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How to grow the best Phalaenopses

Part 1: Temperature and light

This is the first in a series of articles about growing Phalaenopsis well, and I am grateful to the American Orchid Society magazine for the title of this article and for much of the information contained in this series.

We are told that we should try to replicate the growing conditions that a particular orchid experiences in its natural habitat to grow it well. Often the only information we can easily get is that the orchid likes warm or intermediate or cool conditions; or that it comes from tropical rain forests or the Andes mountains of S. America and so on. These are often so general a statement that we are no greatly the wiser. However with Phalaenopsis, they are now grown effectively as factory farming and there has been much research as to the exact conditions of temperature, light, feeding and so on needed to produce the best plants.

Phalaenopsis are native to the tropical and subtropical areas of Asia and the South Pacific Islands. In their natural habitat tropical conditions occur all year, with temperatures ranging from 28°C - 35°C by day and 20°C - to 24°C by night. They grow on tree branches and trunks shaded by the dense canopy of the forest, and so need warm and shaded conditions to grow best, especially when in the vegetative stage. This is when new leaves are growing. As the flower spike usually emerges from the third node (sometimes the fourth or second) below the uppermost mature leaf, and spikes developing on young plants with few or small leaves tend to be poor (e.g. few flowers) it is important to have a period when the plant is encouraged to grow new leaves. In commercial nurseries they do this by raising the temperature to at least 28°C by day. We may not find this easy to do in our houses but there are usually warmer places such as on windowsills behind net curtains. Remember, however, that Phalaenopsis leaves can be scorched by exposure to too bright sunlight. The size of the leaves can also be affected by the amount of light received. One of my Phalaenopsis that was in flower for a long time developed thin leaves due to being in too shady a position too shady a position - it was in a corner in the lounge with a north facing window nearby.

The flowering phase in a Phalaenopsis can be induced by a drop in temperature. After a hot spell in June and July this year the temperatures in August and September were much cooler. As a result between 80% and 90% of my Phalaenopses have developed new flower spikes, the exceptions being ones that have just finished flowering and those that have less than 3 mature leaves above the last flower spike. In commercial nurseries they might go for a 25°C by day, 20°C by night regime to induce flowering, but my greenhouse temperatures drop to a lower figure than that naturally and the change to cooler conditions gives the necessary kick start to the flowering phase. Do remember, though, that Phalaenopsis are tropical plants. If the temperature drops too much (10°C is definitely too cold) or fluctuates too rapidly the plant may be damaged or even killed by the cold. Unfortunately this damage doesn‘t always appear immediately. Some people whose Phalaenopsis plants were affected by the icy weather last January found that some of the plants died months later. The chill and temperature fluctuations can explain why Phalaenopsis bought at a show in the winter and adjacent months and brought home may lose some of the unopened buds. It is worth adding that experiments have shown that maximum spike production and flowering occurred when temperatures were kept between 20°C and 23°C for 10 to 12 weeks. Higher temperatures reduced the number of flowers and lower temperatures produced few or no flowers.

Jonathan Watson

Part 2 »»

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