AUSTRALIAN NATIVE ORCHIDS IN WINTER by Jim Doney
What is different during winter that will affect the growth of Australian native orchids?
- Light diminishes in strength
- Plants dry out more slowly after watering
- Plants grow more slowly
What do we need to do to compensate for these changes?
What signs can we expect to detect in happy plants?
- Increase light levels by removing any shading
- Extend the interval between watering
- Reduce the application of fertilisers
- Good white roots
- Nice solid leafy growths
- Glossy leaves
If you are happy with the growth of your plants, continue with your cultural program - don't be persuaded to adopt the procedures of other growers. On the other hand, if you're dissatisfied with the progress of your plants, try some alternatives. Should you decide to try some new ideas, carry them out on a small scale to see if they work before applying them to your whole collection. Observe your plants closely and try to identify any problems.
Conditions are still good (in April) for re-potting. Make sure that you use a pot of appropriate dimensions for the size of the root mass - DO NOT over-pot. Depending on your location and your watering habits, use a potting mix that drains adequately but doesn't dry out too rapidly. If your plants have rotten roots, determine the cause and take remedial action. Remove all rotten roots and any growths without leaves or roots to promote new growth.
Different plants need different positions. For example, I find that Dendrobium Tweed and D. Red River grow better when their pots are hung low down than when hung high. On the other hand, Sarcochilus ceciliae and S. hartmannii need higher light levels than S. fitzgeraldii and most other sarcochilus species and hybrids. In my experience, some orchids, such as Sarcochilus australis, Rhinerrhiza divitiflora and Peristerchilus Olive Grace, need to be kept drier than others.
Humidity, aeration, air movement and good light are vital for good culture. What can we do to ensure that these factors are satisfactory?
- Humidity. Ensure that you have a layer of water-retentive medium, such as gravel or scoria, on the floor below your benches to hold moisture and provide humid air around your plants.
- Aeration. Ensure that the composition of your potting mix allows for pockets of air between the roots and the particles of mix.
- Light. Make sure that no trees or buildings block the light falling upon your plants, especially from the north and east.
- Air movement, either natural or generated by electric fans, is vital to maintain healthy plants. Improvements in this area will help to reduce the incidence of scale and spider mite.
- Watering in the morning on warm or windy days ensures that the foliage dries by nightfall, thus helping to minimise fungal infections.
- Pests. Snails, slugs and grubs are the main pests during winter. Use carbaryl-based sprays for grubs and caterpillars, and Baysol® or other pellets* for slugs and snails.
* WARNING : Most snail baits are poisonous to pets.