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Treating Cold Damaged Orchids

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Cold damage appears on orchids as whitening of the foliage and stems. The white gradually turns to brown as the effected tissue dies. Often this dead tissue simply dries and the damage is limited to the unsightly patches that are left. Frequently, however, the damaged tissue is infected with bacterial rot which can spread in the plant and cause further damage. 
Softening of the edges of the cold damaged areas or oozing of brown fluid indicates bacterial infection. Removal of the leaf or stem is a simple but somewhat drastic solution. If one is loath to lose so much of the plant, the most effective treatment for bacterial infection is treatment with cupric hydroxide (Kocide or Champion) which should if possible be combined in equal parts with mancozeb (Manzate or Dithane M45). 
This combination is packaged, pre-mixed as Junction. By adding a small amount of water to the chemicals in a jam, one can make a slurry that can be brushed on the lesions.

Be cautious when making the slurry not to inhale any of the dust and never, never, dust these chemicals without wearing a mask.

An old toothbrush is efficient in applying this and your dentist will be happy to have it out of your mouth. Any left over slurry can be placed on a high shelf (brush and all) and re-hydrated later. This stuff is also the cure for those soft spots that appear on Phal. leaves in summer. 
For large collections, with extensive damage, one tablespoon per gallon of cupric hydroxide and mancozeb can be sprayed. Mix the two and wait an hour or more before spraying. Do not apply this mixture to dendrobiums which are hyper-sensitive to copper or to bromeliads (ditto).

Cold Temperature Tolerance of Different Orchids

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One major obstacle for neophyte growers is in understanding the diversity of cultural requirements of various genera of orchids. Orchids are such a vast group of plants which have succeeded in nearly every conceivable habitat on earth, that knowledge of a specific genus’s cultural requirements, rather than a general knowledge of what “orchids” like, is necessary to successfully cultivate the various types. Most cultivated orchids come from tropical regions but differences in elevation and other geographic features of their native habits can mean dramatic differences in the response of orchids to various external conditions. Most emphatically these differences can be seen in different genera’s toleration of cold. While some orchids are native to regions where frost is more the norm than the exception, others are hyper-tropical plants for whom 50 F (10C) is far too cool. Knowing which is which is essential in a mixed collection of orchids. A great irony for beginners is to discover that their extra nurturing efforts to protect certain orchids have in fact done more harm than good.

            Dendrobiums are among the most confusing for new orchid growers. This huge genus, well over a thousand species divided into 15 sections, ranges over nearly a quarter of the planet. Found from western Indian all the way to Micronesia, dendrobiums inhabit an incredible variety of ecological niches. Ironically, the two sections most common in horticulture are diametrically opposite in cold tolerance. Section  Dendrobium, the soft bulb or “nobile types” whether in their pendulous forms like Danosum and aphyllum or in the upright types like D. nobile and its hybrids, positively relish the cold. Temperatures right down to frost are the best culture to produce the most prolific blooming of these plants. Without cold and drought stress in winter these plants will retain their leaves and produce an abundance of vegetative growths but few if any flowers. Stressed by cold and dried out properly these plants lose all their leaves and in spring the bare bulbs are covered in flowers. The opposite is true for the “hard cane” dendrobiums of sections Spathulata and Phalaenanthe. Loss of leaf on D. phalaenopsis types is usually indicative that they have suffered from too much cold. Temperatures below 60F (15C) can produce this undesirable effect. D. phalaenopsis and evergreen types should receive the maximum cold protection.

 Other sections of the genus have slightly different tolerances. Section Callista, D. farmerii, D. lindleyii (aggregatum) and their relatives can take temperatures nearly as low as the nobile types and will bloom all the better for exposure to temperatures in the 30's (3-5C). Section Formosae, D. formosum, D. infundibulum and the new hybrids prefer slightly warmer conditions but are quite happy with temperatures in the 40's (6-9C).  Other sections of Dendrobium in cultivation such as Pedilonium, Latouria, and the Australian hybrids of section Dendrocorne have slightly different requirements and those growing these more “exotic’ will succeed best in researching them. Try B. Lavarack et al. Dendrobium and its Relatives, Timber Press.

            After the cold sensitive “hard cane” dendrobiums, Phalaenopsis are the most tender of commonly grown orchids. Phalaenopsis will be strongly induced to bloom by temperatures in the mid 50's (12-13C). A few exposures to temperatures below 60F (15C) will produce the desired spikes and thereafter the plants will be happiest if they are kept above 60. One or two nights down to 50 or slightly below will do little harm but are to be avoided in the best kept collection.

            Vandas come next on the scale of sensitivity. Like Phalaenopsis they are stimulated to bloom with sharp drops of temperature into the 50s at night, especially when the temperature can be induced to climb into the 80's (27-32C) by day. Vandas will tolerate brief excursions into the upper 40's but are best keep above 50 degrees. Temperatures below 50 for very long or very often will produce the tinkling sound of falling Vanda leaves, turning the plants into palm trees. 52.

            Oncidiums of the “mule ear” type with thick fleshy leaves (O. luridum, lanceanum etc.) have warmth requirements similar to vandas. The thinner leaved Oncidinae will usually take temperatures into the 40's with aplomb. Many of the hybrids in this group have been bred to Miltoniopsis and to Odontoglossum to increase their cold tolerance. A caution with this group is the ability of wind to strip heat rapidly from their thin leaves. The cold tolerance of these will be much greater in still air.

            With the exception of some species of Amazonian origin like Cattleya violacea, most cattleyas can take quite cool temperatures. Most growers have few concerns for them even in temperatures down to the upper 40's (8-9C). They must, however be protected from both frost and freeze. Be extra cautious on those clear still nights when the temperature drops to the 30's (3-4C).

            In addition to the cold loving nobile dendrobiums, certain other genera from the high Himalayas such as deciduous Calanthe and Cymbidium species and hybrids, actual require quite cold temperatures to stimulate them to their best bloom. Even “warm growing, temperature tolerant” hybrid cymbidiums flower best when chilled repeatedly into the low 30's.

            All orchids tolerate cold best when they have proper nutrition. Avoid too much nitrogen which might stimulate too soft of growth and increase the dosage and frequency of application of both magnesium and potassium in colder weather.

Treasures from the Storm

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Excerpted from Florida Orchid Growing: Month by Month page 126-127 by Martin Motes. All rights reserved.

It's an ill wind that blows no one any good. Minor hurricanes are still a major nuisance but small blessing can nonetheless flow to South Florida orchidists in the enforced pruning of our trees which will bring cherished light to our orchids. The prunings themselves are a major resource for the clever orchidists. The streets of South Florida are typically lined with a virtually inexhaustible lode of great orchid mounting material in the wake of minor hurricanes. All that is needed is the energy to cut and haul the appropriate branches that will supply years of great orchid mounts. With such an abundant (dare I say windfall?) one can even be quite picky. The savant orchidist should select his material with an eye to the best suited and the most appealing. Three species stand out. First, the golden trumpet (Tabebuia argentea or caribae) whose cork like bark is ideal for most orchid genera is always the first to fall and particularly abundant in roadside plantings. 

Live oak (Quercus virginiana),a favorite host of our native epiphytes, is also highly favored by epiphytic orchids in general and dendrobiums in particular. It is, of course, of the very same genus as cork itself and the wood is highly durable. 

 Next among the commonly fallen and desirable is button wood (Conocarpus erecta) both green and silver, again a favored host of native epiphytes. These branches is "driftwood" on the hoof. It is the roots of this species that become the "driftwood" of orchid culture. The branches are great mounts too.

Other species such as bottle brush (Callistemon) are good but the three common storm victims will provide more than enough of the very best mounts. Look for branches that are forked or twisted or that have other distinctive turns that will add character to the finished mounts. 

 Try to imagine the plant situated on the branch. A small chain saw makes short work of these branches, quickly rendering them into raw works of art. A well sharpened double set hand pruning saw will do fine. Now would be a good time to acquire these tools if needed before they are inevitable truly needed in the aftermath of a major hurricane. When a "minor" storm has passed, we can count our blessings and collect the orchid manna falling from heaven.

Hurricane Orchid Prep

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With Irma threatening, we are republishing our advice for hurricane prep.

When a hurricane is looming one should run all the orchids as dry as possible to reduce the threat of fungus and bacteria. But contra-intuitively, just before the storm strikes one should saturate the orchids to the max. Now is the time to do that [Note: this piece was originally published the day before Matthew hit, so, water heavily the day before the hurricane makes landfall]. First, because we want the plants to be as heavy as possible to help prevent them being blown away or about. Second, because if one's water source is a well, electricity for the pump may be off for days or even weeks. Thoroughly watered plants will be much happier should this occur. Even if you are able to bring all your collection inside, water them thoroughly with two to three applications spaced a few minutes apart. They will be perfectly happy for a day or two without water and we will all have enough mess to deal with without watering orchids in the house.

Remember, wind velocity increases exponentially as height increases. Get your plants as close to the ground as possible but off the ground as flooding may saturate them with fungus and bacteria. Usually it is not wise to attempt to cover them with a tarp or shade cloth as the whipping of the cloth by the wind likely will cause more harm than the wind itself.

If you are growing under shade cloth, the cloth should be furled tightly to protect it. Bright burning sun is typical in the wake of a hurricane and shade will be invaluable If you are growing under trees be prepared for the possibility that the protective canopy will be destroyed. Have a plan to protect your plants from sun burn.

Good luck and please feel free to share this information with whomever may benefit from it.