- Average high: 76.5
- Average low: 59.6
- Average mean: 68.1
- Average rainfall: 1.88"
January is somewhat like December but in reverse, with each succeeding day bringing longer hours of sunlight until days are long enough that afternoons return at the end of the month bringing extra sunshine to warm us after the extra sharp cold snaps. January, like December, is cold and dry, in fact even colder and drier. Dry is good, cold can be very bad. We need to accentuate the positive by especially careful watering in January. By keeping our plants as dry as possible and spacing our waterings as far apart as possible, we conserve our potential to use water to protect our plants from the cold, keeping our powder dry, as it were. In January water early, water thoroughly when you do and do so sparingly. The cooler overall temperatures of January are much less dehydrating even to plants which have received less water. remember, many of our orchids come from seasonally dry and cool climates not so different from South Florida. Many orchids are equipped to handle the drier cooler conditions of our January. A good strategy is to “top-up” the light watering that our plants receive with the passing showers that each successive cold front brings. This slight additional irrigation may prove to be all the watering that many genera need. Such parsimony, preserves the possibility of using water on truly cold nights to warm our plants.
Water is the only feasible source of heat available to plants grown in the open, under trees, in shade houses or on patios in South Florida. Ground water here (and in most of the rest of the world is about 63 F. (16C). Water out of municipal systems is not far different. On truly cold nights turning on the water can be of great benefit to our plants, provided that they have not been over-watered in the days and weeks preceding, thus inviting the ever present fungi to do more damage than the cold. For this reason as well, in general, orchids are better off dry until temperatures approach frost or freezing. The logic for maintaining plants dry is not only to minimize fungal problems but also because cold air is typically very dry air. If plants are wet in very dry and rapidly moving air say 10 or more MPH, evaporative cooling can take place, chilling our orchids further and faster than they would if dry. When the water goes on it needs to be in heavy volume and it needs to stay on to keep the plants thoroughly bathed in its warmth. Very still air on the other hand, presents a different danger as frost is possible at temperatures higher than is commonly realized. In calm air frost can form at higher elevations and settle in on plants while the surface temperature is only in the upper 30's. The best forecast for nights when the temperature will hover near 40 is a light wind of 2-5 miles per hour. This light wind mixes the warm air near the surface and draws warm from the earth. Clear, cloudless, still nights with bright shining stars elevate the spirit but harbingers frost.
Forecasts of temperatures below 40 F should stimulate us to action.
If it is not practical to bring all the Phalaenopsis, vandas and hard cane dendrobiums into the house or garage, think of using water to help protect them. Shade cloth or even patio screen hold in a surprising amount of heat like an lacy Mantilla. Under screen, a fine mist head attached to a hose and left running beneath the bench or plant rack will provide several degrees of additional warmth that will often sufficiently temper the chill and ward of any light frost settling in. Growers with swimming pools frequently turn on the recirculating pump to keep a supply of warm water near the pool’s surface where it can add heat to the ambient environment. A few degrees of warmth frequently makes all the difference to our sensitive orchids. In more open areas not protected by a permanent irrigation system, an oscillating sprinkler at the end of a garden hose is very effective. These are readily available at Home Depot and garden shops for a few dollars. On frosty nights, start the water at bedtime and let it run until the sun is up. The extra water once or twice in a month will do no harm to orchids that have been properly and judiciously watered the remainder of the month. In fact, these occasions present the opportunity to be sure that excess fertilizer salts have been leached from the pots and medium. A good work can be born of necessity!
Remember that Himalayan dendrobiums and ‘‘warm growing’’ Cymbidium hybrids will positively relish temperatures down to 32F and a light frost is just the ticket for great bloom. Keep the water off these!
In the drought of January, mites, which affect nearly all genera of orchids, continue to be a serious problem that will only get worse. They will reach a crescendo in March and April but January is a good time to scotch them. Paphiopedilum and other softy leaved genera are particularly susceptible but no genus is free of them. One theory on why deciduous genera such as Catasetum, Calanthe and others lose their leaves hypothesizes that this totally rids them of mites.
Being totally rid of mites is a good thing! Sometimes this is easier said than done because mites reproduce with such voluminous speed. Their life cycle from egg to reproductive adult being is as short as twelve days. In order to control mites one must achieve as total a kill of the population as possible. Total control can only be achieved with two successive sprays. After spraying for mites initially, one must spray again in 7 — 10 days. No single spray is totally effective in killing both adults and eggs and a second spraying is necessary to kill any survivors before they can reproduce. Oil as recommended in the December chapter at 1.5 oz per gal followed in7-10 days by soap at the rate of 2 oz per gallon is very effective. These treatments are also quite effective against scale and mealy bugs which thrive on drought as well. Be sure your plants are well watered the day before applying both oil and soap and be sure that you cover thoroughly all leaf surfaces especially the lower ones which are mites favorite hide outs.
For those who wish to be more aggressive, the University of Florida IFAS recommended chemicals for mite control are:
Avid 0.15 EC
Always follow label instructions for use. Any of the can be alternated with the soap or the oil in the 7-10 day cycle.
Controlling mites pays huge dividends! You’ll be surprised at the extra vigor your plants display.
As cold is a major theme of this month, a review of some factors effecting temperatures in South Florida should be particularly valuable to new comers in the wide world of orchid growing.
While we bask in the warm glow of a tourist board’s vision of winter, (made all the warmer by thoughts of our envious friends and relatives stuck in the northern snow and ice) we should be mindful that January can produce quite severe cold. The majority of hard freezes in Florida take place in January, and even short of that catastrophe, the month usually brings the coldest weather of the year. We need to keep a sharp eye on the weather reports while remembering that in our almost island of Florida a number of factors influence the severity of the cold which will impact us.
First the shape of the cold front interacting with the shape of the peninsula. The weather that delights the tourist board and all of us while plunging most of the US into the throes of ice and snow usually result from particularly large, slow-moving masses of cold air that have spread across much of the continent before reaching Florida. Large broad masses of cold air that seep downward over a broad front also cover the Gulf of Mexico and the Atlantic as they progress southward. These tempering bodies of water bathe the cold to merely refreshingly brisk temperatures. More dangerous to our plants are the smaller, tighter, fast-moving fronts which plunge like a dagger of cold straight down the peninsula to the tropical heart of South Florida. Such fronts typically spawn the freezes and severe plant-damaging cold that is of the greatest concern to orchidists and other plant people. These Siberian Express fronts bring winds out of the Northwest that are un-influenced by the benign, protective bodies of water flanking the peninsula as they drive down the central landmass of Florida. When the winds from an approaching front start out from the southwest and move gradually to the northwest and then quickly to the north and northeast, we can expect cold nights and warm days that reasonably well-protected orchids not only tolerate but in some case actually relish. The more savage fast moving fronts where winds start in the Northwest and stay there are the ones to send us thinking of moving plants or providing additional heat.
Wind direction is always critical in South Florida. Because of the peninsula’s decided eastward cant, winds from the north in much of South Florida are in fact relatively mild. North winds here are blowing across the warm Gulf Stream. The first shift to the northeast absolutely spells relief as the warm Atlantic has absorbed the cold.
Wind speed is also important. Strong winds at low temperatures chill our plants more rapidly, exposing them to additional hours of chilling. “Wind chill factor” has no relevance to plants until the actual air temperature drops to a level unacceptable to the plant. After that, the more rapidly the plant itself’s temperature falls to that damaging level and the longer it stays there the worse the case. Wind speed enters the equation only if the final low temperature is below our plants’ tolerance. Wind breaks of vegetation or manmade are always to be sought. Native epiphytic orchids hide out in the most protected hammocks and sloughs. We can learn from them.
Dead, still air looms with another threat: radiational cooling which can allow frost generated at higher levels of the atmosphere to settle in on our plants even when the air at the surface is only in the upper 30's. These frosts typically occur when the front has passed leaving such low humidity that there is no moisture in the air to retain ground heat which radiates quickly into the cold reaches of space. Light winds of 2-5 miles an hour are our friends on these nights. They stir additional heat from the ground and keep the colder upper air from settling in.
Relative humidity also has a profound effect on temperatures. Dry, clear air allows heat to radiate out into space. Those bright starry nights are beautiful but as Good King Wenceslas knew they are not necessarily our comforters. The best measure of the dryness of the air relative to cold is the dew point. When water vapor is wrung from the air an incredible amount of energy is released and the heat of transformation raises the air temperature a degree or two. Because of this phenomenon, the dew point is usually the closest measure of the coldest temperature that will be reached in the night. Particularly on still clear nights it should be monitored closely.
Wind direction, wind speed, dew point — where does one find these on a chilly night? At the Florida Agricultural Weather Network (FAWN), a system of automated weather monitoring stations, as close as your computer. There will be a station near you. There are also several at points north of the nearest location that give data on conditions that are effecting areas through which the cold front is moving toward us. FAWN is updated every 15 minutes here. Bookmark it for something other than worrying to do on those cold nights