October 2010 - Cool Culture

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Cool weather is here for most of us. Even South Florida is experiencing lower daytime temperatures and cool nights. The shortening day length and cooler nights initiate all sorts of changes in your orchids.

Many fall blooming cattleyas are getting ready to bloom and buds are swelling in their sheaths. C labiata, C bowringiana and the fall blooming form of C skinneri, and their hybrids typically have double sheaths. It seems that the big change in day to night temperatures can cause moisture to accumulate between the inner and outer sheaths causing buds to rot. Watch these orchids carefully and be sure there is lots of air movement around these orchids. If you observe any moisture accumulating, carefully open the outer sheath and allow air movement into the space between sheaths. That usually solves the problem.


Vandas are known as heat-loving orchids, but have always bloomed better for me in the fall and winter as long as temperatures do not get below 60 F and there is enough light. Colors are always brighter when nights are a little cooler. This is especially true for any Vanda or Ascocenda with Vanda coerulea in the parentage.

  Cool weather is here for most of us. Even South Florida is experiencing lower daytime temperatures and cool nights. The shortening day length and cooler nights initiate all sorts of changes in your orchids.
Many fall blooming cattleyas are getting ready to bloom and buds are swelling in their sheaths. C labiata, C bowringiana and the fall blooming form of C skinneri, and their hybrids typically have double sheaths. It seems that the big change in day to night temperatures can cause moisture to accumulate between the inner and outer sheaths causing buds to rot. Watch these orchids carefully and be sure they have lots of air movement. If you observe any moisture accumulating, carefully open the outer sheath and allow air movement into the space between sheaths. That usually solves the problem.


Vandas are known as heat-loving orchids, but have always bloomed better for me in the fall and winter as long as temperatures do not get below 60 F and there is enough light. Colors are always brighter when nights are a little cooler. This is especially true for any Vanda or Ascocenda with Vanda coerulea in the parentage.


Phalaenopsis require a significant day to night temperature change to initiate spikes. It usually takes a couple of weeks of these conditions to get all of the phals in a greenhouse to put their energy into growing spikes instead of leaves. Phals will be fine on a porch or in a greenhouse even after nights are in the upper 50s F as long as the day temperature rises above 80 F. Once daytime high temperatures are below 78-80 F, phals need to be kept no lower than 60 F at night.
Paphs and phrags really seem to love the cool nights too. Mature growths, especially in the multifloral paphs will prepare to flower. Usually development of new growths is the first sign that a flower spike will soon emerge.


Essentially, I stop fertilizing cattleyas (except seedlings) starting in October and reduce watering frequency, but not watering intensity. Less light and heat each day means that orchids dry out less rapidly. Pay careful attention to periods of clouds and rain, which can also lead to less need for water.

 
Some books recommend switching to high phosphate fertilizers for phals, paphs, vandas, and other orchids that do not have a rest period before flowering. For years I did this, but finally decided that maintaining a high nitrogen fertilizer gave me better flowers and more of them. Because watering is reduced and fertilizer is provided with each watering, there is a reduction in fertilizer, but that is the only change.


Cymbidiums are not widely grown in the Deep South, but can do well here. If you have some of these genera, now is the time to move them into increased sunlight. Best results occur when Cymbidiums are kept under heavy shade during the intense summer heat. Now, give them a good shot of fertilizer and slowly move them into the sunlight. Unless you have one of the tropical forms, they can take temperatures near freezing and seem to bloom best when they have a light frost on their leaves at sunrise. Once you see bloom spikes emerging, protect them from extreme cold until they flower.