Pakkret Floriculture

The process from flower bud induction in the new growth to blooming can be divided into three stages.

Stage I : Flower Bud Initiation in the New Growth

Stage II : Flower Spike Initiation

Stage III : Spike Elongation and Blooming

Stage I : Flower bud initiation in the new growth (This stage does not require the temperature as low as Stage II and III)

Normally, flowers of a cymbidium are initiated within the new growing pseudobulb. If the plant grows in suitable conditions, where night temperatures are below the plant’s required maximum night temperature, their pseudobulbs will be bigger and healthier with larger and thicker leaves. Commonly, lower temperature at night reduces plant respiration; therefore plants expend less stored energy. As a result, more energy is accumulated in their storage organs. Eventually, those pseudobulbs have a higher potential to produce better quality flowers with a higher flower count.

If the required night temperatures are not met, pseudobulbs will tend to produce poorer quality flowers and a lower flower count per stem. In the worst scenario, they may not produce any blooms at all. This means that no matter how you treat those pseudobulbs, they will not produce any flowers, even though they may later experience a cooler growing environment. Literally, those pseudobulbs are wasted.

It is a general rule that the large-flowered types need greater energy storage in their pseudobulbs than the smaller-flowered types do. In other words, the large-flowered types require lower night temperatures than the smaller-flowered types do.

Traditionally, all the commercial large-flowered cymbidiums have been developed from large-flowered species that originally came from the foothills of Himalayan Mountains, starting from northern India, Nepal, Bhutan, northern Burma, and southwestern China and throughout many smaller ranges in Vietnam, Laos and northern Thailand. In these original habitats, their climate is divided into wet and dry cycles.

1.The wet season is the monsoon season of Asia. During this season, these areas experience ample rains with higher daytime temperatures. However, their nighttime temperatures drop drastically by 10 to 15 degrees and become cool. This is a common climatic occurrence at higher elevations. The monsoon season is also the season of vegetative growing.

2.The dry season is affected by the cold air-mass from northern Asia. Temperatures and humidity drop. The monsoon rains completely stop. This is the time when the large-flowered cymbidium species stop growing, instead they are in a reproductive cycle. Literally, they are in the season of blooming.

The Mediterranean climate zones, cool summer /mild winter, such as the southwestern coast of the US, southern coast of Europe and South Africa, southern and southwestern Australia and New Zealand are considered perfect for most of the commercial large-flowered hybrids, which were derived from the Himalayan species. Because of their relatively temperate summers, the summer nighttime temperatures drop markedly. Plus, there is rarely a freezing period prolonged enough to damage plants or developing flowers. All traditional cymbidium hybrids feel at home under these conditions.

For areas of humid subtropical climates, with hot summer and cool-cold winter, such as most of the eastern coasts of various continents between latitude 25-40; e.g. southeastern & southern USA, southern & eastern China, most of Japan, the eastern coast of Australia, southeastern Brazil to northern Argentina, northern India and northern Vietnam, there is often a prolonged period of hot & humid summer weather, with high night temperatures. These conditions cause stress to conventional cymbidiums, and result in a lower energy storage in their pseudobulbs.

Such stress has a directly negative effect on the new pseudobulb growing during the summer. Those affected pseudobulbs may end up smaller than their genetic potential might suggest. As a result, those stunted pseudobulbs will yield poorer quality flowers and usually fewer spikes. In the worst scenario, those sub-standard pseudobulbs may not produce any blooms at all, even when they later experience autumn cooling. However those new growths growing in an environment of cool summer or at a higher elevation where night temperatures are lower, (lower than max. night temperature) will not suffer from such reduced quality.

Nowadays, growers can prevent these kinds of problem by growing varieties with a mixed background of tropical lowland species, namely Heat Tolerant Cymbidiums and Warmth Tolerant Cymbidiums. Both HTC and WTC do not require night temperatures as low as that of conventional or standard cymbidiums. In climates with a prolonged hot summer, the new growths of HTC and WTC will still initiate flower buds in their growths. Therefore, non-flowering or reduced-flowering growths can be prevented.

Stage II : Flower spike initiation (This stage requires max. night temperature lower than Stage I but higher than Stage III)

After the nearly-mature or fully-mature pseudobulbs with flower buds inside, have been exposed to lower night temperatures for a while, spikes will appear, emerging as cone-like nubs (similar to new growths but rounder) from the base of pseudobulbs or within the lowest leaf axils. These enlarging flower buds have been developing in the healthy new growths almost from their inception and will eventually become the inflorescences.

This is also a period when growers can manipulate spike maturation and alter how long it will take before they bloom. In a closed environment where temperature (the most important factor), light, water and fertilizers can be fully controlled, the timing of blooming is partly controllable.

The same varieties when grown in different conditions can be made to bloom over an extended period. The group that received the lower night temperature earlier will initiate flower spikes before other plants of the same clone. This can give an advantage over nurseries located in warmer places, with nurseries located at higher latitudes or at higher elevations experiencing earlier blooming.

Because both HTC and WTC have temperature trigger points of flower spike initiation higher than those of conventional/standard cymbidiums, they do not have to wait for the night temperatures to drop as low as the conventional/standard cymbidiums require. If HTC and WTC are grown alongside with conventional/standard cymbidiums, HTC will initiate their spikes first, followed by WTC and concluding with the conventional/standard cymbidiums. This means that nurseries located in warmer places or at lower elevations that grow HTC and WTC can have blooms no later than those that grow conventional/standard cymbidiums in cooler places or at higher elevations.

Stage III : Spike elongation and blooming (This stage is the most critical and requires max. night temperature lower than both Stage I and II)

When night temperature keeps dropping continuously and the days get milder or cooler, the flower spikes will elongate. Each flower bud will enlarge and finally bloom. Depending on the overall temperature profiles, it normally takes at least 30-60 days from when the new flower spikes become visible to the full bloom. In case that the autumn cooling is not stable, and especially if the night temperatures are not low enough, problems in spike development can become obvious. For example, the elongation may actually slow down, the lateral sepals become disfigured, colours lose their intensity, pollen does not reach maturity and may darken, or at worst, the whole spike can turn yellow and abort.

Normally, cymbidiums with larger flowers and taller upright spikes require lower temperature. They are more susceptible to bud drop due to heat stress than the varieties with arching or pendulous spikes and smaller flowers. Simply, the cut-flower varieties with the largest flowers and tallest spikes require cooler conditions during spike maturation than other varieties.

Cool-growing/conventional cymbidiums are vulnerable to an unstable cooler season, but this vulnerability is much less among the HTC and WTC varieties. HTC and WTC will help in reducing the problem of bud drop if the night chill is not stable and also in the higher temperatures plants frequently face during transportation and display in the city markets.

Conclusions & Extensions

Cymbidium nurseries that most quickly complete the three stages will have the blooms first and no problems with barren pseudobulbs.

At every stage, the cool-growing/conventional cymbidiums require lower temperatures than HTC and WTC do.

However, all cool-growing/conventional cymbidium hybrids do not require any temperature as low as 10 Celsius at any growth stage. In reality, many cymbidium nurseries, especially those that produce cut flowers, are located in climates where external winter temperature drop to lower than 10 Celsius at night throughout the whole of stage III. In addition, almost all of the cut-flower nurseries are located in a greenhouse or closed environment because this is necessary for providing warmth and the stable temperatures desirable during stage III.

Colombia and Ecuador are the two countries in equatorial zones that currently successfully grow cut-flower cymbidiums because they have plenty of suitable growing area at higher elevations. Cut-flower varieties are grown at 2600-2800 metres in Ecuador and above 1600 metres in Colombia. In these equatorial regions, the crops are not seasonal but rather year-round.