Light: 3,000-4,000 foot candles. I grow them basically in the same level of light I would grow one of my Cattleyas. Check leaf temperatures if in doubt to whether your light situation is too bright. If the leaves feel hot, move them away from the light source slightly. Phrag leaves can sunburn like all orchids, so move them into different light conditions gradually. Many successful Phrag growers grow under light fixtures in the home.
If you are growing in the home and choose to not use light fixtures a bright and sunny southern exposure window that receives indirect light for five or more hours will be satisfactory. You may need to supplement their light by moving your Phrags outdoors during the warmer months when nighttime temperatures remain above 55 degrees. Make sure your outdoor growing area is shaded and your plants receive gentle morning sun at the maximum.
Temperature: They seem totally happy with a temperature range from 55 to 90 degrees. When temperatures drop lower be more cautious about letting water stand in the leaf axis. Standing water at lower temperatures can lead to bacterial rot problems. A good practice to follow is early morning watering and making sure leaf surfaces are dry by nightfall. Phrag besseae is from a higher elevation than most Phragmipediums and thus would stand to reason that it would enjoy and benefit from cooler day and night time temperatures.
Air Movement: All orchids appreciate good air movement and Phrags seem to do best when a breeze is blowing strong enough to gently move the leaves. Water will dry off leaves much faster when an air source is provided.
Flower Color with regards to temperatures: Flower color is greatly intensified on Phragmipedium flowers if you can keep temperatures cooler. You will have more evenly distributed color on your flowers and the colors will be richer and darker shades.
Water Quality: All Phragmipediums benefit from water that is lower than 300 ppm of dissolved solids. Your water source can be tested by a testing lab and the results can be sent to you. You will then know the make-up of your water. If you find your normal water source to be high in dissolved solids, then you would be better off with another water source such as collected rainwater. Distilled water and reverse osmosis water are fine choices for a water source, but remember that when adding fertilizer to these sources, the ph level of the water will go down drastically and will need adjusted back closer to 6.0-6.8. Ph adjusters are widely available. I recommend the addition of fertilizers that contain macro and micro-nutrients if rainwater is your watering source and macro and micro nutrient fertilizers must be used whenever distilled or reverse osmosis water is your water source.
Watering: Water Phrags year round and keep them moist, not soaking wet. Water and then let them dry somewhat before watering again. If Phrags are allowed to dry too long between waterings you may experience leaf tip die back.
Fertilizer: I fertilize my Phrags with very dilute fertilizer every 4th-6th watering, I use a water soluble 10-10-10 or 20-20-20 at 1/4 teaspoon per gallon. If growing Phrags in a bark mixture, you will want to use 30-10-10 at the same dilute quantities. Some people top dress twice a year (Spring and Fall) with a 50/50 mixture of dried bone and blood meal. A quantity of one teaspoon dressing on a 6-inch pot. After placing this top dressing, water thoroughly. I do not recommend this for in the home growers, for many will find the smell offensive. I do not have much experience using the bone and blood meal top dressing in our greenhouse, so at this time I can't comment on its benefits or detriments.
Repotting: Repot Phrags every six to nine months. They benefit from new fresh mix that has no traces of fertilizer buildup in the mix. As the mix gets older, fertilizer (salts) can gradually increase in the mix and actually start to poison your plants. Since Phrags enjoy good water quality, changing the mix every six to nine months will avoid any fertilizer buildup remaining in your pot. Also, a mix that is subjected to high moisture will break down more quickly than a mix used for orchids that are allowed to dry between waterings. Since Phrags like year round moisture, the frequent repotting schedule will make sure your plant is not sitting in a broken down mix and possibly losing valuable roots.
Seagrove Orchids, Seagrove, NC 27341-9019 336-879-6677