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.

Pruning workshop

Propagation Mania

And the winner of my book giveaway from last week is  . . . (drum roll) . . . reader Meg Webb. Hey Megg, send me an email with your mailing information and I'll get the book to you. Thanks to everyone else for their feedback.

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I have to admit a certain addiction for propagating plants. You would think that, what with sowing cabbage and Brussels sprouts seeds for transplants last week, starting tomato transplants in early April, grafting to make new Korean mountainash and apple trees and . . . ., any appreciation for propagation would be fulfilled.

But no. The seeds within a freshly eaten kumquat; why not plant them? Some of the seeds within a just eaten hardy passionfruit (Passiflora incarnata); plant them also. Not that every seed gets planted. Just some of the more unusual ones or just a few of those that are more usual. Without any restraints, a forest of apple and pear trees would have long ago inundated me.

My mania came to the fore again yesterday as I was neatening up some houseplants. The rose geranium had grown very leggy, with three or four lanky shoots, almost leafless except near their ends,

stretched out to a very unattractive 2 foot length. All that was needed to bring the plant back to its visual glory was to cut everything back to some tufts of leaves sprouting near its base. Which I did.

But those pruned stems; could I really just toss them into the compost pile? No. “Make new plants,” whispered the devil on my left shoulder. Which I did.

All that was needed to make more of this relatively easy-to-propagate plant was to cut the pruned stems into 4 inch lengths, with each bottom cut just below a node and each top cut just above a node. Best wound healing is at nodes, so such cuts avoid dead stubs with poor healing.

All but 2 or 3 leaves were removed from the 4 inch stem segments at the ends of the stems in order to strike a balance between cutting down water loss from the as yet unrooted stem pieces and allowing for some photosynthesis to feed the stem. To grow new leaves and roots, the leafless stems segments will have to rely on their stored energy reserves. To save space, I filled a flowerpot with potting soil and poked each stem segment about two-thirds of its length deep into the soil, then watered.

A clear plastic cover over the planted pot increases humidity to further reduce transpiration of water from leaves until roots form.

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Pruning shrubs, which generates a lot of stems, could be a real test of my restraint.

Shrubs are shrubs because they generally don’t have long-lived permanent trunks, like trees. Every year, new stems arise from at or near ground level. The way to prune shrubs, then, is to capitalize on this characteristic, by so-called renewal pruning, each year removing some oldest stems and excess youngest stems (suckers). Pruning is done near or at ground level. In so doing, the roots get older and older but no stem ever gets very old, and youngest stems have room to develop.

Easy enough. The wrinkle in renewal pruning is knowing when a stem has overstayed its welcome. If you know the plant, you can just look up the information -- in my book, THE PRUNING BOOK, for instance, in which I group all shrubs into one of four pruning categories.

Easiest of all is to prune is the category of shrubs that includes witch hazel and tree peony. These shrubs perform well on old stems and make few suckers so no annual pruning is necessary to keep them looking prim and proper.

Lilac and forsythia are in the category of shrubs that flower on one-year-old stems originating up in the plant off older stems. So individual stems need not be cut back until they are a few years old. Each year, though, many new sprouts originate at ground level, too many. Their numbers need to be reduced enough so that those that remain have sufficient elbow room as they age to replace older stems that will be cut away.

Kerria is in the category of shrubs, along with snowberry, abelia, and rambling roses, that blossom best on one-year-old wood growing up right from ground level. Prune them by cutting away all stems 2 years old (and older, if a shrub has not been or is not being pruned annually).

The final category, counting butterfly bush and Hills-of-Snow hydrangea among its members, perform best on each season’s new, growing shoots. They’re also very easy to prune: Just cut the whole shrub down in spring. That’s a lot of stems for propagating. Still, restraint is easy with butterfly bush because the stems anyway are typically dead here by the end of winter. The roots survive, though, giving rise each spring to shoots that flower in summer.

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Pruning one of my filbert bushes

My filberts present one more wrinkle in shrub pruning. Filbert can be trained as a tree or as a shrub. But consider: filberts are susceptible to a disease, filbert blight, which can eventually kill a stem. This makes a good case for renewal pruning, i.e. growing them as shrubs. On the other hand, squirrels love filbert nuts, and one way to keep them at bay is with metal squirrel guards, feasible only on filberts trained as trees.

For now, dogs, cats, traps, and high grass have kept squirrels at bay, so I’m opting for filbert shrubs. The stems are very difficult to root so today’s prunings don’t even tempt me.