Culture/Growing - The Cooktown Orchid
(Dendrobium bigibbum)

(The Cedarvale Way)

These notes are intended to cover growing in shade-houses, etc, as well as landscape plants. These notes are also available to download.

LOCATION OR GROWING HOUSE I grow these plants in a purpose-built tunnelhouse house covered with opaque solarweave.  This enables me to keep the plants dry and warmer in the winter and, by closing the doors and vents in mid-afternoon,  I believe that the plants will tolerate the cold and the wet but not a combined cold and wet.  I have found plants in a shade-cloth covered house to deteriorate in cold, wet winters.

LIGHT I grow the plant in bright light, given that opaque solarweave transmits 50% light.  The inside roof has an additional 30% shadecloth to reduce the heat more than the light. (I am not sure that the light levels are changed given the manner in which the solarweave refracts the light).

VENTILATION  I believe that ventilation is the most important aspect of good orchid culture in general. "Orchids love to be wet and love to be dry" and good ventilation will dry them rapidly, dramatically reducing fungal and bacterial rot occurrences, reducing the need for chemical sprays and thus saving you money. I am lucky enough to have very good ventilation without the standard small block problems of nearby houses, sheds, fences, trees, etc.

WATERING is an individual action and is dependent upon the individual conditions that the plant is grown in.  Such aspects as ventilation (how fast do the plants dry out), potting medium eg bark or sphagnum moss, is the mix new or old? The best general advice is that if the mix is open, drains and dries well then you can water freely in the summer (September to March). In winter (April to August) cut back on the water to once a week or fortnight (depending on whether there is a westerly wind or not).  More native orchids are killed by over-watering than any other action.  Resist the urge to water and go and have a drink yourself.  Slight shriveling of the canes of the plants during winter is not a problem; summer watering will fatten them up again. Remember where they grow naturally they have monsoon downpours in the summer and can have no rain at all for 2 - 3 months in the winter.  When I water in the winter I do so in the morning on a bright sunny day, breezy if possible, to ensure that the plants are relatively dry before nightfall.  In summer I water from 4.00pm onwards to avoid water laying in new growths during the heat of the day, which I have found encourages bacterial rot of the new growths.  I have an automatic misting system located under the benches which waters the floor each day to try to maintain humidity all year round.  I believe this helps prevent leaf-drop.

RE-POTTING - Only repot when the orchid reaches the sides of the pot. However our potting mix will only last two years and the orchid should then be repotted with fresh medium.  At Cedarvale we mainly use 70% bark and either 30% jumbo perlite, 15mm Maidenwell Diatomite or 25mm Maindenwell Diatomite (depending on pot size) as a potting medium, 10mm grade up to 100mm pots, 15mm for all else.

FERTILISING   Try to fertilise weekly and weakly (1 gram/litre) in the growing season, September to December, with a low level nitrogen fertiliser, NPK 14:5:22, and change to higher level phosphorous and potassium fertiliser, NPK 7:11:27, in flowering season, January till the flowers drop.  The plants make new growths, flower from those growths and set seedpods between September to April so frequent feeding is almost mandatory for best results.


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