resistance to oil sprays. The oils might be petroleum-, plant-, or fish-based.

So what’s not to like about oil sprays? Most importantly, they can damage plants. To avoid damage, sprays must be applied when temperatures are above freezing but not too, too hot, say above 90°F. Also, some plants, such as Japanese maple, redbud, azalea, hibiscus, and sugar maple, are readily damaged by oil; and oil will strip the blue, waxy coating from Colorado blue spruce, turning the needles green. The longer any plant is coated with oil, the more chance for damage; low humidity hastens its evaporation.  

Spray oils work by direct contact, which is advantageous unless you have a pest whose eggs are resistant to oil and keep hatching over time. Or if the pest flies in from elsewhere. Many gardeners routinely spray their fruit trees in spring with oil, with little effect because the most significant pests of fruit trees generally do not hang out on the stems or fruits for long enough for a direct hit by an oil spray.

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Back to the fig trees in my greenhouse. They’re getting weekly sprays of dormant strength summer oil until the leaves begin to unfold. Once that happens, I may mix up a batch of summer strength oil. The goal is to reduce populations drastically because, despite the innocuousness of oil sprays, I’d rather not spray anything once fruits begin to develop.

My other tack to keep scale insects at bay is to wrap the trunk with a band of masking tape coated with sticky Tangletrap, providing a Maginot line to stop ants from climbing the trees. (Hopefully, more effective than the real Maginot line.) Ants enjoy the sweet honeydew exuded by the scale insects and, in return, herd them, protecting them from predators.

Spraying and banding may seem like a lot of effort. But fresh figs are worth it. And with snow still on the ground, there’s not that much else to do, gardenwise, yet this time of year.

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.

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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.

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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.