Temperatures between 10° to 27° C tend to be perfect for orchids, however on occasions the brief periods of temperatures above 138 C can drop even into the 0 C, and it will not harm most orchids as long as no frost forms on the leaves. Cold injury includes damage from temperatures above and below freezing. Chill injury is damage caused by low temperatures above freezing, and freeze injury is damage from temperatures at or below freezing. Frost damage takes place when dew freezes after it has condensed on leaf surfaces if the ambient temperature falls below freezing.
Plant Response to Cold Temperatures
Consider cold hardiness when adding new orchids for your landscape or collection. This is the measure of the orchid’s tollerance or ability to adjust to cold stress. The degree of cold hardiness is directly decided by environmental conditions and the plant’s genetic makeup. Colder temperatures always can kill Some species, while others can tolerate only short periods of temperatures near freezing.
Cold Injury Symptoms
Cold injury symptoms generally become visible, not during the cold snap, but some days after exposure to dangerously low temperatures. The rate at which symptoms develop depends upon the severity of the exposure and the conditions in the growing environment afterwards. Continued cool temperatures and high humidity after exposure to cold may slow the development of symptoms, while high light intensity and slightly hot temperatures may make symptom development happen faster.
Chilling
Many chilling-injury symptoms are happening often to other stresses such as lack of water, root-rot diseases, chemical phytotoxicity and heat and light stress; as such they may be hard to diagnose. General chilling injury symptoms are:
~ More susceptible fungi and bacteria attacks.
~ Accelerated rate of natural death.
~ Slowed growth, or limited growth blush. This may be difficult to notice without non-chilled plants for comparison or a detailed knowledge of the orchid’s normal growth rate.
~ Internal discoloration (browning).
~ Surface lesions, pitting, large, sunken areas and discoloration. Soeking the tissues in water is usually followed by the browning and wilting process.
Freezing
Desiccation or burning of foliage, water-soaked areas that progress to necrotic spots on leaves and death of sections of the plant or the entire plant are the symptoms of freeze injury . Clear symptoms may not be appeared till after the plant has been stressed by slightly hot temperatures.
Protecting Your Orchids from Cold
Orchids, even as landscape plants, can be pulled through a tough winter. The more trouble you take, the better your results are possibly to be.
Moving Plants Indoors: Container-grown outdoor plants can be moved to a slightly hot garage or other indoor particular place for cold protection. If this is not an option, decide in advance which plants are most important to you. It is not a bad plan to mark those with a colored label, or keep them all in a particular spot. That way you will not be searching through hundreds of plants and labels to find them, if you do need to gather them fastly.
Also notice, before winter arrives, which orchids in your collection dislike cold. Many generally grown orchids have to bear those cold temperatures ranging to 13° C during the night, amoung the orchids include the Stanhopeas,Miltonias, Oncidiums,Vandas, Lycastes, Odontoglossums, Masdevallias, some Cattleyas, Catasetums, Dendrobiums, and cool-growing Paphiopedilums. However you can say that most Cymbidiums can survive during the winter night temperatures in the 40’s (4° C), and many need such a stimulus to bloom well.
White or yellow Vandas, as well as some Dendrobiums (Phalaenopsis and antelope-type), are particularly easily affected and do not like temperature drops below 60° F (16° C); they can be particularly likely to losing leaves when exposed to cold temperatures. Cattleyas tend to be more hardy.
Seedlings and immature plants, especially those in flasks or compots, are generally much more easily affected to cold temperatures than their fully grown counterparts. Items to keep on hand to transport your orchids fast in an emergency include boxes, plastic flats or small crates and possibly a wagon or cart.
Please ready indoors to be used as a temporary area of growth for the arrival of the orchids. A spare room, garage, or even a spare bath will work at a pinch. perfect growing environments are not the primary consideration; this is just a few days’ shelter until the cold passes. The area can be layered on top with plastic tablecloths, sheeting or tarp to protect floors and finishes. Heat, lighting and ventilation should be sufficient; inexpensive supplementary heaters, lighting and a fan for air circulation can be purchased at local hardware suppliers as needed.
Protecting Plants Outdoors
Do not keep watering plants the day before a cold night, because the less moisture in the plant’s cells, the better it will bear a freeze.
If they are not cold sensitive, or temperatures will not drop too low, plants can be moved to the ground rather than indoors, or even covered and left in place. Occasionally, more damage can be caused by moving plants frequently than if they are kept standing still.
Have wraps, clothespins, plastic sheeting and twine ready in case of cold. insulating wraps can be many materials. Frost cloth, available at most hardware stores, is lightweight and traps heat, but also is designed to breathe. You also can use sheets, blankets, towels, hessian and other coverings. Covering wraps in plastic that is kept from touching the plant by supports will provide an extra measure of protection from wind. Avoid using plastic directly on the plants. When the sun and temperatures go up, plastic can trap too much heat and cook the plants. you can utilize it as a windbreak during the night and well vented during the day.
In addition to the insulating wraps and plastic covering, additional mulch at the base of bedding plants (reed-stem Epidendrums, Arandas, Mokaras, etc.) will help protect them from freezing temperatures. When the weather becomes warm, the additional mulch should be taken away.
Treatment of Plants After Cold Stress
The conditions to which plants are subjected after cold stress affects the level of injury and rate of symptom development. The importance of post-exposure environment differs with the severity of cold stress. Damage to plants exposed to extreme temperatures may be influenced by post-stress dealing.
Intense light, low humidity and high temperatures following chilling of some tropical plants causes increased water loss through transpiration. If the chill exposure has damaged water absorption, temporarily or permanently, Extreme water stress can develop.
Cold injury to roots may not be obvious till spring, when plants are stressed by higher temperatures. Unsuccess to start a spring growth flush may be the only visual symptom of winter injury, and little can be done to minimize its effects by this time. Weakened or injured plants are more susceptible to disease attack, so growers should keep an eye out for symptoms and possibly use a preventive fungicide. Increased shade may also lessen heat or water stress during the recovery period.
After the Fact
If the worst occurs and your orchids are destroyed by the cold, do not assume that they are dead. Allow the medium to dry, and keep the plants in a humid condition out of direct sun and high temperatures. Do not water till new growth start to grow, producing shoots, buds, or leaves. Watering may be resumed at this time, first with simple water, followed by a light dose of a fertilizer with a full compliment of minor elements when new roots develop.
The positive part of the occasional winter chill is that, in many cases, cool periods help induce or improve bud starting and flowering.