Program notes and video: Paphiopedilum cultural tips from Sam Tsui, Orchid Inn

[Program notes for the October meeting featuring Sam Tsui were provided by OSGKC member, Susie Hanna.]


  • Artificial Light
  • High-Pressure Sodium Light: 400-1000 Foot Candles (FC)
  • T5 Fluorescent bulbs:  500 fc
  • Natural Light:
  • 500-1500 fc
  • Window: East/West Exposure


  • Winter: 30-40% shade cloth
  • Summer: 60-80% shade cloth


  • Second most important factor for growing.  Phrags particularly demand water with low mineral content
  • 300 ppm total dissolved solids ok for most paphs, except for besseae and a few other species.
  • RO Water – very pure, 5-10 ppm.  He uses RO water mixed 50 percent with well water to get about 100 ppm for his orchids.


  • Spring and Summer (Growth phase): 30-10-10 formula
  • Fall and Winter: 20-20-20 
  • He likes the weekly weakly method.  Paphs don’t need strong fertilizer.  Use ¼ tsp or less.
  • Leach or flush with plain water once a month.
  • He waters his plant thoroughly first, then applies fertilizer as a mist which provides foliar feeding as well as root feeding.  Watering first avoids root burn.


  • Ideal: 60 low and 85 high
  • Low Limit: 50
  • High Limit: 95
  • Prefer 10-15 degree temperature differential between day and night.  This helps initiate bloom spike.

Air Movement:  Always.  Very Important

Humidity: 50-70%

Media and Potting:

A fir bark mix.  The best bark now is the New Zealand type.  Some of his customers report that the NZ bark is viable for up to four years without repotting.  Paphs don’t like to be repotted.  Many of the old roots die in the process and it takes the plants 6 months to recover.  If you need to repot and the media is still good, just carefully transfer the plant with the media to a slightly larger pot.  It’s very important not to overpot.  They like to have their roots packed in the pot.

His potting mix:

  • 4 parts fine or medium bark.  Use medium bark for 4-inch or larger pots.
  • ½ part sponge rock (large perlite)
  • ½ part charcoal, #3 or #4 size
  • ¼ cup dolomite per 10 gallons of this mix.

You can also top dress the plants occasionally with dolomite or oyster shells.  This provides the calcium that is critical for paphs since many of them grow in areas of limestone.  Use about 1 tsp for top dressing.


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