OrchidSafari ARCHIVES*
Pre-Discussion Material
GROWER'S TIPS
Marilyn H.S. Light
© 1997
Excerpted from
"Growing Orchids in the Caribbean" - © M. Light 1995, Macmillan
I learned how to grow orchids from those with a wealth of experience. I read, questioned, listened, observed and experimented with the techniques I had learned. There are so many different kinds of orchids and growing situations that it is virtually impossible to grow all of the orchids well using one simple technique. I discovered that the secret to good orchid growing lies first with choosing plants best suited to one's growing environment and that the only way to understand the growing environment is to measure conditions and keep records about seasonal changes. The orchid grower must be quick to observe when a plant fails to thrive and be willing to experiment with a different approach.
To successfully raise orchid plants we must understand their cultural requirements. We should also know how to modify the growing environment to meet their needs. A growing area can be designed with both the plant needs and personal goals in mind. If you wish to have flowers for year-round enjoyment, you must not only consider what kinds of orchids can thrive in your situation but also their blooming cycles. When choosing the kinds of orchids to grow, consider seasonal fluctuation of day and night temperature, of water quality, of air circulation, of shade and variations in shade over time. Measure and monitor temperature, light and humidity: keep records. This way you can perhaps discover why an orchid fails to thrive in one location yet is successful in another spot. Pay particular attention to the day/night temperature differential in your growing area as this is one of the most important factors in successfully growing and blooming orchids.
Occasionally a plant is inherently weak but more often unthriftiness is caused by inappropriate light, temperature or humidity. A pest or disease problem may be temporarily eased with application of appropriate pesticides but will recur if the cultural problem is not dealt with. A simple adjustment of shading or location is sometimes all that is needed to make an orchid thrive and be more resistant to pests and disease. Understanding orchids and how they grow is the ultimate challenge to the grower. Knowing when to be vigilant and how to modify the growing environment to meet orchid growth and blooming requirements will open the gateway to success.
Some thoughts on water, temperature and light.
WATER
Water is used to irrigate, mist, cool, and to apply soluble products such as fertilizers and pesticides. Small quantities of water applied at intervals during the day can cool the plants. Heavier applications are used to provide water and/or fertilizer. Time the last water application such that the leaves dry before nightfall. Withhold water during dull weather or if diseases develop in the collection.
Rainwater is the cheapest source of potentially good quality water. While rainwater is naturally acid due to the presence of dissolved carbon dioxide, it can become even more acidic from industrial pollution and combustion engine exhaust and contain substances which may be potentially harmful to orchids. Rainwater quality will vary greatly according to where it is being collected. If quality is good then the next problem is how to store adequate quantities for use during winter or during summer drought.
Estimate the quantity of water normally used during watering to calculate the quantity to be stored. Plan to store a minimum of 7500 liters (1500 gallons), much more for large collections. Construct a reservoir from concrete blocks or a poured concrete form, lining it with a rubber pool liner. A series of drums can also be used as a reservoir. Hide unsightly drums under benches. Use plastic drums or those lined with a substance that will not leach harmful minerals and other noxious substances into the stored water. Cover reservoirs to limit evaporation and algal growth.
Ground or reservoir water may be suitable for watering orchids but it often contains dissolved minerals that are damaging to the plants. There may not be a problem with occasional use of hard water containing dissolved calcium and magnesium but water high in sodium should be avoided. Water produced from sodium-exchange water softeners should also not be used with orchids. Estimate the mineral content of water with a conductivity meter such as the pocket-sized Salt Pen®. The lower the reading in µSiemens, the potentially better the water quality is for orchids.
Now that dispensers of de-ionized water are to be found in major supermarkets and drugstores, this product may be used alone or in combination with other water. One possible use is to use the more expensive product to flush growing media on a monthly basis.
EVAPORATIVE COOLING
Evaporative cooling works on the principle that as water evaporates from a surface, energy and heat are dissipated and the surface cools. One essential requirement is that the surrounding air is not already saturated with moisture. Water can only evaporate into unsaturated air. The lowest temperature that can be reached is the DEWPOINT at a given Relative Humidity. Orchids can be cooled directly by misting them with water. Using a fan to blow drier air over the leaves enhances the cooling effect. Blowing a strong air current through a mat that is continually being moistened with water will produce a similar effect. The speed of cooling depends upon the air flow. The following table gives the calculated maximum cooling that can be obtained at a given temperature and humidity.
EVAPORATIVE COOLING POTENTIAL UNDER VARIOUS HUMIDITY
AND TEMPERATURE SITUATIONS
© M. Light 1995 |
| % |
15° |
20° |
25° |
30° |
35° |
100% |
0 |
0 |
0 |
0 |
0 |
| 90% |
1.8 |
1.8 |
1.8 |
1.8 |
1.8 |
| 80% |
3.4 |
3.5 |
3.5 |
3.9 |
3.9 |
70% |
5.3 |
5.5 |
5.6 |
6.0 |
6.3 |
60% |
7.8 |
7.9 |
8.1 |
8.4 |
8.8 |
50% |
10.2 |
10.6 |
11.1 |
11.6 |
12.1 |
40% |
13.7 |
14.1 |
14.5 |
15.1
|
15.5 |
30% |
17.7 |
18.3 |
18.9 |
19.5
|
20.3 |
% = Relative Humidity ° = TEMPERATURE (°C)
LIGHT
Orchids need light to grow. Too much light can overheat leaves, slow growth and even kill sensitive plants. Less than ideal light for any particular orchid will result in poor flower production and susceptibility to disease.
Paphiopedilums and many other terrestrial orchids grow best with some shade but temperature, especially at the roots, may be more consequential to their overall vigor than the amount of light they receive. The best way to keep plant leaves cool is to provide shade and air movement. Pots should also be shaded or insulated from direct sun exposure. To determine the most appropriate light regime for a particular plant under your growing conditions, place that plant under 50 to 80 percent shade or in dappled sunlight for a time then move it into a brighter or shadier location according to how it behaves. If a plant requires more light, it will often bend towards a brighter light source. With too little light for their type, plants produce soft, floppy shoots and thinner leaves. Provide progressively more light to such orchids until their growth is stabilized.
Plants receiving too much light will react in a variety of ways including stunted growth and reddened foliage. Sometimes the orchid is reacting more to overheating than to the quantity of light. Improve air circulation and increase misting frequency to enhance evaporative cooling. Watch for signs that the orchid is responding to treatment such as renewed root and shoot growth.
PHOTOPERIOD
Blind sheaths on Cattleyas may result from inappropriate photoperiod. Photoperiod-sensitive plants have evolved such that the length of night or darkness interval triggers blooming in a particular season. Winter and spring-blooming orchids including many Cattleyas depend upon a series of uninterrupted long nights for several weeks or months to stimulate bud development. Any interruption of the induction process will arrest flower development. A street light, landscape lighting and artificial illumination of the growing area, even for a few minutes every night during the induction period is sufficient a disruption.
SUMMARY
I began growing orchids in the tropics where contrary to what temperate residents might believe, there are just as many challenges to orchid growing. The challenges may be different but the problem-solving methodology is the same.
I applied the same problem-solving techniques when I returned to Canada. Modern technology permitted me to sleep soundly while an inexpensive electronic recording device monitored the lowest temperature reached in my growing area during the night. Relative humidity was similarly monitored. A handy remote probe assisted me in monitoring both the temperature within a pot and that of the surrounding air. Using such devices to gather data allowed me to determine how to set up my winter under-lights growing area which is in a plastic tent in the basement. I discovered that for my mixed collection of warm-, intermediate- and cool-growing orchids, it was best not to use a fan. A fan mixed the air such that the average temperature was too high for the cool growers and too cool for the warm growers. Without a fan, a temperature gradient develops such that plants on the top shelf have 25°C max/18°C min, plants on the middle shelf have 20°C max/15°C min, and plants on the lower shelf have 16°C max/12°C min. Thus I can grow Masdevallia livingstoneana and Phalaenopsis warm and Masd. decumana and Sarcochilus cool. To avoid stagnant humid air and possible disease resulting from poor air circulation, I do five things. 1) plants are misted and/or watered only in the morning to allow sufficient time for foliage to dry before night. Relative humidity hovers around 40% - 60%. 2) Fertilizer application is very dilute and less frequent than in summer when the plants receive 16 versus 12 hours illumination. 3) Any new acquisitions are kept in a separate growing area for about 3 months to avoid the introduction of disease. 4) The collection is observed regularly for any sign of malaise. 5) The tent does not extend right to the concrete floor thus permitting natural convection currents to develop.
This situation works for me under my growing conditions. I do not advocate that anyone else raise orchids without mechanically-assisted air movement.
Measure, record, monitor, experiment and share your experience with others.
These are my Grower's Tips that I willingly share with you. Good Growing!!
